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    My Journey through the Astronomical Year

    Think of this as a "companion text" to this, the main web site. Not required reading, butI hope you'll find it interesting and helpful.

Look East in February 2014: Two dogs – plus Jupiter – rising in a star-spangled spectacular – the Winter Hexagon

We have two “dog stars” on the southeastern horizon early on February evenings  – Sirius and Procyon – and  both are part of what is certainly the brightest, star-spangled  section of our northern night sky – the Winter Hexagon.  Adding to this annual dazzle in 2014 – and brighter than any star – is the “wandering star” (i.e., planet) Jupiter, smack in the middle of the Gemini twins -about halfway between their heads and feet.

Here’s how the Winter Hexagon looked to the camera of Jimmy Westlake who took this gorgeous shot as it loomed over Stagecoach, Colorado, USA.  You may not see the faint band of the Milky Way shown here if you live in a light polluted region, but you certainly should be able to pick out the bright stars that outline the Hexagon, as well as the Pleiades star cluster visible near the top and just right of center.

Click on image for much larger view! (Copyright © 2007-2011 JRWjr Astrophotography. All rights reserved.)

Look carefully at that photo, then compare it with this star chart, which is what we see from mid-northern latitudes as we look southeast early on a February evening.

Click image for much larger version. To get the full beauty of this section of sky find an area with a clear horizon to the southeast and go out on a February evening a couple of hours after sunset. The chart shows what you'll see. The link below provides a small black-on-white version you can print and take into the field. (Prepared from a Stellarium screen shot.)

Click image for much larger version. To get the full beauty of this section of sky find an area with a clear horizon to the southeast and go out on a February evening a couple of hours after sunset. The chart shows what you’ll see. The link below provides a small black-on-white version you can print and take into the field. (Prepared from a Stellarium screen shot.)

For a printer-friendly version of this chart, click here.

People in the north tend to think that the stars are brighter in winter because the air is so cool and crisp. That certainly could be a factor. But the simple fact is our winter sky is dominated by a whole lot of very bright stars. In fact, visible from earth are 22 stars of first magnitude. Sixteen  of these are visible from the Northern Hemisphere, and half of these are visible in the area of the Winter Hexagon on a February evening. That means nearly all these bright stars are jammed into a space taking up less than one-quarter of the February night sky – which is  just one-eighth of the total night sky we can see through the year! In other words, if bright stars like these were scattered throughout the night sky evenly there would be 64 first magnitude stars instead of just 22. Add to that the seven bright stars of the Big Dipper being dragged up the northeastern sky by the Great Bear on a February evening, and it is no wonder that in the dead of a northern winter our skies offer a lively, colorful, star-spangled spectacular.

The Hexagon alone contains seven of the first magnitude stars in our sky and an eighth that is the brightest second magnitude star we see. This one – Castor – just misses being first magnitude by a hair.  And nearby is Adhara, a star that sits right on the border between second and first magnitude; plus Regulus, another first magnitude star, is rising low in the east. Whew! That’s a lot. Let’s review.  Going  counterclockwise and starting at the bottom, the Hexagon’s corners are marked by:

  • Sirius, the brightest, and at about eight light years one of the closest, stars in our sky – except the Sun, of course.
  • Rigel, the blue giant that marks one of Orion’s feet.
  • Aldebaran, the brilliant orange star that is the eye of Taurus the Bull and dominates the nearest open star cluster, the Hyades.
  • Capella, now high overhead, is really a complex of four stars that we see as one.
  • Castor and Pollux, the twins, one of which (Pollux) is first magnitude, while Castor is the brightest second magnitude star we see.
  • Procyon, the “Little Dog” star, which is dim only in comparison to Sirius, the “Big Dog.”

And . . .

  • Inside the Hexagon is another first magnitude star, Betelgeuse, the red giant that marks Orion’s shoulder, not to mention the three bright stars of Orion’s Belt – all second magnitude.
  • Regulus, the “Little King,” is a first magnitude star that is rising in the east and bringing us the familiar sickle of bright stars that mark the head of the lion. We’ll study it closely next month.
  • Adhara is the western-most star of the distinctive small triangle of stars beneath Sirius. At magnitude 1.5 I call it a first magnitude star, but others consider this second magnitude. So depending on how you count Adhara there are either 21 or 22 first magnitude stars.

Before leaving the Winter Hexagon, I must stress that  this is not simply a northern hemisphere show – if you live  in Sydney, Australia, you could just rename this the “Summer Hexagon.” I see these stars in the southeast – my friends in Sydney see them in the northeast of their sky – and, of course, since they’re “standing on their heads,” they see them a bit differently – something like this!

The “Winter Hexagon” becomes the “Summer Hexagon” in the Southern Hemisphere, but contains all the same bright stars. (Chart prepared from Starry Nights Pro screen shot.)

February Guidepost Stars

Of the stars mentioned so far, the two dog stars, Sirius and Procyon, plus the fence sitter, Adhara, are the guidepost stars to learn this month. They are the ones you can spot near the southeastern horizon, coming into view about 45 minutes to an hour after sunset. (We’ll have more to say about Regulus next month, and the other stars mentioned we’ve met in previous months.) To see the February guidepost stars – and the asterism of the Virgins –  look low in the southeast about 45 minutes to an hour after sunset.  Here’s what you should see.

Click image for larger version. This chart shows the three guidepost stars for February as they appear about an hour after sunset in the southeast. Sirius is the brightest star we see and Procyon is not far behind, but Adhara is not much brighter than its companions, which form a distinctive, small triangle the ancient Arabs knew simply as “the Virgins.” (Prepared from Starry Nights Pro screen shot.)

For a printer-friendly version of this chart, click here.

Procyon, the seventh brightest star we see, is first up in our sky, and thus the highest, of these three. To the southeast and a tad lower is brilliant Sirius, brightest star in our sky, and next to the North Star, Polaris, probably the best known star in the world. Adhara is the brightest star in the “Virgins,” a simple,  distinctive  triangle asterism. But, of course, Sirius is dominant – far brighter than any other star we see in our night sky. I always think of Sirius as the eye of the great dog and as he sits, the triangle seems to be his rear haunches. From our perspective Adhara may be just another bright star, but of these three it is really the brightest by far – it’s just much farther away than the other two.  If we compared them side by side we would find that Procyon shines with the light of seven Suns, Sirius 23, and Adhara has a luminosity to the eye of 3,700 Suns! Now that’s bright.  And in another way, Adhara reveals our human bias, for if we had ultraviolet vision Adhara would be the brightest star in our sky, not Sirius. But again – that’s not the way we see it. From our perspective, Sirius and Procyon are very bright because they are very close to Earth. Sirius, at a little more than eight light years is the closest star that we in the mid-northern latitudes see in our night sky. Procyon, at about 11 light years, is fourteenth on the list of nearest stars.  Most of the stars that are nearer than Procyon are also much fainter – in fact, too faint to see with the naked eye. If we count just those stars bright enough to see with the naked eye, Procyon is the sixth closest and Sirius is the second closest.  (The closest star, Alpha Centauri, is visible only to those in, or near, the Southern Hemisphere.) But Adhara? Adhara is 405  light years away – about the same distance as the North Star, Polaris. Sirius will frequently seem to be changing colors, but that’s just the effect of our atmosphere. Just as our atmosphere makes our Sun look red when it is rising or setting, it makes any bright star near the horizon appear to dance and change colors rapidly.

The Big Dog as Johannes Bayer depicted him in 1603. (Image courtesy of Linda Hall library of Science, Engineering and Technology.)
The Little Dog as shown in the 1603 Uranometria chart. (Image courtesy of Linda Hall library of Science, Engineering and Technology.)

Sirius is known as a “dog star” because it is the brightest star of the classic constellation, Canis Major – the Big Dog. Procyon is the brightest star in the constellation Canis Minor, the Little Dog. When you look at these constellations as depicted in early star charts, it’s hard to see how connecting the dots makes the stars take the forms the constellation’s name implies, but the images are still useful memory joggers.

Modern science, though, gives us even more reason to remember these two stars, or rather the faint companion stars that orbit them. These are designated Procyon B and Sirius B and they defy our ability to even imagine because there’s just nothing in our down-to-earth experiences that compare with these tiny stars.  One of these “pups”  – the one belonging to Procyon – is impossible to see with a backyard telescope and the other an extreme challenge.  The reason is they are quite dim and being very close to the bright stars, get lost in the glare.

But the mystery of these two fainter stars is that they are both white, indicating they are among the hottest of stars. So how could something be that hot, that close to us, and yet so dim? And the answer is more mind-boggling than the question – they are both white dwarfs, and white dwarfs are a class of stars far denser than anything we encounter on Earth. Now I always find talk of the density of stars counter-intuitive because it gets drilled into our heads that stars are gas and the gas we encounter in our daily lives is anything but dense!  In fact, it’s quite – well – gaseous!  To appreciate this, let’s take a close look at our own Sun.

Click image for larger view.Sirius – with Sirius B at lower left.  Credit: NASA, H.E. Bond and E. Nelan (Space Telescope Science Institute, Baltimore, Md.); M. Barstow and M. Burleigh (University of Leicester, U.K.); and J.B. Holberg (University of Arizona)

The Sun is a ball of gas which reaches densities that near the center are sixteen times that of lead!  That alone should stretch your mind. But now imagine the white dwarf. The stuff that makes up a white dwarf is about one million times denser than the stuff in the Sun.

Jim Kaler writes that if you had a billiard ball made up of the stuff of one of these white dwarfs it would weigh about 70 tons – roughly the weight of an M1 Abrams tank. (Think of what that would do to your pool table, not to mention your foot if it fell on it!)

We know this because we can calculate the mass of the stars by their orbit around their bigger, brighter companions. The result is, we end up with a mass roughly that of the Sun but a size roughly that of the Earth. You can fit one million Earths – and therefore one million white dwarfs – inside the Sun. (See why a white dwarf is one million times as dense as the Sun?)

How do you take all that mass and squeeze it down to such a small size? The physics of how that’s done goes way beyond me, but if you want to put a name to it, a white dwarf consists of “degenerate matter.” Unlike other stars, white dwarfs no longer burn with nuclear fires. In fact, they are no longer burning at all. They are the dying embers of stars – and in the case of the “pups,” the embers are being seen while still white hot. But they will eventually cool.

The name white dwarfs is given to this class of stars, but in truth not all white dwarfs are white – some can even be red. To make sense of this contradiction of terms, just think about an ordinary dying ember and how its color will change as it cools. So it is with these dying stars. Unable to generate any heat, what they radiate they lose.

This is also the ultimate fate scientists expect for our Sun.  As it eventually exhausts its nuclear energy, it will turn into a bloated red giant like Betelgeuse in Orion.  Later still it will blow off its outer shell of gases, turning into a planetary nebula, such as the Ring Nebula (M57) in Lyra.  And at the core of that nebula will be the dying ember we know as a white dwarf.

