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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 October 2014! See a bow, the demon star, and a distant galaxy

On tap this month are:


To begin our monthly exploration of the night sky in the east, you can take a slide down Andromeda’s Couch to Mirfak and the Bow of Perseus in the northeast – that is, you can if you learned how to find Andromeda’s Couch last month. If that’s new to you, ignore it for now and simply start by looking for the “Bow” of three bright stars rising low in the northeast.

To find it, go out about an hour after sunset and watch the bright stars emerge. It may take a few minutes to see the bow clearly, but what you are looking for is three stars in a vertical arc, with the middle one – Mirfak – the brightest. How big an arc are we talking about? Just make a fist and hold it vertically at arm’s length, and your fist should just cover these three stars. How high? The bottom one should be about a fist above the horizon. Here’s a chart modified from Starry Nights Pro software.

Click image for larger version. (Derived from Starry Nights Pro screen shot.)

Click image for larger version. (Derived from Starry Nights Pro screen shot.)

Click image for larger version. (Derived from Starry Nights Pro screen shot.)

For a printer friendly version of this chart go here.

The bow asterism is the core of the constellation Perseus. Now if you want to be a stickler about mythology, Perseus usually is not depicted with  a bow – he wields a sword instead, which he is holding in his right hand high over his head, while in the left hand he holds the severed head of Medusa. Here’s how the 1822 “Urania’s Mirror” depicted him.

perseus
Perseus – click for a larger version.

Oh boy – and if you can see all that in these stars, then you have a very vivid imagination. I never would have learned the night sky if I had to try to trace out these complex constellations as imagined by ancient cultures and depicted in star guides up until fairly recently. And for the purposes of helping you find your way around the night sky I think remembering the “Bow of Perseus” is easier.

Getting sharp about brightness

As you start to learn the stars, it may surprise you how precise you can be about their brightness. At first you may have difficulty just telling a first magnitude star from a second, but if you get to know Algol, the “Demon Star,” I bet you’ll find that you can quickly become quite sophisticated in assessing brightness and shaving your estimates down to as little as a tenth of a magnitude. So let’s take a closer look at the Bow and three bright stars in this region – Mirfak, Algol, and Almach.

Imagine a star that regularly varies in brightness every few days – that’s what Algol does. Exactly every 2 days, 20 hours, and 49 minutes it begins a 10-hour period where its brightness dims more than a full magnitude. If you look during the right two hours, you’ll catch it at or near its dimmest – and most of the rest of the time you’ll catch it at or near peak brightness. And it’s quite easy to judge. But first let’s find it. Here’s the chart we’ll use.

Notice how Algol makes a very nice triangle with two companions, and all three stars are close to the same brightness – Almach, the northern-most star in Andromeda’s Couch; Mirfak, the central star in the Bow of Perseus; and Algol. Algol is called the “Demon Star” because it varies in brightness – and, of course, it marks the head of Medusa. Gazing directly at her turned onlookers to stone according to Greek mythology – but I hope that doesn’t worry you because I’m going to ask you to stare directly at her – or at least at Algol! In fact, that relates to our first challenge: Go out any clear night and study these three stars and decide which is the brightest. Two are equal in brightness, but one is a tad brighter than the other two. Which is it? Algol? Mirfak? Almach? (The answer is at the end of this post so you can ignore that answer until you actually have an opportunity to test yourself.)

However . . .

Because Algol is a variable, sometimes when you look at it, Algol will actually be significantly dimmer than either Mirfak or Almach. In fact, there’s a reasonable chance it will be dimmer than either of Mirfak’s two fainter companions that make up the Bow of Perseus. If, when you test yourself, this is the case, congratulations! Make note of the date and time. But that’s not the test – just fun! For the test you want the “normal” condition, which has these three nearly the same in brightness.

OK? Back to Algol. It’s a special kind of variable star known as an eclipsing binary. That is, what looks like one star to us is really two stars very close together, and when we see Algol’s light start to dim it means its companion is passing between Algol and us causing an eclipse. Since the stars are locked in orbit around one another this happens with clockwork regularity.

algol_edu

The above diagram came from this astronomy class web site which includes a more detailed scientific explanation. Since either star of the pair can cause an eclipse, there is a much fainter, secondary eclipse of Algol – really too faint to be noticed by most observers. Why is one eclipse fainter – because one star is blue and much hotter/brighter than the other star. It is when the cooler star is in front that we see the dramatic change in light.