I’ve never seen the white dwarf that revolves around Sirius, but perhaps this season I will. Orbits are not circles, but ellipses. This means that sometimes there’s more distance between Sirius and its “pup” than at other times – and we happen to be in a period of several years when that distance will be growing, and so it will become easier to see the pup in a good, backyard telescope. (Sirius B completes an orbit around Sirius A in 50.2 years. Procyon B, while visible to professionals, is just simply too difficult a target for most backyard telescopes.) I also plan to take a close look at Adhara with a telescope, for it has a 7.5 magnitude companion just 7 arcseconds away. This should be a challenge – because of the difference in brightness of the two –  but not nearly the challenge that seeing the companion of Sirius is. For those with binoculars and small telescopes, some of the most fascinating objects are in this general area of sky, near, or inside the Winter Hexagon, including the Pleiades, the great Orion Nebula, and the spectacular telescopic open clusters in Gemini and Auriga, M35, M36, M37, and M38. All that star light certainly can make for bright nights during the dark  of a northern winter.

Vital Stats for the Guidepost Stars

For Procyon:

  • Brilliance: Magnitude 0.38, the 7th brightest star in our sky. Shines with the luminosity of about 7 Suns.
  • Distance: 11.4 light years
  • Spectral Type: F
  • Position: 07h:39m:18s, +5°:13′:29″
  • Procyon B is magnitude 10.7 and orbits Procyon in 40.8 years.  It can be as close as 9 AU to Procyon (1 AU is the distance between the Earth and Sun), or as far as  21 AU.

For Sirius:

  • Brilliance: Magnitude -1.5,  the brightest star in our sky.  Shines with the luminosity of about 23 Suns.
  • Distance: 8.6 light years
  • Spectral Type: A
  • Position: 06h:45m:09s, -16°:42′:58″
  • Sirius B is magnitude 8.3 and orbits Sirius in 50.2 years. It can be as close as 8.1 AU to Sirius, or as far as 31.5 AU. (It will reach this greatest separation in 2019.)

For Adhara:

  • Brilliance: Magnitude 1.5, it has a luminosity to the eye of 3500 times that of the Sun! (In other words, much brighter, really, than Procyon or Sirius.)
  • Distance: 405 light years
  • Spectral Type: B2
  • Position: 06h:59m, -28°:59′:18″

Look North in February 2014 – Watch the Great Bear Come out of his Cave!

When you look to the northeast early on a February evening do you see this:

or maybe this:

Used by permission from the Linda Hall Library of Science, Engineering & Technology.

or perhaps this?

It all depends, of course, on your imagination, but for me I see something like the last image. Even that doesn’t quite capture what my imagination wants to do with these stars. What I see is a huge and rather grumpy bear, emerging from his cave a bit early after hibernating through a few rough months, and now he’s stretching – and clawing – his way up my sky, and he is magnificent!

But I admit, for years it wasn’t that way. I saw instead what I suspect many people see – the Big Dipper rising. And I knew, sort of vaguely, that this asterism – one of the most familiar in the world – was a major portion of the constellation of the Great Bear, Ursa Major.  But really, large as the Dipper is, it’s just the hind quarters of the Big Bear, which is really large, and when I finally took the time to trace out his head and ears and front and rear paws, he quickly became one of my favorite constellations – one of the rare ones like Orion and Scorpius that really look like what you expect from their names.  And funny – I can’t explain why –  but I seldom see it as a bear except at this time of year when it is rising. Then it seems to dominate my northern sky and my imagination.

Oh – did I say it looks like a bear? No – I should have said it looks like a bear no one has seen except in the sky – a bear with a long tail! I don’t know why that is. I assume it is because of the second depiction, which is how Johann Bayer pictured the Great Bear in his “Uranometria,” a breakthrough star atlas published in 1603.  Bayer was a lawyer, not a hunter. Maybe he had never seen a bear?

The first depiction, a Stellarium screenshot, is the best one to use as a guide for finding the correct stars. Besides the Dipper stars, there are a dozen more that trace out his main features, and all of these are either third magnitude, or on the brighter side of fourth magnitude – that is between 3.5 and 4, so they should be visible from most locations – assuming, of course, you are in mid-northern latitudes.  The chart that follows gives a view of the Bear in context with the rest of the northern sky in February.

About one hour after sunset, look north and you should see a sky similar to the one shown in our chart below. The height of Polaris, the North Star, will be the same as your latitude. Polaris stays put.  Everything else appears to rotate about it, so our view of all else changes in the course of the evening – and from night to night. It’s a good idea to check the north sky every time you observe to get a sense of how things are changing and to orient yourself.  Notice that the “W” now looks more like an “M” as it starts to roll on down into the northwest.

Click image for larger view. (Chart derived from Starry Nights Pro screen shot.)
Click here to download a printer-friendly image of the above chart.

Events February 2013 – now that’s close but Mercury will be more fun!

Here’s a prediction: The news media will focus about mid-month on a tiny object you can’t see – and ignore a dazzling appearance by zippy Mercury and its meeting with Mars that you can see!

The tiny object you can’t see is asteroid 2012 DA 14  and it will get all the attention because it will be passing very, very close to Earth – well, very close in space terms – something like 18,000 miles in real terms.  No, don’t get nervous – it won’t hit us. (Of course, I’ve read three different predictions of how close it will come, but what’s a small error among friends 😉 Anyway, to put that in perspective, that’s about 60 times farther from us than the International Space Station, but closer to us than our geosynchronous satellites orbit and roughly one-twelfth the distance to the Moon.

NASA chart - click for larger image

NASA chart – click for larger image

Yep, that’s close. But when it happens, this asteroid – which is roughly about half the size of a football field – will be magnitude 8 – barely visible in good binoculars – and at that, visible only to observers in Europe and Asia who look in just the right place at just the right time.  (To find out where to go – and what to input – in order to learn where and when to see it, read this Sky and Telescope post.)

Now Mercury is a sight worth seeing – and not half as challenging

OK – a much, much easier target, though whimsical and quick in its own right – is Mercury, which does a little dance with Mars early this month before climbing into easier view a week later – then doing a heavenly Cheshire Cat act andvanishing almost as quickly as it appeared, which is why we frequently put the word “fleeting” in front of the name “Mercury.” And finding Mercury low in the southwest will be a great warm-up exercise for Comet PanSTARRS – scout out a good observing spot with unobscured western horizon to see Mercury and you have your ring-side seat for Comet PanSTARRS in March!

Start on February 7th and/or 8th

Mercury and Mars on the evening of February 7, 2013 about half an hour after sunset.

Mercury and Mars on the evening of February 7, 2013, about half an hour after sunset.

Here’s the drill:

  • Find an area with an unobstructed western horizon.
  • Go out just before sunset and note where on the horizon the Sun sets – it will be about halfway between west and southwest.
  • Wait half an hour and look for Mercury to emerge in the twilight less than a fist – about seven degrees – above the horizon and just a tad south of where the Sun set.
  • Use binoculars. Though you probably will be able to see Mercury with your naked eye – it is magnitude minus one –  Mars at magnitude one (more than six times fainter) will be much more difficult. But if you can find Mercury in your binoculars, you should see Mars as well. One quibble – they are very close to each other, and you may need to mount your binoculars on a tripod to split them – or even use a small telescope. Exactly how close depends on exactly where you are viewing from – they will be a bit closer for viewers on the West Coast than for those on the East Cast of the US.

As the twilight deepens they will be easier to see – but at the same time they will be getting closer to the horizon and thus more difficult to see because you are looking through more disturbed air at that point.  This is exactly the kind of race you are likely to have next month with Comet PanSTARRS, which will be near the western horizon after sunset and will get easier to see as twilight deepens – and yet, more difficult to see as it moves lower. With such objects there is always a time – totally unpredictable because it depends on local conditions – when you have the best view.

If the weather doesn’t cooperate, try the same drill on either of the next two nights. Mercury will be zipping by Mars. They actually are so close on February 8 it will take a small telescope to “split” them – they will be like a double star.  On February 9 Mars will be below Mercury and should be easy to see again in binoculars.

Best View of Mercury Alone

From the 11th – when Mercury is quite near the Moon – to the 20th, Mercury will be quite easy to see.

On the 11th it’s about five degrees below a very thin crescent Moon – should be able to just squeeze the two in a typical, low-power binocular field of view.

Each night Mercury will continue to be higher at the same time – about 30 minutes after sunset – BUT it is toying with us because as it gets higher it also gets dimmer! On the 11th it is still about minus 1 in brightness.  By the time it reaches its peak in height – around the 16th-to-18th – it has dropped to near magnitude zero. It continues to be quite high up through the 26th, but by that time it has dropped to magnitude 2 – a real challenge to pick out in the twilight.

Bottom line – try to catch it near Mars – that’s really fun. And if you miss that – try to catch it between then and the 19th or 20th. Oh – and if you do have a small telescope, it will make an interesting sight during these twilight hours. Talk about the Cheshire Cat, it will be smiling at us – really! Around the 12th it will look a bit like a quarter moon – half  lit. Twelve days later it will be just a thin crescent – which is why, of course, it is getting dimmer! So the smile gets bigger as the celestial cat vanishes. Oh my!

What else is there?

Well you can’t ignore Jupiter, high in the southeast evening sky with its four major moons continuing to dance about it. It resumes its eastward movement against the background stars, very slowly moving closer to Aldebaran.

And Saturn is putting in a solid appearance in the morning sky. At mid-month it is due south and about 35 degrees above the horizon two hours before sunrise.

And on the moonless evenings early – or late – in the month, don’t miss the chance to see the Zodaical Light.  Best time to look is 80 minutes after sunset. It will be a faint, conical glow rising up from the western horizon – about the brightness of the Milky Way.  You do need skies free of light pollution to pick it out. For more on the Zodaical light, see this post from last year – scroll down to the heading “Basking in the Zodaical Light.”.

Look East in February 2013: Two dogs – plus Jupiter – rising in a star-spangled spectacular – the Winter Hexagon

We have two “dog stars” on the southeastern horizon early on February evenings  – Sirius and Procyon – and  both are part of what is certainly the brightest, star-spangled  section of our northern night sky – the Winter Hexagon.  Adding to this annual dazzle in 2013 – and brighter than any star – is the “wandering star (ie.planet) Jupiter, just above Aldebaran.  (Jupiter doesn’t show in our pictures and charts, but you can’t miss it when you go out to look at this section of the sky this year. )

Here’s how the Winter Hexagon looked to the camera of Jimmy Westlake who took this gorgeous shot as it loomed over Stagecoach, Colorado, USA.  You may not see the faint band of the Milky Way shown here if you live in a light polluted region, but you certainly should be able to pick out the bright stars that outline the Hexagon, as well as the Pleiades star cluster visible near the top and just right of center.

Click on image for much larger view! (Copyright © 2007-2011 JRWjr Astrophotography. All rights reserved.)

Look carefully at that photo, then compare it with this star chart which is what we see from mid-northern latitudes as as we look southeast early on a February evening. (And as noted, in 2013 there will be a “star” brighter than all the others in the chart – the planet Jupiter.)

Click image for much larger version. To get the full beauty of this section of sky find an area with a clear horizon to the southeast and go out on a February evening a couple of hours after sunset. The chart shows what you’ll see. The link below provides a small black-on-white version you can print and take into the field. (Prepared from a Stellarium screen shot.)

For a printer-friendly version of this chart, click here.

People in the north tend to think that the stars are brighter in winter because the air is so cool and crisp. That certainly could be a factor. But the simple fact is our winter sky is dominated by a whole lot of very bright stars. In fact, visible from earth are 22 stars of first magnitude. Sixteen  of these are visible from the northern hemisphere and half of these are visible in the area of the Winter Hexagon on a February evening. That means nearly all these bright stars are jammed into a space taking up less than one-quarter of the February night sky – which is  just one-eighth of the total night sky we can see through the year! In other words, if bright stars like these were scattered throughout the night sky evenly there would be 64 first magnitude stars instead of just 22. Add to that the seven bright stars of the Big Dipper being dragged up the northeastern sky by the Great Bear on a February evening, and it is no wonder that in the dead of a northern winter our skies offer a lively, colorful, star-spangled spectacular.

The Hexagon alone contains seven of the first magnitude stars in our sky and an eighth that is the brightest second magnitude stars we see. This one – Castor – just misses being first magnitude by a hair.  And nearby is Adhara, a star that sits right on the border between second and first magnitude; plus Regulus, another first magnitude star, is rising low in the east. Whew! That’s a lot. Let’s review.  Going  counterclockwise and starting at the bottom, the Hexagon’s corners are marked by:

  • Sirius, the brightest, and at about eight light years one of the closest, stars in our sky – except the Sun, of course.
  • Rigel, the blue giant that marks one of Orion’s feet.
  • Aldebaran, the brilliant orange star that is the eye of Taurus the Bull and dominates the nearest open star cluster, the Hyades.
  • Capella, now high overhead, is really a complex of four stars that we see as one.
  • Castor and Pollux, the twins, one of which (Pollux) is first magnitude, while Castor is the brightest second magnitude star we see.
  • Procyon, the “Little Dog” star, which is dim only in comparison to Sirius, the “Big Dog.”

And . . .

  • Inside the Hexagon is another first magnitude star, Betelgeuse, the red giant that marks Orion’s shoulder, not to mention the three bright stars of Orion’s Belt – all second magnitude.
  • Regulus, the “Little King,” is a first magnitude star that is rising in the east and bringing us the familiar sickle of bright stars that mark the head of the lion. We’ll study it closely next month.
  • Adhara is the western-most star of the distinctive small triangle of stars beneath Sirius. At magnitude 1.5 I call it a first magnitude star, but others consider this second magnitude. So depending on how you count Adhara there are either 21 or 22 first magnitude stars.

Before leaving the Winter Hexagon, I must stress that  this is not simply a northern hemisphere show – if you live  in Sydney, Australia, you could just rename this the “Summer Hexagon.” I see these stars in the southeast – my friends in Sydney see them in the northeast of their sky – and, of course, since they’re “standing on their heads,” they see them a bit differently – something like this!

The “Winter Hexagon” becomes the “Summer Hexagon” in the Southern Hemisphere, but contains all the same bright stars. (Chart prepared from Starry Nights Pro screen shot.)

February Guidepost Stars

Of the stars mentioned so far, the two dog stars, Sirius and Procyon, plus the fence sitter, Adhara, are the guidepost stars to learn this month. They are the ones you can spot near the southeastern horizon, coming into view about 45 minutes to an hour after sunset. (We’ll have more to say about Regulus next month, and the other stars mentioned we’ve met in previous months.) To see the February guidepost stars – and the asterism of the Virgins –  look low in the southeast about 45 minutes to an hour after sunset.  Here’s what you should see.

Click image for larger version. This chart shows the three guidepost stars for February as they appear about an hour after sunset in the southeast. Sirius is the brightest star we see and Procyon is not far behind, but Adhara is not much brighter than its companions, which form a distinctive, small triangle the ancient Arabs knew simply as “the Virgins.” (Prepared from Starry Nights Pro screen shot.)

For a printer-friendly version of this chart, click here.

Procyon, the seventh brightest star we see, is first up in our sky, and thus the highest, of these three. To the southeast and a tad lower is brilliant Sirius, brightest star in our sky, and next to the North Star, Polaris, probably the best known star in the world. Adhara is the brightest star in the  “Virgins,” a simple,  distinctive  triangle asterism. But, of course, Sirius is dominant – far brighter than any other star we see in our night sky. I always think of Sirius as the eye of the great dog and as he sits, the triangle seems to be his rear haunches. From our perspective Adhara may be just another bright star, but of these three it is really the brightest by far – it’s just much farther away than the other two.  If we compared them side by side we would find that Procyon shines with the light of seven Suns, Sirius 23, and Adhara has a luminosity to the eye of 3,700 Suns! Now that’s bright.  And in another way, Adhara reveals our human bias, for if we had ultraviolet vision Adhara would be the brightest star in our sky, not Sirius. But again – that not the way we see it. From our perspective Sirius and Procyon are very bright because they are very close to Earth. Sirius, at a little more than eight light years is the closest star that we in the mid-northern latitudes see in our night sky. Procyon, at about 11 light years, is fourteenth on the list of nearest stars.  Most of the stars that are nearer than Procyon are also much fainter – in fact, too faint to see with the naked eye. If we count just those stars bright enough to see with the naked eye, Procyon is the sixth closest and Sirius is the second closest.  (The closest star, Alpha Centauri, is visible only to those in, or near, the Southern Hemisphere.) But Adhara? Adhara is 405  light years away – about the same distance as the North Star, Polaris. Sirius will frequently seem to be changing colors, but that’s just the effect of our atmosphere. Just as our atmosphere makes our Sun look red when it is rising or setting, it makes any bright star near the horizon appear to dance and change colors rapidly.

The Big Dog as Johannes Bayer depicted him in 1603. (Image courtesy of Linda Hall library of Science, Engineering and Technology.)
The Little Dog as shown in the 1603 Uranometria chart. (Image courtesy of Linda Hall library of Science, Engineering and Technology.)

Sirius is known as a “dog star” because it is the brightest star of the classic constellation, Canis Major – the Big Dog. Procyon is the brightest star in the constellation Canis Minor, the Little Dog. When you look at these constellations as depicted in early star charts, it’s hard to see how connecting the dots makes the stars take the forms the constellation’s name implies, but the images are still useful memory joggers.

Modern science, though, gives us even more reason to remember these two stars, or rather the faint companion stars that orbit them. These are designated Procyon B and Sirius B and they defy our ability to even imagine because there’s just nothing in our down-to-earth experiences that compare with these tiny stars.  One of these “pups”  – the one belonging to Procyon – is impossible to see with a backyard telescope and the other an extreme challenge.  The reason is they are quite dim and being very close to the bright stars, get lost in the glare.

But the mystery of these two fainter stars is that they are both white, indicating they are among the hottest of stars. So how could something be that hot, that close to us, and yet so dim? And the answer is more mind-boggling than the question – they are both white dwarfs, and white dwarfs are a class of stars far denser than anything we encounter on Earth. Now I always find talk of the density of stars counter-intuitive because it gets drilled into our heads that stars are gas and the gas we encounter in our daily lives is anything but dense!  In fact, it’s quite – well – gaseous!  To appreciate this, let’s take a close look at our own Sun.

Click image for larger view.Sirius – with Sirius B at lower left.  Credit: NASA, H.E. Bond and E. Nelan (Space Telescope Science Institute, Baltimore, Md.); M. Barstow and M. Burleigh (University of Leicester, U.K.); and J.B. Holberg (University of Arizona)

The Sun is a ball of gas which reaches densities that near the center are sixteen times that of lead!  That alone should stretch your mind. But now imagine the white dwarf. The stuff that makes up a white dwarf is about one million times denser than the stuff in the Sun.

Jim Kaler writes that if you had a billiard ball made up of the stuff of one of these white dwarfs it would weigh about 70 tons – roughly the weight of an M1 Abrams tank. (Think of what that would do to your pool table, not to mention your foot if it fell on it!)

We know this because we can calculate the mass of the stars by their orbit around their bigger, brighter companions. The result is, we end up with a mass roughly that of the Sun but a size roughly that of the Earth. You can fit one million Earths – and therefore one million white dwarfs – inside the Sun. (See why a white dwarf is one million times as dense as the Sun?)

How do you take all that mass and squeeze it down to such a small size? The physics of how that’s done goes way beyond me, but if you want to put a name to it, a white dwarf consists of “degenerate matter.” Unlike other stars, white dwarfs no longer burn with nuclear fires. In fact, they are no longer burning at all. They are the dying embers of stars – and in the case of the “pups,” the embers are being seen while still white hot. But they will eventually cool.

The name white dwarfs is given to this class of stars, but in truth not all white dwarfs are white – some can even be red. To make sense of this contradiction of terms, just think about an ordinary dying ember and how its color will change as it cools. So it is with these dying stars. Unable to generate any heat, what they radiate they lose.

This is also the ultimate fate scientists expect for our Sun.  As it eventually exhausts its nuclear energy, it will turn into a bloated red giant like Betelgeuse in Orion.  Later still it will blow off its outer shell of gases, turning into a planetary nebula, such as the Ring Nebula (M57) in Lyra.  And at the core of that nebula will be the dying ember we know as a white dwarf.

I’ve never seen the white dwarf that revolves around Sirius, but perhaps this season I will. Orbits are not circles, but ellipses. This means that sometimes there’s more distance between Sirius and its “pup” than at other times – and we happen to be in a period of several years when that distance will be growing, and so it will become easier to see the pup in a good, backyard telescope. (Sirius B completes an orbit around Sirius A in 50.2 years. Procyon B, while visible to professionals, is just simply too difficult a target for most backyard telescopes.) I also plan to take a close look at Adhara with a telescope, for it has a 7.5 magnitude companion just 7 arcseconds away. This should be a challenge – because of the difference in brightness of the two –  but not nearly the challenge that seeing the companion of Sirius. For those with binoculars and small telescopes, some of the most fascinating objects are in this general area of sky, near, or inside the Winter Hexagon, including the Pleiades, the great Orion Nebula, and the spectacular telescopic open clusters in Gemini and Auriga, M35, M36, M37, and M38. All that star light certainly can make for bright nights during the dark  of a northern winter.

Vital Stats for the Guidepost Stars

For Procyon:

  • Brilliance: Magnitude 0.38, the 7th brightest star in our sky. Shines with the luminosity of about 7 Suns.
  • Distance: 11.4 light years
  • Spectral Type: F
  • Position: 07h:39m:18s, +5°:13′:29″
  • Procyon B is magnitude 10.7 and orbits Procyon in 40.8 years.  It can be as close as 9 AU to Procyon (1 AU is the distance between the Earth and Sun), or as far as  21 AU.