It’s fun to catch Algol in mid eclipse, but I suggest you not read about when to do this right now. Instead, do the little challenge first. Then when you’re ready, go to the final item in this post, which explains how and when to catch Algol in eclipse and in the process, tells you the brightness of its companions.

See a few hundred billion stars at one glance!

Yes, you can do it if you have good dark skies, you have allowed your eyes to dark adapt, and you are looking at the right place. Once again, Andromeda’s Couch is our guide, and what we are looking for this time is the Great Andromeda Galaxy aka M31.

This is our “neighbor” in space if you can wrap your mind around the idea that something “just” 2.5 million light years away is a “neighbor.” As you try to do that remind yourself that a single light year is about 6 trillion miles – of course, good luck if you can imagine a trillion of anything! OK – let’s try that – quickly. If you wanted to count one million pennies, and you counted one every second, it would take you 11 days. A billion pennies would take you about 31.7 years! And a trillion pennies? 31,700 years – roughly the time that has elapsed since the earliest cave paintings. So what if you were the cabin boy on an inter-galactic spaceship charged with ticking off the miles at the rate of one mile a second on the way to Andromeda? Think you could do it? Think you would live long enough? Hardly! The task – and journey – would take you almost half a million years – or by my crude estimate 475,650 years! And that’s non-stop counting. Ohhh – are we there yet, Mom?

And yet here you are collecting photons in your backyard that got their start on the journey to your eyes some 2.5 million years ago! Even if you live under normal, light-polluted skies, you should be able to see the Andromeda Galaxy with binoculars. In fact, this is one object where the binocular view can be as rewarding as the view through a telescope. Here’s a wide field chart for mid-month and about 90 minutes after sunset. At that point the galaxy should be roughly half way up your eastern sky. (Look for it on a night when the moon isn’t in the sky and when, of course, your eyes have had at least 15 minutes to dark adapt.)

Click image for larger version.

Starting with the preceding chart – and moving to the chart below, here’s a more detailed star-by-star hop to the Andromeda Galaxy:

  1. Locate the Great Square
  2. Locate Andromeda’s Couch off the northeast corner of the Square.
  3. Go down to the middle star in the couch, then count up two stars and bingo!
  4. You can also find the general vicinity by using the western end of the “W” of Cassiopeia as if it were a huge arrowhead pointing right at the Andromeda Galaxy.

Well, “bingo” if you have been doing this with binoculars. With the naked eye it’s more an “oh yeah – I see it – I think!” But what do you expect? Think about it. The light from the near side of this object started its journey about 150,000 years before the light from the more distant side did! And think of where the human race was 2.5 million years ago when these photons began their journey – or for that matter, where all these stars really are today! Nothing is really standing still – everything is in motion.

You might also want to think about the folks who are on a planet orbiting one of those stars in the Andromeda Galaxy and looking off in our direction. What will they see? A very faint patch – certainly  fainter than what we see when we look at the Andromeda Galaxy, but in a modest  telescope  roughly similar in shape, though about two-thirds the size. Both Andromeda and the Milky Way Galaxy we inhabit are huge conglomerations of stars. We’re about 100,000 light years in diameter – Andromeda is about 150,000 light years in diameter. The Milky Way contains perhaps 100 billion stars – the Andromeda Galaxy maybe 300 billion. (Don’t quibble over the numbers – even the best estimates are just estimates. )

And yes, in a few billion years we will probably “collide” with the Andromeda Galaxy, for we are hurtling towards one another. Such galaxy collisions are not that unusual and probably aren’t as violent as the word “collision” makes them sound – but they do, in slow motion, bring about radical changes in one another.

But all that is for the professional astronomers to concern themselves with – for us, there’s the simple beauty and awe of knowing that with our naked eye – or modest binoculars – we can let the ancient photons from hundreds of billions of stars ping our brains after a journey of millions of years.

So here’s hoping for clear skies for you so you can find a winking demon and capture in your own eye the photons from a few hundred billion stars in the Andromeda Galaxy!