For Sirius:

  • Brilliance: Magnitude -1.5,  the brightest star in our sky.  Shines with the luminosity of about 23 Suns.
  • Distance: 8.6 light years
  • Spectral Type: A
  • Position: 06h:45m:09s, -16°:42′:58″
  • Sirius B is magnitude 8.3 and orbits Sirius in 50.2 years. It can be as close as 8.1 AU to Sirius, or as far as 31.5 AU. (It will reach this greatest separation in 2019.)

For Adhara:

  • Brilliance: Magnitude 1.5, it has a luminosity to the eye of 3500 times that of the Sun! (In other words, much brighter, really, than Procyon or Sirius.)
  • Distance: 405 light years
  • Spectral Type: B2
  • Position: 06h:59m, -28°:59′:18″

Look North in February 2013 – Watch the Great Bear Come out of his Cave!

When you look to the northeast early on a February evening do you see this:

or maybe this:

Used by permission from the Linda Hall Library of Science, Engineering & Technology.

or perhaps this?

It all depends, of course, on your imagination, but for me I see something like the last image. Even that doesn’t quite capture what my imagination wants to do with these stars. What I see is a huge and rather grumpy bear, emerging from his cave a bit early after hibernating through a few rough months, and now he’s stretching – and clawing – his way up my sky, and he is magnificent!

But I admit, for years it wasn’t that way. I saw instead what I suspect many people see – the Big Dipper rising. And I knew, sort of vaguely, that this asterism – one of the most familiar in the world – was a major portion of the constellation of the Great Bear, Ursa Major.  But really, large as the Dipper is, it’s just the hind quarter of the Big Bear, which is really large, and when I finally took the time to trace out his head and ears and front and rear paws, he quickly became one of my favorite constellations – one of the rare ones like Orion and Scorpius that really look like what they depict.  And funny – I can’t explain why, but I seldom see it as a bear except at this time of year when it is rising. Then it seems to dominate my northern sky and my imagination.

Oh – did I say it looks like a bear? No – I should have said it looks like a bear no one has seen except in the sky – a bear with a long tail! I don’t know why that is. I assume it is because of the second depiction, which is how Johann Bayer pictured the Great Bear in his “Uranometria,” a breakthrough star atlas published in 1603.  Bayer was a lawyer, not a hunter. Maybe he had never seen a bear?

The first depiction, a Stellarium screenshot, is the best one to use as a guide for finding the correct stars. Besides the Dipper stars, there are a dozen more that trace out his main features, and all of these are either third magnitude, or on the brighter side of fourth magnitude – that is between 3.5 and 4, so they should be visible from most locations – assuming, of course, you are in mid-northern latitudes.  The chart that follows gives a view of the Bear in context with the rest of the northern sky in February.

About one hour after sunset, look north and you should see a sky similar to the one shown in our chart below. The height of Polaris, the North Star, will be the same as your latitude. Polaris stays put.  Everything else appears to rotate about it, so our view of all else changes in the course of the evening – and from night to night. It’s a good idea to check the north sky every time you observe to get a sense of how things are changing and to orient yourself.  Notice that the “W” now looks more like an “M” as it starts to roll on down into the northwest.

Click image for larger view. (Chart derived from Starry Nights Pro screen shot.)
Click here to download a printer-friendly image of the above chart.

Events in February 2012: Look West! Can you see the faintest – and the brightest?

Looking west this month after sunset offers a study in contrast. For one thing, the two brightest planets – in fact, the two brightest objects in our skies after the Sun and Moon – Venus and Jupiter, will be drawing together night-by-night until at the end of the month you could nearly cover the pair with your fist.

Why? Because in a very real sense we live in two worlds. One is the world of the ancients. The world they saw and we still see. In it the planets are wandering stars that  change positions in irregular patterns, while the fixed stars change position in our sky – but hold their positions relative to one another.

That is one world. It is an obvious world, but one many of us have lost touch with because our artificial light and homes hide the night sky from us.  The other world is the one revealed by the past four centuries of science.  In that world the planets are nearby, solid bodies, shining by reflected light and all revolving around a single star – our Sun. How they appear to us is governed by the laws uncovered by the work of Copernicus, Galileo, Kepler, and Newton.

To me the  fun is to live in both worlds – to appreciate the night sky as the ancients saw it – and at the same time to appreciate the night sky as revealed by the great minds of science.  And this February gives us a perfect opportunity to do so. For what really fascinates me is that the Jupiter and Venus show is the brightest part of two western light shows, one involving the largest object in our solar system after the Sun – Jupiter – and the other some of the smallest things we will see – the zillions of dust specs (roughly one millimeter in size) – that make up the Zodaical Light.

So when you are through being dazzled by photons reflecting off of huge bunches of stuff, relax, and see if you can find one of the most delicate reflection features of our solar system – in fact, one of the more subtle things you’ll ever see in the night sky – the Zodaical Light. It, too, is at its prime this month, but you need a genuinely dark sky, especially to the west, to see it.

Much more about that in a moment – but first the easy shot that goes on all month – the Jupiter and Venus Show!

This one you can’t miss, even if you live in a region where most of the stars are washed out by local light pollution. There’s a wonderful symmetry to this show and it’s so simple to see. Just go out about 45 minutes after sunset any night in February and look up in the southwest. Roughly overhead the brightest “star” you will see is Jupiter. And high in the west at this hour will be an even brighter “star,” Venus.

Venus is about six times brighter than Jupiter, but this difference may not be quite that obvious because Jupiter will be seen high in the sky where it has to get through less of our atmosphere – and the sky will be darker near Jupiter. Venus will still be basking against a twilight background.

There are subtle changes in the brightness of each planet as the month goes on. Venus starts the month at magnitude – 4.1. (Remember, the lower the magnitude number, the brighter the object.) By the end of the month it is magnitude – 4.3. Why? Well, in our travels – and it – about the Sun we get closer to it. At the start of the month we’re about 102,858,000 miles apart. At the end of the month this gap has closed to 85,002,000 miles.

That’s really significantly closer,so you might think the change in brightness would be even greater. However, as we draw closer to Venus, Venus is also inserting itself between us and the Sun and so we see less of it – that is, it goes through phases like our Moon and at the start of the month we’re seeing light reflected from 71% of its surface, while at the end of the month we’re seeing just 64% of its surface. (I’m indebted, by the way, to Sky and Telescope magazine which publishes all this data about the planets each month.)

Jupiter, since it’s orbit is well beyond us, doesn’t go through these dramatic phases. We see 99% of it at the start of the month and 99% at the end. But we are drawing apart – essentially the Earth in it’s much smaller orbit is quickly widening the gap between us and Jupiter – and that gap is much larger than the one between us and Venus, so even though Jupiter is much larger, it is so far away, it is still dimmer.

At the start of the month Jupiter shines at magnitude -2.3 and at the end of the month it is magnitude -2.2. That’s a change that will only be noticeable to those with lots of experience at evaluating brightness – to most of us, it will look the same. But in terms of distance Jupiter starts the month about 468,162,000 miles from us and by the end of the month this gap is 507,036,000 miles.

In other words Jupiter is nearly 40 million miles farther away, yet dims in light by just one-tenth of a magnitude.

I know these numbers might just be bouncing off your mind with a sense of irrelevancy, but they fascinate me simply because they reveal some of the inner gurglings of what are the constantly changing dynamics of our solar system – dynamics that result in us seeing in the night sky two very bright lights appearing to approach one another night-by-night.

Think of how that must have looked to people in other times when we didn’t spend so much time indoors, dazzled by artificial lights and we knew nothing about what these bright lights in the night really were, nor how they’re relationships changed as each moved about the Sun at different speeds in orbits of vastly different lengths.

And with that in mind let’s switch gears now and consider some very tiny objects that are orbiting the Sun as well and displaying a soft glow in our western sky as they do so.

Basking in the Zodiacal Light of Almost Spring

The last 10 days or so of February 2011 will be a good time to start looking for the Zodiacal Light.

Planets shine by reflected light, planets are found in the plane of our solar system – and thus in a certain section of sky, marked by the wide band of the zodiac – and so are these minute dust particles. They’re just hard to get your mind around because they don’t consist of the cloud of dust that is anything like our common experience of dust. That is, these dust particles are minute, but they are also far apart. So to get a picture of them, imagine a bunch of them about half the size of a BB shot and each separated from the other by about five miles! Five miles! That’s what we mean by “cloud” in this case.

But, of course, space is so huge and we’re so far from these dust particles that even with that separation, from our distance they look like a cloud and when the sun shines on them, this cloud creates a soft glow in our western sky.

You don’t need a totally clear horizon to see the zodiacal light, or binoculars, but you do need total darkness and that means little-to-no light pollution and no Moon. So you want to wait until a few days after full Moon to begin this quest. I feel I have a good shot at it from my favorite ocean-front observing point where I have a clear horizon to the west with no cities to create light domes there. Evenings in February and March – and mornings in September and October – are the best time for folks at mid-northern latitudes to look for this.

The zodiacal light is roughly the same intensity as the Milky Way, so if you can see the Milky Way from your chosen location, then you should be able to pick up this faint glow. Like the Milky Way, it stretches over a good deal of sky. It is widest near the horizon and gets narrower as it rises towards the zenith. You want to look for this roughly 80 minutes after sunset. You can check for an exact time for your location by getting information from here on when astronomical twilight ends. (The drop-down menu on that page specifies the times for astronomical twilight.) As astronomical twilight ends you want to start looking. As with any faint object, your eyes need to be dark adapted, so I am assuming you have been out for at least 15 minutes with no white light to dazzle you. If you try to look for this earlier, you may confuse it with twilight. Much later and it is not as bright, since what we are seeing is sunlight reflecting off interplanetary dust particles – dust particles that orbit in the same plane as the planets – the area we call the zodiac – and thus the name for this phenomena, zodiacal light.

If you see it, reflect on this more detailed explanation from Wikipedia:

The material producing the zodiacal light is located in a lens-shaped volume of space centered on the Sun and extending well out beyond the orbit of Earth. This material is known as the interplanetary dust cloud. Since most of the material is located near the plane of the Solar System, the zodiacal light is seen along the ecliptic. The amount of material needed to produce the observed zodiacal light is amazingly small. If it were in the form of 1 mm particles, each with the same albedo (reflecting power) as Earth’s Moon, each particle would be 8 km from its neighbors.

For the metrically-challenged (that includes me) that means about one dust particle every five miles! And that causes all that light?! Awesome!

Look North in February 2012 – Watch the Great Bear Come out of his Cave!

When you look to the northeast early on a February evening do you see this:

or maybe this:

Used by permission from the Linda Hall Library of Science, Engineering & Technology.

or perhaps this?