And now the truth about Algol and companions

Have you done the Algol test yet? Looked at Algol, Mirfak, and Almach and tried to decide which is brightest? If so, you can check your answer by continuing to read. If not, I suggest you first do that exercise, then come back to this.

Chances are that when you look at Algol, it will be at its brightest – but how can you tell? Well, as we mentioned, you can compare it to Mirfak – but there’s an even closer match with another nearby bright star – Almach. That’s the third star in Andromeda’s Couch – the one nearest Algol.

Mirfak is the brightest of the three at magnitude 1.8.

Almach is magnitude 2.1 – which is the same brightness of Algol when Algol is at its brightest – which is most of the time. OK – for the hair splitters, Almach is a tad dimmer than Algol, but the difference is far too little to be able to tell with your eye. But that makes Mirfak about one third of a magnitude brighter than the other two. That difference you should be able to see – but it does take practice.

Here’s a chart showing the magnitude of the stars near Algol that you can use to compare it to and see if it is going through an eclipse. People who look at variable stars use charts like this, but with one important exception – the numbers are given like they were whole numbers so you will not confuse a decimal point with another star. Thus, a star like Mirfak, of magnitude 1.8, would have the number “18” next to it. I broke a convention here because there are just a few bright stars on the chart, so I didn’t worry about the possible confusion of a decimal point being mistaken for another star.

So If Algol and Almach are the same, no eclipse is going on at the moment. If Algol appears dimmer than Almach, then an eclipse is in progress. If it’s as dim or dimmer than either of the companions of Mirfak in the Bow, then you can be pretty sure you’ve caught Algol at or near its darkest. In two hours – or less – it will start to brighten and will return to full brightness fairly quickly.

Catching Almach at its dimmest is fun, but not as easy as it may seem. Why? Because although an eclipse happens every few days, it may happen during the daylight hours, or in the early morning, or some other time when it’s inconvenient. And, of course, you need clear skies. So when I want to observe an Algol eclipse, I go to a handy predicting tool on the Web that you can find here.

I then note the dates and times and pick out only those dates when the times are convenient to me – that is, happening during my early evening observing sessions. Then, given the iffiness of the weather, I consider myself lucky when I  get a good look at an eclipse of Algol. What are your chances – given your weather – that it will be clear on a night when an eclipse is visible before your normal bed time?

Algol starts to noticeably dim about two hours before mid-eclipse and is back to almost full brightness two hours after mid-eclipse.

Using the Sky and Telescope Algol calculator for October 2014 I find that  just  one hits at a good time for me  – October 13, 9:25 pm EDT

Of course the dates and time may be different for you, depending on where you live, and none of us can escape the whims of the weather!

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Look North in October 2014 – and find a really bright star!


Click image for larger view. (Prepared from Starry Nights Pro screen shot.)

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

When I say “really bright,” I mean Capella – and I say it because so many folks assume, quite understandably, that the North Star will be the brightest in that section of the sky. It isn’t.

Capella is one of our brightest stars, and you may catch it this month just peeping up over the northeastern horizon about an hour and a half after sunset. And it is brilliant!  When you see Capella,  compare it with the North Star  and you will get a good idea of what the word magnitude means. There are a solid two magnitudes difference between the two – or if you want to get technical, Capella is magnitude 0 and Polaris is magnitude 2.

Yes, the magnitude system goes backwards – the lower the number, the brighter the star. Each magnitude difference represents a change of about 2.5 times in brightness. So a zero magnitude star is 2.5 times as bright as a first magnitude star – and 2.5 x 2.5, or 6.25 times as bright as Polaris, a second magnitude star. And while we’re on this subject, the faintest star in the Little Dipper – it’s over in one corner of the cup – is just about magnitude five. That means Capella is 100 times as bright as that star. (OK – if you actually do the math it doesn’t come out because I rounded off the difference – it’s really 2.512 for those wanting more precision.)

In fact, there is another interesting way to look at that star – at magnitude 4.9 it is almost exactly what our Sun would look like if it were placed just 32.5 light years away. At that distance our sun would be magnitude 4.8 – and that distance is the distance we use to compare stars. That is, to get an “absolute magnitude” for them so we can compare apples with apples,  we ask ourselves how bright a star would be if it were 32.5 light years from us.