It all depends, of course, on your imagination, but for me I see something like the last image. Even that doesn’t quite capture what my imagination wants to do with these stars. What I see is a huge and rather grumpy bear, emerging from his cave a bit early after hibernating through a few rough months, and now he’s stretching – and clawing – his way up my sky, and he is magnificent!
But I admit, for years it wasn’t that way. I saw instead what I suspect many people see – the Big Dipper rising. And I knew, sort of vaguely, that this asterism – one of the most familiar in the world – was a major portion of the constellation of the Great Bear, Ursa Major.  But really, large as the Dipper is, it’s just the hind quarter of the Big Bear, which is really large, and when I finally took the time to trace out his head and ears and front and rear paws, he quickly became one of my favorite constellations – one of the rare ones like Orion and Scorpius that really look like what they depict.  And funny – I can’t explain why, but I seldom see it as a bear except at this time of year when it is rising. Then it seems to dominate my northern sky and my imagination.

Oh – did I say it looks like a bear? No – I should have said it looks like a bear no one has seen except in the sky – a bear with a long tail! I don’t know why that is. I assume it is because of the second depiction, which is how Johann Bayer pictured the Great Bear in his “Uranometria,” a breakthrough star atlas published in 1603.  Bayer was a lawyer, not a hunter. Maybe he had never seen a bear?

The first depiction, a Stellarium screenshot, is the best one to use as a guide for finding the correct stars. Besides the Dipper stars, there are a dozen more that trace out his main features, and all of these are either third magnitude, or on the brighter side of fourth magnitude – that is between 3.5 and 4, so they should be visible from most locations – assuming, of course, you are in mid-northern latitudes.  The chart that follows gives a view of the Bear in context with the rest of the northern sky in February.

About one hour after sunset, look north and you should see a sky similar to the one shown in our chart below. The height of Polaris, the North Star, will be the same as your latitude. Polaris stays put.  Everything else appears to rotate about it, so our view of all else changes in the course of the evening – and from night to night. It’s a good idea to check the north sky every time you observe to get a sense of how things are changing and to orient yourself.  Notice that the “W” now looks more like an “M” as it starts to roll on down into the northwest.

Click image for larger view. (Chart derived from Starry Nights Pro screen shot.)
Click here to download a printer-friendly image of the above chart.

Look East in February 2012: Two dogs rising in a star-spangled spectacular – the Winter Hexagon

We have two “dog stars” on the southeastern horizon early on February evenings  – Sirius and Procyon – and  both are part of what is certainly the brightest, star-spangled  section of our northern night sky – the Winter Hexagon.  Here’s how it looked to the camera of Jimmy Westlake who took this gorgeous shot of the Winter Hexagon over Stagecoach, Colorado, USA.  You may not see the faint band of the Milky Way shown here if you live in a light polluted region, but you certainly should be able to pick out the bright stars that outline the Hexagon, as well as the Pleiades star cluster visible near the top and just right of center.

Click on image for much larger view! (Copyright © 2007-2011 JRWjr Astrophotography. All rights reserved.)

Look carefully at that photo, then compare it with this star chart which is what we see from mid-northern latitudes as as we look southeast early on a February evening.

Click image for much larger version. To get the full beauty of this section of sky find an area with a clear horizon to the southeast and go out on a February evening a couple of hours after sunset. The chart shows what you’ll see. The link below provides a small black-on-white version you can print and take into the field. (Prepared from a Stellarium screen shot.)

For a printer-friendly version of this chart, click here.

People in the north tend to think that the stars are brighter in winter because the air is so cool and crisp. That certainly could be a factor. But the simple fact is our winter sky is dominated by a whole lot of very bright stars. In fact, there are 22 stars of first magnitude – 16 of which are visible from the northern hemisphere and more than half of these are visible in “prime time” on a February evening. And nearly all these bright stars are jammed into a space taking up less than one-quarter of the February night sky – that’s just one-eighth of the total night sky we can see through the year! Add to that the seven bright stars of the Big Dipper being dragged up the northeastern sky by the Great Bear on a February evening, and it is no wonder that in the dead of a northern winter our skies offer a lively, colorful, star-spangled spectacular.

The Hexagon alone contains seven of the first magnitude stars in our sky and an eighth that is the brightest second magnitude star we see – in other words, that one just misses being first magnitude by a hair. And nearby is Adhara, a star that sits right on the border between second and first magnitude; plus Regulus, another first magnitude star, is rising in the east. Whew! That’s a lot. Let’s review.  Going  counterclockwise and starting at the bottom, the Hexagon’s corners are marked by:

  • Sirius, the brightest, and at about eight light years one of the closest, stars in our sky – except the Sun, of course.
  • Rigel, the blue giant that marks one of Orion’s feet.
  • Aldebaran, the brilliant orange star that is the eye of Taurus the Bull and dominates the nearest open star cluster, the Hyades.
  • Capella, now high overhead, is really a complex of four stars that we see as one.
  • Castor and Pollux, the twins, one of which (Pollux) is first magnitude, while Castor is the brightest second magnitude star we see.
  • Procyon, the “Little Dog” star, which is dim only in comparison to Sirius, the “Big Dog.”

And . . .

  • Inside the Hexagon is another first magnitude star, Betelgeuse, the red giant that marks Orion’s shoulder, not to mention the three bright stars of Orion’s Belt – all second magnitude.
  • Regulus, the “Little King,” is a first magnitude star that is rising in the east and bringing us the familiar sickle of bright stars that mark the head of the lion. We’ll study it closely next month.
  • Adhara is the western-most star of the distinctive small triangle of stars beneath Sirius. At magnitude 1.5 I call it a first magnitude star, but others consider this second magnitude. So depending on how you count Adhara there are either 21 or 22 first magnitude stars.

Before leaving the Winter Hexagon, I must stress that  this is not simply a northern hemisphere show – if you live  in Sydney, Australia, you could just rename this the “Summer Hexagon.” I see these stars in the southeast – my friends in Sydney see them in the northeast of their sky – and, of course, since they’re “standing on their heads,” they see them a bit differently – something like this!

The “Winter Hexagon” becomes the “Summer Hexagon” in the Southern Hemisphere, but contains all the same bright stars. (Chart prepared from Starry Nights Pro screen shot.)

February Guidepost Stars

Of the stars mentioned so far, the two dog stars, Sirius and Procyon, plus the fence sitter, Adhara, are the guidepost stars to learn this month. They are the ones you can spot near the southeastern horizon, coming into view about 45 minutes to an hour after sunset. (We’ll have more to say about Regulus next month, and the other stars mentioned we’ve met in previous months.) To see the February guidepost stars – and the asterism of the Virgins –  look low in the southeast about 45 minutes to an hour after sunset.  Here’s what you should see.

Click image for larger version. This chart shows the three guidepost stars for February as they appear about an hour after sunset in the southeast. Sirius is the brightest star we see and Procyon is not far behind, but Adhara is not much brighter than its companions, which form a distinctive, small triangle the ancient Arabs knew simply as “the Virgins.” (Prepared from Starry Nights Pro screen shot.)

For a printer-friendly version of this chart, click here. Procyon, the seventh brightest star we see, is first up in our sky, and thus the highest, of these three. To the southeast and a tad lower is brilliant Sirius, brightest star in our sky, and next to the North Star, Polaris, probably the best known star in the world. Adhara is the brightest star in the  “Virgins,” a simple,  distinctive  triangle asterism. But, of course, Sirius is dominant – far brighter than any other star we see in our night sky. I always think of Sirius as the eye of the great dog and as he sits, the triangle seems to be his rear haunches. From our perspective Adhara may be just another bright star, but of these three it is really the brightest by far – it’s just much farther away than the other two.  If we compared them side by side we would find that Procyon shines with the light of seven Suns, Sirius 23, and Adhara has a luminosity to the eye of 3,700 Suns! Now that’s bright.  And in another way, Adhara reveals our human bias, for if we had ultraviolet vision Adhara would be the brightest star in our sky, not Sirius. But again – that not the way we see it. From our perspective Sirius and Procyon are very bright because they are very close to Earth. Sirius, at a little more than eight light years is the closest star that we in the mid-northern latitudes see in our night sky. Procyon, at about 11 light years, is fourteenth on the list of nearest stars.  Most of the stars that are nearer than Procyon are also much fainter – in fact, too faint to see with the naked eye. If we count just those stars bright enough to see with the naked eye, Procyon is the sixth closest and Sirius is the second closest.  (The closest star, Alpha Centauri, is visible only to those in, or near, the Southern Hemisphere.) But Adhara? Adhara is 405  light years away – about the same distance as the North Star, Polaris. Sirius will frequently seem to be changing colors, but that’s just the effect of our atmosphere. Just as our atmosphere makes our Sun look red when it is rising or setting, it makes any bright star near the horizon appear to dance and change colors rapidly.

The Big Dog as Johannes Bayer depicted him in 1603. ((Image courtesy of Linda Hall library of Science, Engineering and Technology.)
The Little Dog as shown in the 1603 Uranometria chart. (Image courtesy of Linda Hall library of Science, Engineering and Technology.)

Sirius is known as a “dog star” because it is the brightest star of the classic constellation, Canis Major – the Big Dog. Procyon is the brightest star in the constellation Canis Minor, the Little Dog. When you look at these constellations as depicted in early star charts, it’s hard to see how connecting the dots makes the stars take the forms the constellation’s name implies, but the images are still useful memory joggers. Modern science, though, gives us even more reason to remember these two stars, or rather the faint companion stars that orbit them. These are designated Procyon B and Sirius B and they defy our ability to even imagine because there’s just nothing in our down-to-earth experiences that compare with these tiny stars.  One of these “pups”  – the one belong to Procyon – is impossible to see with a backyard telescope and the other an extreme challenge.  The reason is they are quite dim and being very close to the bright stars, get lost in the glare. But the mystery of these two fainter stars is that they are both white, indicating they are among the hottest of stars. So how could something be that hot, that close to us, and yet so dim? And the answer is more mind-boggling than the question – they are both white dwarfs, and white dwarfs are a class of stars far denser than anything we encounter on Earth. Now I always find talk of the density of stars counter-intuitive because it gets drilled into our heads that stars are gas and the gas we encounter in our daily lives is anything but dense!  In fact, it’s quite – well – gaseous!  To appreciate this, let’s take a close look at our own Sun.