And while we’re on the subject of magnitude, the Little Dipper does give us a great range. Polaris, as we said, is magnitude 2. The other bright star in the Little Dipper is magnitude 2 also – it’s at the end of the cup away from Polaris. Sharing that end is a magnitude 3 star, and these two are known as the “Guardians of the Pole” as they are prominent, close, and like other stars, circle around the pole  every 24 hours. Most of the other stars in the Little Dipper are magnitude 4, with the one star in the far corner of the cup being magnitude 5, as noted – well, actually 4.9. There’s a chart with these magnitudes in this post. Many people who live in light-polluted areas can see only three stars in the Little Dipper – Polaris and the two Guardians of the Pole.

How faint a star can you see? Depends upon your eye sight, the light pollution in your area, the transparency of the skies on any given night, how high the star is in the sky, and, of course, your vision and dark adaption. But as a general rule of thumb magnitude 6 has been accepted as the typical naked eye limit. However, if you live in a typically light polluted suburb you may see only to 4, or worse yet, magnitude 3. And observers on mountain tops with really clear skies reliably report seeing stars as faint as magnitude 8. All of this is with the naked eye. Add ordinary binoculars and you will certainly add three to five magnitudes to the faintest star you can see. In fact, you take a huge jump in the number of stars seen just by using binoculars with 50mm objective lenses. That’s why many amateur astronomers with fine telescopes also are likely to have a pair of 10X50 binoculars that they keep handy. I always did, but more recently I stumbled upon some very inexpensive Celestron 15X70 binoculars that I love for quick peaks, though they are two powerful and large to hold steady for serious observing.

For more serious work I now use relatively expensive 10X30 image stabilized binoculars. Yes, the 30mm means they do not gather nearly as much light as the 50mm standards – but the image stabilization means they take better advantage of the light they do gather. They’re also more compact and light, so I  don’t mind carrying them for several hours.

Capella will be a “look east” guide star next month, but you can get to know it this month as you look north. And if you live in mid-northern latitudes, it will become a most familiar site. In fact, where I live – about latitude 42°N – it is in the night sky at some time every night of the year. This is because it is so far north that as it circles Polaris, it only dips below the horizon for a few hours at a time.

Sky, Eye, and Camera: Special Opportunities for October 2014

Note: This is a new feature about events each month that are not only fun to observe with eye and binoculars, but are particularly suitable for capture as photographs –  especially photographs that convey a sense of being there and are taken with ordinary cameras.   While taking night sky photographs used to be more demanding, modern digital cameras don’t have to go to bed at night – they’re a great addition to your night sky enjoyment. Greg Stone

September 2013 - Full Moon rises shortly after Sunset with the Earth's shadow as backdrop, topped by the rosy "Belt of Venus." This shot was easy because the Moon is so bright.  But on October 8, 2014 I expect a similar situation in the morning western sky just before Sunrise. However, in that case the Moon won't simply be in line with the Earth's shadow - it will be in it, fully eclipsed. Under such circumstances will be able to see it?

September 2013 – Full Moon rises shortly after Sunset with the Earth’s shadow as backdrop, topped by the rosy “Belt of Venus.” This shot was easy because the Moon is so bright. But on October 8, 2014 I expect a similar situation in the western sky just before Sunrise. However, in that case the Moon won’t simply be in line with the Earth’s shadow – it will be in it, fully eclipsed. Under such circumstances will we be able to see it?

Photographing October’s Lunar Eclipse

The moon makes all sorts of news this month, but for U.S. East Coast dwellers such as me the big photo opportunity will be the total Lunar eclipse on the morning of October 8, 2014.

In addition, much of North America will see a partial solar eclipse as the Moon’s shadow falls on the Earth October 23. On October 17 and 18 the Moon plays tag with brilliant Jupiter in the morning sky. Then in the evening sky on October 27 and 28 a waxing crescent will dance above the Teapot right in the Milky Way and Mars will join it. Whew! Real lunacy this month! 😉

But I’m keeping my fingers crossed about the weather for the total lunar eclipse. This is one of four in a two-year period with others due next spring and fall. The first in this series –  last spring – was clouded out for me and I at first thought this one would be uninteresting, coming as it does, right near sunrise for my location. But that’s actually going to make it all the more interesting – especially from a photographic perspective! Here’s why.

Totality actually starts at 6:25 am EDT, 23 minutes before sunrise. Now I figure 5-10 minutes after totality begins the Earth’s shadow and the Belt of Venus should be visible in the west as they are about 15 minutes before every sunrise. But this time the Moon itself will be in that shadow.

How cool that will be! But, I’m holding my excitement because it could also be all but invisible!

It would be cool because during the typical total eclipse the Moon is in a dark sky and we can’t see the Earth’s shadow – we just know it must be there because the Moon is getting darker on one side as it moves into  it.  But this time we will have a totally eclipsed Moon sitting right inside the Earth’s shadow which we will see – weather permitting – the entire length of the western horizon.

Now I have no doubt that we will see the Earth shadow – we see it every clear morning – but will we even be able to see the Moon at that point? When totality starts the Moon will be only 4 degrees above the horizon. It sets – locally – about five minutes after sunrise. We can, of course, see even a crescent moon in broad daylight – but this is an eclipsed Moon.

So will it be visible at all and how visible? Even during the partial phases I expect it to be a little hard to pick up in a brightening sky. The partial eclipse begins at 05:15 am EDT. Astronomical Twilight – the first detectable lightening of the sky – starts a couple minutes later.

So during the partial phases we’ll have a moon that’s getting darker and darker and a sky that’s getting progressively lighter. Not much contrast. Civil Twilight begins at 06:21 for me with the moon is a tad less than five degrees above the horizon and close to totally eclipsed.

But now the question becomes how clear is the western horizon? The slightest bit of cloudiness will show up and obscure the moon when it’s at that altitude.

So the bottom line is this: I have no doubt that I will see the early stages of a partial eclipse. I simply don’t know at what point – even given perfect weather – it will start to become difficult to see and lose it’s appeal as two things work against visibility – the lightening sky and the Moon drawing closer to the horizon.

This, of course, will make it a challenging photographic target – but then remember, the camera can see things that are a bit fainter than what our naked eye sees – even with an exposure of just a second or two. Tripod needed, of course, and remote shutter release handy. But wait – we will be so close to dawn we can’t use a real slow shutter speed or it will wash everything else out. And that’s where I’m thankful for digital cameras because they’ll let us take test shots and check the results, immediately, over and over!

It’s probably a pipe dream,  but I would really like to see – and photograph – a beautiful shadow of the Earth topped by a deep red Belt of Venus with a barely detectable full Moon sitting on the horizon in the middle of the Earth’s shadow. Last year I got the full moon rising with the Earth’s shadow as a backdrop – that was neat, but of course the Moon wasn’t actually in the shadow at that point and it was at its  brightest.

Technically possible, I guess – so I’m skeptical, but please – surprise me!

In any event, here’s the complete relevant time table. The  lunar eclipse times are constant for any location, though of course you will have to convert them form EDT if you’re in a different zone. Sunrise and twilight times are strictly local. They apply to my location in southeastern Massachusetts and should be checked locally. To find them I use the service provided  by the Naval Observatory and found here.

For detailed advice on photographing a lunar eclipse go here.

Here’s my local time table – I’m at 71° 04′ W and 41° 33′ N

Lunar eclipse timetable – EDT  –  Plus Moon’s altitude

05:15 Partial eclipse begins 16.5°

05:17 Astronomical Twilight Begins     16.5°

05:49 NauticalTwilight Begins     10.4°

06:21 Civil Twilight begins 4.7°

06:25 Total eclipse begins 4°

06:48 Sun rise on horizon

06:53 Moon set

October’s Partial Solar Eclipse

From a photographic stand point I find a partial solar eclipse far, far, far less exciting than a total solar eclipse and more dangerous. You simply need to know that you shouldn’t be looking at the sun, even partially eclipsed, without special protection for you and your camera.

But if you’re in a section of North America where the partial eclipse will be good, I suggest you check out this site to find exact times for your locality – http://www.timeanddate.com/eclipse/solar/2014-october-23 

 – and then go here for observing and photographing information.

http://www.eclipse-chasers.com/photo/Photo18.html

Because the Moon’s shadow seeps across the Earth during a solar eclipse, the time they occur depends on your location. With the lunar eclipse they happen at the same Universal Time everywhere as the Moon moves into the Earth’s shadow – but, of course that time has to be adjusted for time zones.