Click image for larger view.Sirius – with Sirius B at lower left.  Credit: NASA, H.E. Bond and E. Nelan (Space Telescope Science Institute, Baltimore, Md.); M. Barstow and M. Burleigh (University of Leicester, U.K.); and J.B. Holberg (University of Arizona)

The Sun is a ball of gas which reaches densities that near the center are sixteen times that of lead!  That alone should stretch your mind. But now imagine the white dwarf. The stuff that makes up a white dwarf is about one million times denser than the stuff in the Sun. Jim Kaler writes that if you had a billiard ball made up of the stuff of one of these white dwarfs it would weigh about 70 tons – roughly the weight of an M1 Abrams tank. (Think of what that would do to your pool table, not to mention your foot if it fell on it!)  We know this because we can calculate the mass of the stars by their orbit around their bigger, brighter companions. The result is, we end up with a mass roughly that of the Sun but a size roughly that of the Earth. You can fit one million Earths – and therefore one million white dwarfs – inside the Sun. (See why a white dwarf is one million times as dense as the Sun?) How do you take all that mass and squeeze it down to such a small size? The physics of how that’s done goes way beyond me, but if you want to put a name to it, a white dwarf consists of “degenerate matter.” Unlike other stars, white dwarfs no longer burn with nuclear fires. In fact, they are no longer burning at all. They are the dying embers of stars – and in the case of the “pups,” the embers are being seen while still white hot. But they will eventually cool.  The name white dwarfs is given to this class of stars, but in truth not all white dwarfs are white – some can even be red. To make sense of this contradiction of terms, just think about an ordinary dying ember and how its color will change as it cools. So it is with these dying stars. Unable to generate any heat, what they radiate they lose. This is also the ultimate fate scientists expect for our Sun.  As it eventually exhausts its nuclear energy, it will turn into a bloated red giant like Betelgeuse in Orion.  Later still it will blow off its outer shell of gases, turning into a planetary nebula, such as the Ring Nebula (M57) in Lyra.  And at the core of that nebula will be the dying ember we know as a white dwarf. I’ve never seen the white dwarf that revolves around Sirius, but perhaps this season I will. Orbits are not circles, but ellipses. This means that sometimes there’s more distance between Sirius and its “pup” than at other times – and we happen to be in a period of several years when that distance will be growing, and so it will become easier to see the pup in a good, backyard telescope. (Sirius B completes an orbit around Sirius A in 50.2 years. Procyon B, while visible to professionals, is just simply too difficult a target for most backyard telescopes.) I also plan to take a close look at Adhara with a telescope, for it has a 7.5 magnitude companion just 7 arcseconds away. This should be a challenge – because of the difference in brightness of the two –  but not nearly the challenge that seeing the companion of Sirius. For those with binoculars and small telescopes, some of the most fascinating objects are in this general area of sky, near, or inside the Winter Hexagon, including the Pleiades, the great Orion Nebula, and the spectacular telescopic open clusters in Gemini and Auriga, M35, M36, M37, and M38. All that star light certainly can make for bright nights during the dark  of a northern winter.

Vital Stats for the Guidepost Stars

For Procyon:

  • Brilliance: Magnitude 0.38, the 7th brightest star in our sky. Shines with the luminosity of about 7 Suns.
  • Distance: 11.4 light years
  • Spectral Type: F
  • Position: 07h:39m:18s, +5°:13′:29″
  • Procyon B is magnitude 10.7 and orbits Procyon in 40.8 years.  It can be as close as 9 AU to Procyon (1 AU is the distance between the Earth and Sun), or as far as  21 AU.

For Sirius:

  • Brilliance: Magnitude -1.5,  the brightest star in our sky.  Shines with the luminosity of about 23 Suns.
  • Distance: 8.6 light years
  • Spectral Type: A
  • Position: 06h:45m:09s, -16°:42′:58″
  • Sirius B is magnitude 8.3 and orbits Sirius in 50.2 years. It can be as close as 8.1 AU to Sirius, or as far as 31.5 AU. (It will reach this greatest separation in 2019.)

For Adhara:

  • Brilliance: Magnitude 1.5, it has a luminosity to the eye of 3500 times that of the Sun! (In other words, much brighter, really, than Procyon or Sirius.)
  • Distance: 405 light years
  • Spectral Type: B2
  • Position: 06h:59m, -28°:59′:18″

Coloring the stars – an exercise for all seasons

Trying to identify the true colors of stars, as we see them, is fun, challenging, and instructive.

Your assignment, should you choose to accept it, is to develop accurate color swatches that represent the colors of the bright stars, including our Sun, as they actually are seen and in so doing learn:

  • How to see color in the stars
  • What the color tells us about each star

The chart shows the Winter Hexagon because many of the brightest stars can be seen there all at one time, but it also includes swatches for several bright stars that are prominent in the spring, summer, and fall.

This image of the Winter Hexagon was taken by Jimmy Westlake looking at the skies over Stagecoach, Colorado. Look carefully and you can see color in some of the stars - especially if you click on the image to see the larger version. (Copyright © 2007-2011 JRWjr Astrophotography. All rights reserved.)

Star colors are real. They relate to a star’s temperature and from them we can surmise much more about a star. But they also are very subtle. I think of them not as colors, but as tints. I see stars essentially as white lights to which a little color has been added to tint it one way or another. I believe most people don’t see the colors at all when they first look at the stars and this can be frustrating, especially if you’ve read that Betelgeuse, for example, is an “orange” star.

With the naked eye you only will see color on the brightest stars because our eye simply needs a lot of light to detect color. In fact, point your binoculars at those bright stars, and you should find it easier to detect the colors because the binoculars gather more light. You can train yourself to see star colors, though people do differ in this ability. But for most, the colors are really quite obvious on some of the brighter stars, once you know what you can expect to see. And that’s what this little exercise is for – learning what you can expect to see.

Your main tools will be the chart and the color table provided here. You’ll have to provide the primary colors (red, yellow, and blue), plus white in some easily blendable medium, such as common water, tempera, or poster paints. Nothing fancy needed and no special painting skills required.

First, here’s the chart you will be coloring.

You can download a version for printing by clicking here.

And here’s the color table you will use as your guide

Your task is simple.

Next to each star on the star chart is its spectral classification. This consists of a letter and number. The letters go from blue to red stars in this order: OBAFGKM. Each letter gets divided into a numerical sub-classification from 0-9. So a “B0” star would be just at the beginning of the “B” category. A “B9” star would be at the end of that category and almost into the next one. The star chart shows the spectral classification for each star. Match that with what you see in the color table. Then determine its color.

You will notice that there are two different color scales in the table. That’s because the way we see color depends in part upon the environment in which we see it. The “conventional color” is what would be seen if the star were put under high magnification and projected onto a white sheet of paper in the daylight. The “apparent color” is what is seen by the naked eye in a dark sky. That is the color you want. That’s what you’ll try to duplicate by mixing your water colors and painting the swatch next to each star so it matches its classification – and thus what you are likely to see in the night sky.

The result will be a chart that will help you know what color to expect to see when you look at the stars in the sky. I should add that if you see a photograph of these stars, the colors will be similar, but different. That’s because the colors in a photograph depend on the color sensitivity of the film or computer chip used to record them – which is not the same as your eye. So you cannot use a photograph as an absolute guide to what you will see. The chart you make, if done well, will be a much better guide.

When you look for star color, make sure the star is high in your sky – hopefully at least 30 degrees or more above the horizon. All bright stars near the horizon will appear to flash many brilliant colors. Those colors – like the colors in our sunrises and sunsets – are caused by the Earth’s atmosphere. When you are looking at an object near the horizon, you are looking through much more air than when you are looking at a star high overhead.

Of course, you are going to have to use your judgment in making the color swatches, and you might experiment a bit on another piece of paper. That’s why I recommend using some sort of water color for this activity – so it’s easy to blend and thin your colors to get the color you want – the one that is closest to what you actually see. Of course to get orange you mix the yellow and red – and white will come in handy to lighten any of the colors.

Get the idea? Will your colors be perfect? I doubt it. But experimenting this way will give you a much better feel for how subtle star colors are and exactly what you are looking for when you go out at night. Too often people are confused and disappointed because they read that Betelgeuse or Aldebaran is a red or orange star – and when they read that, they are thinking of the conventional red or orange – quite naturally – but look at the chart and look at the difference between conventional colors and apparent colors.

More about a star’s spectral class

OBAFGKM is certainly a crazy order, I know. It started out to be an alphabetical list more than a century ago. But as they learned more about the stars, the letters got scrambled. Here’s an easy way to remember the order:

Oh Be A Fine Girl/Guy Kiss Me

At first they thought letters would be enough, but the more they learned about stars, the more they saw there were many subtle variations that were important. So for each letter there is a sub-classification system that goes from 0-9. Thus an O9.5 star, such as Mintaka, is in the “O” spectral class (blue) but about as close as one can get to being a “B” (blue white) star. Don’t be too concerned about these numbers, however. You’ll find it difficult enough just to get colors that accurately match the letter classifications. Besides, I’ve found that different sources sometimes give different numbers for the spectral classification of a specific star, so I see them as a good rough guide as to how solidly a star is into a specific class but not something to take overly seriously in terms of what we can detect with our eyes.

Mintaka, incidentally, is included here because bright “O” stars are hard to find. Mintaka was one of the easiest “O” star to identify, being the western-most star in Orion’s Belt. But coincidentally, Ainitak, the star at the other end of the belt, is also an”O” and  a bit brighter. But ay O9.7 it, too, just makes it into the “O” class by the skin of its teeth. In fact, it’s a bit closer to being a “B” star than Mintaka – but I guarantee you won’t see any difference.

“M” stars are even more difficult to find. True, Betelgeuse is one in the Winter Hexagon, and  in the summer we have another brilliant “M” star – Antares, the brightest star in the Scorpion.  But these are special. They both are Supergiants – stars that are going through their death throes and have expanded tremendously.  The vast majority of “M” stars are of average size, and in fact, these average-sized “M” stars are the most common stars in the universe – yet there is not a single “normal” class “M” star visible to our naked eye, let alone as bright as the stars that form the Winter Hexagon.

I also added our Sun to the chart. DO NOT LOOK AT THE SUN TO TRY TO DETERMINE COLOR. YOU WILL DAMAGE YOUR EYES. We were all taught as children to color our Sun yellow – and this is correct if you are talking about conventional color. But the Sun is a class G2 star, and I suggest you color its swatch the “apparent” color it would appear to our naked eye were we seeing it as just another bright star in our night sky. This means it would appear the same as Capella.

Binocular and telescope users can see many double stars, and some of these provide striking color contrast, such as the blue and gold of Albireo. Seeing two stars close together that are of different colors makes it even easier to see star colors but also presents a whole new set of challenges, and experienced observers frequently differ on what the colors of the double stars are. John Nanson has explored this in an excellent post to the “Star Splitters” blog that we co-author. To learn more about these stars and the special challenges of determining their colors, read John’s post here.

What we can surmise from the colors

As you can see from the temperature scale, blue stars are hot – red stars are “cool.” Cool, that is, as far as star temperatures go. They are still very, very hot: 3700 Kelvin is about 6,200 degrees Fahrenheit! (Steel melts at about half that temperature.)

So once you notice a star’s color, what more can it tell you about the star? A detailed answer is beyond this exercise, but it means you can make a very good guess about some other important characteristics of the star.

Here’s a summary in table form of what the spectral classification tells about the size and life expectancy of a star, and even hints at how it will probably die.

  • Ninety-five percent of all stars are on what is called the “main sequence.” Most of the stars that are not on the main sequence are white dwarfs. But a few others are giants or supergiants. Roughly one percent of the stars fall into one of the giant categories, such as Antares.
  • The lower limit for the mass of a star is 1/80th the mass of our Sun – or about 13 times the mass of Jupiter.
  • Temperatures are for a star’s surface. The interior is much hotter.
  • Age – “O” stars have short lives and thus die first, then “B,” etc. No “dwarf” “K” or “M” star has died yet – the universe isn’t old enough.

Events February 2011: A great “Luna-See” month, plus goodby Jupiter, hello Saturn and basking in the Zodiacal Light?

The apparent wobbling of the Moon shown here causes "librations" which result in our being able to see about 59% of the Moon, even though it always keeps the same face towards us. (This work has been released into the public domain by its author, Tomruen.)

 

 

February 2011: A Great “Luna-See” Month

What makes February 2011 a great “Luna-See” month? Well, the cycle of the Moon is pretty close to being in step with the calendar we all use this month. But the truth is, the Moon is special and always worthy of our attention if for no other reason than it is constantly changing, while most everything else in the sky stays the same – or takes more than a human lifetime to change noticeably.

What’s more, people just take the Moon for granted, and I find that even many experienced sky watchers either haven’t noticed – or can’t explain – some of the major motions of the Moon and why it is where it is at any given moment. So let’s engage in a little “Luna-See” this month and see if we can untangle in simple fashion the motions of the Moon and how these motions gives us a constantly changing show night-by-night and moonth-by-moonth!

No – that’s not a typo. A “moonth” is simply my term for the lunar cycle. Our months vary in length. But the lunar cycle – the time it takes to go from one New Moon to the next – is a constant 29.5 days. The Moon actually goes around our planet in 27.3 days – but by the time it completes one orbit our planet has moved along in its path around the Sun and the Moon has to play catch-up. To get to the position we call “New Moon” – the position where it is directly between us and the Sun – takes 29.5 days, or one “moonth!” ( OK, there’s a correct term for this – it’s called the “synodic month” or a “lunation.” It’s just that “moonth” makes more sense to me – maybe i should contact Mr. Webster 😉

Since 29.5 days is not the same length as our calendar month, the “lunations” get, well, out of sync with the calendar. But in February 2011 the New Moon occurs pretty close to the start of the month – February 3 – so that’s where we’ll start this little adventure in “luna-see.”

Ideally, this should be a three-pronged discovery adventure – first, attack the problem with your mind by reading this. But for me abstract descriptions don’t hold much water, so when you’re through reading what follows, I urge you to move on to:

The real fun, though, is to go out, look up at the Moon, and in your mind be able to picture the entire Earth/Moon/Sun tableau – to see those things that are out of sight and understand how they contribute to what is in sight – or more simply, to know why the Moon appears the way it does, in the place in our sky that it occupies at any particular moment. So let’s get started.

 

February 3, 2011, 2:31 UT – New Moon – Everyone Wants to See the New Baby!

Notice the precise time? That’s important for new Moon junkies who like to see what is the youngest Moon they can see. I’ve never been addicted to this game, but I’m a casual player. It’s fun and a challenge open to anyone. And a crescent Moon can be simply beautiful, especially if paired with some nearby bright planets. What you need is an unobstructed western horizon and very clear skies because when you’re looking for something near the horizon, you’re looking through a lot of air and even small clouds that build up over the course of distance to form a haze near the horizon.

The new Moon occurs when the Moon is between the Earth and the Sun. For February 2011 that is at 2:32 UT. (To convert Universal Time – UT – to your local time, go here, find your time zone, then use the chart on the bottom right of that page to see how many hours you should add or subtract for your time zone.) At new Moon we can’t see the Moon because the side facing us is unlit, and even if it were a tiny bit lit, it would be overwhelmed by the glare of the Sun. But because new Moon occurs so early in the Universal Time day, there’s a slim possibility some of us in North America and points west may see it on February 3 – it just depends on where we are – and, of course, the weather.

A young Moon with Jupiter about 30 degrees above it, as seen from 42°N 71°W about 45 minutes after sunset on February 4, 2011. Click image for a larger version. (Stellarium screen shot.)

People have reported seeing Moons as “young” as about 12 hours. A more realistic goal is a 20-hour Moon. Exactly how old the Moon is after sunset on February 3 or 4 – depends on your exact location. I’m roughly at 42°N, 71° W, and on February 3 right after local sunset the Moon will be about 18 hours old. If I’m real lucky I may see that – and if I do, it will be the youngest Moon I have seen. A much more realistic task is for me to look for it the next night, February 4. At sunset on February 4 at my location the Moon will be close to 40 hours old.

This looking for the first slither of Moon is a little game that’s fun to play. The sky is usually too bright for you to see it right after sunset. You have to wait a while – but the problem is, the longer you wait, the lower the Moon gets in the sky. So on the one hand, the sky is getting darker making it easier to see the Moon – but the Moon is getting lower making it harder to see! Binoculars help – but use caution. Wait until you are sure the Sun has set. You will be looking in the same section of sky for the Moon as the Sun just occupied, and you don’t want to accidentally view the Sun and burn your eyes!

In my case on February 4, 2011, the Moon sets almost two hours after the Sun. This means that about 45 minutes after Sunset – when the sky is getting pretty dark – the Moon will still be about 10 degrees above the western horizon and just a tad north (3 degrees) of where the Sun set – which, if I’m lucky and have really clear skies to the west – will be easy to see. On February 3 it’s a much different story. Even at sunset the Moon is only eight degrees directly above where the Sun set. (Remember, your fist held at arm’s length covers about 10 degrees.) But the Moon sets in just 45 minutes, so if I catch it at all, it will be while looking through a lot of air and against a bright background, and it will be a very dim sliver. My strategy will be to wait until about 10 minutes after sunset, then start scanning with binoculars.

 

February 11, 2011, 7:18 UT – First Quarter and a Close Encounter of the Pleiades Kind

This is the view on February 11, 2011, about 45 minutes after sunset for my location - 42° N, 71° W. The Moon passes about one degree beneath the Pleaides star cluster and you should be able to see both in the same binocular field of view, but the Pleiades will be washed out and dim because of the brilliant Moon light. Exactly how close the Moon is to the Pleiades depends on your location. Remember, it is constantly moving eastward - while at the same time, it, and all other objects in the sky, appear to be moving westward because of the rotation of the Earth. (Prepared from Starry Nights Pro screen shot.)

Now seeing the Moon is no challenge if your skies are clear. Each day at sunset it has moved about 12 degrees farther east as it circles the Earth. This means it’s climbing up our sky – on a slant, since it follows an arc across the sky, not a straight line – but higher each night. Tonight it will be about 70 degrees high about 45 minutes after sunset. And, of course, more and more of it is lit each night. Now we see about half of the Moon – that is half of what we will ever see, but really just one quarter of it. Nearly half of the Moon remains hidden to us all the time. This is because the Moon keeps the same face towards us. That is, it takes it just as long to spin once on its axis as it does for it to revolve once around the Earth. If the Earth did that as it journeyed around the Sun, half the Earth would be in constant sunlight, the other half in constant darkness! The other half of the Moon isn’t constantly dark, however. It does get sunlight on it, just as the half that faces us does – it’s just that the other half never faces us. Well, not quite – for various reasons we get little peeks at part of it, and when you add all these up we actually see about 59% of the Moon’s surface.

But as you look at the first quarter Moon in our sky, think about where it is at that moment – and more importantly, think about where the Sun is at that moment. The Sun moves about 15 degrees each hour. So if you are seeing the first quarter Moon about an hour after sunset, then the Sun is already about 15 degrees below your horizon. Can you picture it in your mind? Sort of like a huge flashlight, shining on and lighting half of it? Of course, you see only half of the lit portion, which is why this is called “First Quarter.”

For me, in the Eastern Time Zone of the US, first quarter Moon actually occurred at 3:18 am! So when I see it on the night of February 11 it’s about 15 hours later and the Moon is well on its way to being eight days old – it is past first quarter and a little more of it is lit. As I say, it is constantly changing – something you can see for yourself as you follow the “terminator,” the line between sunshine and darkness. Do this with binoculars a or telescope over the course of a few hours, and if you are a careful observer, you will see a difference.

The Moon is also about as far north as it will get this month – and thus almost as high in our sky as it’s going to get in February. Actually, for me it reaches its highest point a couple of hours after sunset on February 12 when it is 72 degrees high. Why? Because at that point in its travels around the Earth, it’s on the side where the Earth is leaning towards it – at least for us Northern Hemisphere observers. This is explained in detail in the projects:


 

February 18, 2011, 8:36 UT – Full Moon – Great for Lovers but Not Always Loved

Now here we are at full Moon - as illustrated by the "Luna-See" model.

Ah – the moment we’ve been waiting for – when we see the full face of the Moon – well, the full face that faces us is lit because the Moon is opposite the Sun in our sky. Focus on that word “opposite.” It’s very important for understanding the north-south motions of the Moon, and here’s a good thing to remember: The full Moon always rises directly opposite the setting Sun. This is most dramatic in June and December. Again, sticking to my own Northern Hemisphere as an example, the December Sun sets in the southwest – so the Full Moon in December rises in the northeast – directly opposite the setting Sun – not just on the other side of the sky, but in the other quadrant. And in June the Sun sets in the northwest, so the full Moon rises in the southeast. That summer full Moon mimics the path of the winter Sun – that is, it crosses our sky in a low arc to the south. And the winter full Moon? It mimics the path of the summer Sun and crosses our sky in an arc, high above us.

The abbreviated explanation for this is that the Moon goes through the same north/south motions in our sky every month – well, every “moonth” or lunation – that the Sun goes through every year. Why? It’s all because the Earth is tilted on its axis. The Sun is high in our sky when that tilt has us leaning towards it. It’s low when we’re leaning away from it. But we don’t change the way we lean – what changes is that we go around the Sun and so sometimes we’re leaning towards it, sometimes away from it. And the Moon? It goes around us each month. So sometimes it is on the side of us that leans towards the Moon, and thus it’s high in our sky, and sometimes it’s on the side that leans away from it.

Again – this explanation may be sufficient for you, but if not, I urge you to build the simple models and explore these motions on your own. You should find it much easier to get the geometry clear in your mind if you do the projects.

The full Moon is, of course, a beautiful sight – but amateur astronomers won’t always agree. For them – especially if they use telescopes – the full Moon is a bother. If you look at the Moon with your telescope, it is rather uninteresting because the sunlight is shining straight down on it and so there are no shadows to indicate how high a lunar mountain is or how deep a lunar crater. Worse yet, the Moon is so bright, its light is washing out many of the other fine telescopic sights that the night sky holds.