Other Special Night Sky Photo Ops in October

My goal, as always, is to include that most beautiful – and interesting – of planets, Earth, in any of my astronomical photography. To that end the idea is to look at when planets and the Moon approach closely and plan in advance what you wish to include in your Earth-sky photographs.

You don’t need a special event – or even the Moon – for this sort of thing, of course. I was photographing Saturn, Mars, and Antares with a crescent Moon low in the west over a seacoast last month. I was happy with this result.

September 27,2014 - c. 45 minutes after sunset looking west on beach in front of Allens Pond. Dartmouth, MA.  Waxing Moon with Saturn just south - plus Mars and Antares. (Click image for larger version.)

September 27,2014, an hour after sunset looking west on beach in front of Allens Pond. Dartmouth, MA. Waxing Moon with Saturn just south of it – plus Mars and Antares. (Click image for larger version.)

But I was happier when I turned around and caught the outlines of some folks sitting on a nearby large rock, as well as the glow of distance city lights to the north and the rising stars in the general area of Perseus and Triangulum. (Both these images need to be clicked on and displayed  large to see details.)

September 27,2014 - 90 minutes after sunset looking east on beach in front of Allens Pond. Dartmouth, MA.

September 27,2014 – 90 minutes after sunset looking east on beach in front of Allens Pond. Dartmouth, MA. (Click image for larger version.)

So here are the situations I would anticipate as offering some special opportunities this month.

Jupiter is quite high in the Eastern morning sky and very bright, so just about any time this month it offers a good twilight opportunity with the stars of nearby Leo. With it this high, however, you’ll probably want to be closer to foreground objects – trees, buildings, boats – whatever  – to include them.

A couple hours before sunrise you’ll find Jupiter roughly 45 degrees (4-5 fists) in the eastsoutheast and unmistakeable as the brightest “star” in the sky.

On the mornings of October 17 and 18 it will be joined by a waning crescent Moon less than 10 degrees – one fist – away – a nice combination. To take advantage of this you want to scout out locations that would offer a nice, twilight scene to the southeast.

The evening sky will offer a simlar situation, but with a waxing crescent Moon and the center of our Milky Way as background. Mars will be in the vicinity, but the distinctive “Teapot”  asterism which highlights Sagittarius will make it especially interesting. Will the Moon totally drown out the Milky Way? Certainly it will impact some of it, but this will be an interesting night sky challenge

Starting on the evening of October 26 a waxing crescent about three days old will form a rough triangle with Saturn and Antares low in the south-southwest. Antares and Saturn may be too low to see depending on how clear your horizon is.  The Moon you won’t miss.

In the next two days the Moon climbs higher and moves in the general direction of Mars, the Teapot, and the Milky Way. I think this provides an interesting combination through the 28th, but with each successive day the moon gets brighter and brighter, and thus will drown out more and more of the Milky Way in it’s area.  So I think the best opportunity will be on the 26th – but you can only be sure by getting out and seeing – and snapping.

Look North in October 2013 – and find a really bright star!


Click image for larger view. (Prepared from Starry Nights Pro screen shot.)

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

When I say “really bright,” I mean Capella – and I say it because so many folks assume, quite understandably, that the North Star will be the brightest in that section of the sky. It isn’t.

Capella is one of our brightest stars, and you may catch it this month just peeping up over the northeastern horizon about an hour and a half after sunset. And it is brilliant!  When you see Capella,  compare it with the North Star  and you will get a good idea of what the word magnitude means. There are a solid two magnitudes difference between the two – or if you want to get technical, Capella is magnitude 0 and Polaris is magnitude 2.

Yes, the magnitude system goes backwards – the lower the number, the brighter the star. Each magnitude difference represents a change of about 2.5 times in brightness. So a zero magnitude star is 2.5 times as bright as a first magnitude star – and 2.5 x 2.5, or 6.25 times as bright as Polaris, a second magnitude star. And while we’re on this subject, the faintest star in the Little Dipper – it’s over in one corner of the cup – is just about magnitude five. That means Capella is 100 times as bright as that star. (OK – if you actually do the math it doesn’t come out because I rounded off the difference – it’s really 2.512 for those wanting more precision.)

In fact, there is another interesting way to look at that star – at magnitude 4.9 it is almost exactly what our Sun would look like if it were placed just 32.5 light years away. At that distance our sun would be magnitude 4.8 – and that distance is the distance we use to compare stars. That is, to get an “absolute magnitude” for them so we can compare apples with apples,  we ask ourselves how bright a star would be if it were 32.5 light years from us.

And while we’re on the subject of magnitude, the Little Dipper does give us a great range. Polaris, as we said, is magnitude 2. The other bright star in the Little Dipper is magnitude 2 also – it’s at the end of the cup away from Polaris. Sharing that end is a magnitude 3 star, and these two are known as the “Guardians of the Pole” as they are prominent, close, and like other stars, circle around the pole  every 24 hours. Most of the other stars in the Little Dipper are magnitude 4, with the one star in the corner of the cup being magnitude 5, as noted – well, actually 4.9. There’s a chart with these magnitudes in this post. Many people who live in light-polluted areas can see only three stars in the Little Dipper – Polaris and the two Guardians of the Pole.

How faint a star can you see? Depends upon your eye sight, the light pollution in your area, the transparency of the skies on any given night, how high the star is in the sky, and, of course, your vision and dark adaption. But as a general rule of thumb magnitude 6 has been accepted as the typical naked eye limit. However, if you live in a typically light polluted suburb you may see only to 4, or worse yet, magnitude 3. And observers on mountain tops with really clear skies reliably report seeing stars as faint as magnitude 8. All of this is with the naked eye. Add ordinary binoculars and you will certainly add three to five magnitudes to the faintest star you can see. In fact, you take a huge jump in the number of stars seen just by using binoculars with 50mm objective lenses. That’s why many amateur astronomers with fine telescopes also are likely to have a pair of 10X50 binoculars that they keep handy. I always did, but more recently I stumbled upon some very inexpensive Celestron 15X70 binoculars that I love for quick peaks, though they are two powerful and large to hold steady for serious observing.

Capella will be a “look east” guide star next month, but you can get to know it this month as you look north. And if you live in mid-northern latitudes, it will become a most familiar site. In fact, where I live – about latitude 42°N – it is in the night sky at some time every night of the year. This is because it is so far north that as it circles Polaris, it only dips below the horizon for a few hours at a time.

Venus gives the Little King a morning kiss!

Looks eats in the morning sky of October 3, 2012. Click image for larger version – prepared from Starry Nights Pro screen shot.

Exactly how this event looks to you really depends on where you are. From my observation point on the Eastern Seaboard, I’ll catch Venus and Regulus very close to their closest approach with a separation of about 8 minutes of arc shortly after 4 am on October 3, 2012.  By the time the pair rises for West Coast viewers. the separation will be closer to 12 minutes. And, of course, those in “Down East” Maine will have a slightly better view of the event than I do.

But for all of North America and for some other places as well, it will be fun – weather permitting – to see Venus at magnitude -4.1 come so close to a first magnitude star, Regulus, at magnitude 1.34. That means Venus will be about 100 times as bright as Regulus, and I’m pretty sure this will make it impossible to see the star with your naked eye, though it should make a real cool view for binoculars and small telescope users. Regulus (Latin for “little king” or “prince.”) gets these close calls because it is so close to the ecliptic – the green line in our chart – which is the general area of the sky where the planets are found. On July 8, 1959, Regulus was occulted by Venus – that is, completely covered.  That will happen again on October 1, 2044. Of course the two aren’t really close. Venus is in our solar system and at this time about eight light minutes from us, whereas Regulus is 78 light years away.

How does this compare with the view of what is probably the best known double star, Mizar and Alcor in the handle of the Big Dipper?  Many people can split this pair with their naked eye, but they are  11.6 minutes apart.  So just considering the separation in minutes of arc, Venus and Regulus should be very, very difficult to split with  the naked eye. But Mizar and Alcor are  less than two magnitudes apart – a difference of about 6 times in brightness – and that makes it much easier to split them.