However, sky watchers just learning the bright stars may welcome a full Moon because the sky is less confusing. Instead of seeing a couple of thousand stars – which can be very confusing – they see only the brightest stars, and these are easier to get straight.

During the first half of the lunation – the “moonth” – the Moon is in the sky right after sunset. As it went from new Moon to full, it got higher in the sky each night and it stayed with us longer, setting roughly about 50 minutes later each night. By the time it was full, the Moon rose as the Sun set, then set in the early morning, just before the Sun rose.

 

February 24, 2011, 23:26 UT – Last Quarter Fun for Insomniacs and Early Risers

Last quarter Moon rises in the southeast near the bright star, Anatares, in the early morning of February 26. Here's how it would appear at about 2:30 am EST from 42°N 71°W. Click image for much larger version. (A Stellarium screen shot.)

OK, last quarter is not the same as first quarter. I say that with emphasis because I see too many books that treat the Moon in detail from new Moon to full Moon – then dismiss the second half of the cycle as if it were just a repeat of the first half. Anyone who believes that’s the case is guilty of what Holmes accused Dr. Watson of when he said: “Quite so . . . you see, but you do not observe.”

Top image shows how the waxing Moon reveals the Sea of Crisis on its eastern limb as sunrise moves from east to west across the Moon. In the second half we see the Moon a few days after full when it has started to wane. Notice that it shuts down the eastern side first - the Sea of Crisis was the first major sea revealed and it is the first major sea to return to darkness as the sunset line moves from east to west across the Moon.

On a broad scale, to the naked eye, things are happening in reverse during the second half of the”moonth.” The first crescent Moon we see a few days after new Moon reveals a beautiful, round sea – Mare Crisium (Sea of Crisis) – near the Moon’s eastern limb. After full Moon, this will be the first area to go dark.

Yes, at last quarter we are seeing just half of the face of the Moon again, but this time the Sun is coming from the other direction. From new Moon to full Moon the Sun is rising. The terminator – the line between darkness and light – marks the sunrise point on the Moon. This change becomes most obvious when viewing with binoculars and small telescopes, for it means that when a crater is highlighted it is the inside, western wall of the crater that is lit and the outside eastern wall of the same crater. From full Moon to new moon, that sequence is reversed. Now the same crater will have the inside of its eastern wall lit and the outside of its western wall. So what? So things have a different feel. Seeing is our most powerful sense – but we also tend to take things for granted – take a “been there, seen that” attitude, and the result is that in the fine words of Holmes, we see, but we do not observe.

When you observe the Moon carefully, you will notice that many familiar features look quite different during the second half of the lunar month. In fact, I frequently find myself disoriented when I look at the Moon in its waning phases. I have to go to my charts to be sure I know what I am looking at because sometimes very familiar craters and mountain ranges look quite different under the different lighting.

All of this should be clear if you simply stop and think for a moment about where the major players are – where the Moon is at the moment and where the Sun is at the moment. When we did this with the waxing crescent Moon we knew the Sun was below the western horizon. With the waning crescent Moon the Sun is below the eastern horizon, throwing its light from the west side of the Moon towards the east. That’s the opposite of what it was doing with the waxing crescent Moon.

Since the Moon comes up about 50 minutes later each night, it is not long after the full stage that the Moon isn’t visible in the night sky until several hours after sunset. By the last quarter it’s generally not visible until after midnight. And the waning crescent Moon rises just a few hours ahead of the Sun.

This, of course, means that if you want to observe the Moon during these later phases you need to either get up early – or not go to bed. That works for insomniacs, but is difficult for the schedule of most people.

 

The Moon in Daylight

From time to time someone comes to me quite surprised that s/he saw the Moon in daylight. Yes, you can see it in daylight. It is visible most days. It is just not obvious. And some days are better than others if you want to look for the Moon in daylight. At new Moon and full Moon the Moon is not likely to be visible in daylight. The rest of the time it is – you just have to know where to look and have, of course, clear skies. And you have to be prepared to see a pale shadow of what you see at night – although I must say it can be quite bright and impressive when near the first quarter or last quarter stages and when seen within a few hours of sunset or sunrise when the section of the sky the Moon occupies is still comparatively dark.

So here are a few good times to see the Moon during the day in February 2011.

February 11-15, 2011 – This is when the Moon is waxing between first quarter and full. Two hours before sunset – until sunset – look for the Moon high in the east. On each successive day it will be lower in the eastern sky at that time, but more of it will be lit. By full Moon it is below the eastern horizon until near the time of sunset.

February 20-24, 2011 – This is when the Moon is waning between full and last quarter. Look for it high in the western sky from sunrise until a couple of hours after sunrise. With each successive day the Moon will get smaller, but higher in the western sky.

At either end of the “moonth” the Moon is in a crescent phase and near the Sun. While it is in the daytime sky much of the day, it is very difficult to see and looking for it with binoculars or a telescope at such a time would be dangerous since you could accidentally look at the Sun instead and damage your eyes. That’s why we look for the crescent Moon in the hour or so after sunset, or the hour or so before sunrise.

 

Goodby Jupiter, Hello Saturn!

Not quite. Saturn has been with us for months, but only in the morning sky. And Jupiter will still be with us in March, but it will be getting too low in the west to observe it easily. So in practical terms, this will be the last month to get a real good look at Jupiter and its dancing Moons with binoculars or a small telescope. And it will be the first month that Saturn will get high enough in the sky before midnight to get a good look at this most beautiful of planets – most beautiful, that is, for those using a small telescope. I’m afraid Saturn’s rings are not within the reach of those using binoculars, and it’s the rings that make this planet so astonishing. Even when you know exactly what you will see, the 3-D impact of those rings going around the planet are a sight you will never forget, so if you get an opportunity to see Saturn in even the smallest telescope, do take that opportunity.

Finding Jupiter should not be an issue – simply look for the brightest “star” in the west southwest. The only real star you could confuse it with is Sirius – and Sirius will be dimmer and half a sky away in the southeast at that time. About an hour after sunset Jupiter will be about 30 degrees above the horizon – certainly easy to see and view with binoculars or a small telescope. But it sets about four hours after sunset and long before that it will become difficult to view. By the end of the month it will be about 13 degrees above the horizon an hour after sunset and will set in another hour or so. It will make a pretty sight in the southwestern twilight sky to the naked eye but will not be a good target for binoculars and telescopes when that low.

Saturn, however, is a good replacement, making another bright “star” for anyone to pick up with the naked eye and a wonderful sight for the small telescope user.

To find Saturn you need to wait until about six hours after sunset at the start of the month, then look south of east. By the end of the month this is the scene about four hours after sunset. Click image for larger view. Chart is for those in mid-northern latitudes. (Prepared from Starry Nights screen shot.)

To find Saturn you look east about six hours after sunset at the start of the month – four hours by the end of the month. To the north of east you should see brilliant Arcturus rising and a bit higher than Saturn. It also is about half a magnitude brighter. Saturn will have a slight yellowish cast and be a bit south of east. The two will be the brightest stars in that section of sky at the time, although in less than an hour they will be joined by Spica, a bit dimmer than Saturn and just below it.

Venus continues to dominate the morning sky to the southeast, but it is starting to get close to the Sun. It rises about three hours before the Sun at the start of the month – two hours before sunrise by the end of the month. Can’t be missed, though. At magnitude -4.2 it’s about twice as bright as Jupiter and will be outshone only by the Moon and the Sun. On February 28 and March 1, Venus will make a nice pairing with the waning, crescent Moon.

 

Basking in the Zodiacal Light of Almost Spring

The last 10 days or so of February 2011 will be a good time to start looking for that most elusive of Solar System sights, the Zodiacal Light.

Now this is something much different. You don’t need a totally clear horizon to see the zodiacal light, or binoculars, but you do need total darkness and that means little-to-no light pollution and no Moon. So you want to wait until a few days after full Moon to begin this quest. I feel I have a good shot at it from my favorite ocean-front observing point where I have a clear horizon to the west with no cities to create light domes there. Evenings in February and March – and mornings in September and October – are the best time for folks at mid-northern latitudes to look for this.

The zodiacal light is roughly the same intensity as the Milky Way, so if you can see the Milky Way from your chosen location, then you should be able to pick up this faint glow. Like the Milky Way, it stretches over a good deal of sky. It is widest near the horizon and gets narrower as it rises towards the zenith. You want to look for this roughly 80 minutes after sunset. You can check for an exact time for your location by getting information from here on when astronomical twilight ends. (The drop-down menu on that page specifies the times for astronomical twilight.) As astronomical twilight ends you want to start looking. As with any faint object, your eyes need to be dark adapted, so I am assuming you have been out for at least 15 minutes with no white light to dazzle you. If you try to look for this earlier, you may confuse it with twilight. Much later and it is not as bright, for what we are seeing is sunlight reflecting off interplanetary dust particles – dust particles that orbit in the same plane as the planets – the area we call the zodiac – and thus the name for this phenomena, zodiacal light.

If you see it, reflect on this explanation from Wikipedia:

The material producing the zodiacal light is located in a lens-shaped volume of space centered on the Sun and extending well out beyond the orbit of Earth. This material is known as the interplanetary dust cloud. Since most of the material is located near the plane of the Solar System, the zodiacal light is seen along the ecliptic. The amount of material needed to produce the observed zodiacal light is amazingly small. If it were in the form of 1 mm particles, each with the same albedo (reflecting power) as Earth’s Moon, each particle would be 8 km from its neighbors.

For the metrically-challenged (that includes me) that means one dust particle every five miles! And that causes all that light?! Awesome!

 

Algol takes a Dip, or Two, or Three

I wrote about Algol the “Demon Star” in the posting for October, but it’ s still well placed for viewing in February, and if you look at the right time, you’ll catch it in mid-eclipse, which is cool.

Every 2.3 days Algol dims like clockwork, but it is only at its dimmest for about two hours, so to see it in this condition you really need to be watching at the right two hours. Fortunately, there are several places that will give you a list of times when this occurs – but many of them will be while normal people are sleeping – and many more will be during daylight hours. However, each month there should be one or two dates when it is really a good time for you to catch Algol doing its thing.

Most of the listings I know of for Algol “minima” give date and time in Universal Time. What I like about the one at Sky and Telescope magazine, is it will calculate a list of coming Algol minima for you – and give you the Universal Time, plus your local time. So it’s easy to glance over it and see when it will be most convenient – weather permitting – for you to take a look. In my case, February 2011 gives me a couple of opportunities worth noting:

  • 02/09/2011 @ 10:18 pm
  • 02/12/2011 @ 07:07 pm
  • 03/04/2011 @ 08:53 pm

Yes, that last one is for March, but why not plan ahead a little – with winter weather it’s easy to get clouded out, so the more opportunities the better your chance of seeing something. I find these eclipses amazingly elusive and rarely see one, maybe because I think there’s always going to be another opportunity.

 

Also new this month:

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