Still – I plan to watch starting about 4 am EDT when the pair are high enough above the horizon to see easily. As sunrise nears, the gap will widen to 10 or 11 minutes and separating them may get a bit easier as the glare of Venus will be diminished against the pre-dawn glow. If nothing else, this will certainly drive home the message of how quickly Venus is moving. By the next morning they are separated by more than a degree – still nice to see – and by October 8th or 9th you’ll be hard pressed to fit them both in the same binocular field of view!

Look east in October 2012 – see a bow, the demon star, and a distant galaxy

On tap this month are:


To begin our monthly exploration of the night sky in the east, you can take a slide down Andromeda’s Couch to Mirfak and the Bow of Perseus in the northeast – that is, you can if you learned how to find Andromeda’s Couch last month. If that’s new to you, ignore it for now and simply start by looking for the “Bow” of three bright stars rising low in the northeast.

To find it, go out about an hour after sunset and watch the bright stars emerge. It may take a few minutes to see the bow clearly, but what you are looking for is three stars in a vertical arc, with the middle one – Mirfak – the brightest. How big an arc are we talking about? Just make a fist and hold it vertically at arm’s length, and your fist should just cover these three stars. How high? The bottom one should be about a fist above the horizon. Here’s a chart modified from Starry Nights Pro software.

Click image for larger version. (Derived from Starry Nights Pro screen shot.)

For a printer friendly version of this chart, go here.

The bow asterism is the core of the constellation Perseus. Now if you want to be a stickler about mythology, Perseus doesn’t carry a bow – he wields a sword instead, which he is holding in his right hand high over his head, while in the left hand he holds the severed head of Medusa. Here’s how the 1822 “Urania’s Mirror” depicted him.

perseus
Perseus – click for a larger version.

Oh boy – and if you can see all that in these stars, then you have a very vivid imagination. I never would have learned the night sky if I had to try to trace out these complex constellations as imagined by ancient cultures and depicted in star guides up until fairly recently. And for the purposes of helping you find your way around the night sky I think remembering the “Bow of Perseus” is easier.

Getting sharp about brightness

As you start to learn the stars, it may surprise you how precise you can be about their brightness. At first you may have difficulty just telling a first magnitude star from a second, but if you get to know Algol, the “Demon Star,” I bet you’ll find that you can quickly become quite sophisticated in assessing brightness and shaving your estimates down to as little as a tenth of a magnitude. So let’s take a closer look at the Bow and three bright stars in this region – Mirfak, Algol, and Almach.

Imagine a star that regularly varies in brightness every few days – that’s what Algol does. Exactly every 2 days, 20 hours, and 49 minutes it begins a 10-hour period where its brightness dims more than a full magnitude. If you look during the right two hours, you’ll catch it at or near its dimmest – and most of the rest of the time you’ll catch it at or near peak brightness. And it’s quite easy to judge. But first let’s find it. Here’s the chart we’ll use.

Notice how Algol makes a very nice triangle with two companions, and all three stars are close to the same brightness – Almach, the northern-most star in Andromeda’s Couch; Mirfak, the central star in the Bow of Perseus; and Algol. Algol is called the “Demon Star” because it varies in brightness – and, of course, it marks the head of Medusa. Gazing directly at her turned onlookers to stone according to Greek mythology – but I hope that doesn’t worry you because I’m going to ask you to stare directly at her – or at least at Algol! In fact, that relates to our first challenge: Go out any clear night and study these three stars and decide which is the brightest. Two are equal in brightness, but one is a tad brighter than the other two. Which is it? Algol? Mirfak? Almach? (The answer is at the end of this post so you can ignore that answer until you actually have an opportunity to test yourself.)

However . . .

Because Algol is a variable, sometimes when you look at it, Algol will actually be significantly dimmer than either Mirfak or Almach. In fact, there’s a reasonable chance it will be dimmer than either of Mirfak’s two fainter companions that make up the Bow of Perseus. If, when you test yourself, this is the case, congratulations! Make note of the date and time. But that’s not the test – just fun! For the test you want the “normal” condition, which has these three nearly the same in brightness.

OK? Back to Algol. It’s a special kind of variable star known as an eclipsing binary. That is, what looks like one star to us is really two stars very close together, and when we see Algol’s light start to dim it means its companion is passing between Algol and us causing an eclipse. Since the stars are locked in orbit around one another this happens with clockwork regularity.

algol_edu

The above diagram came from this astronomy class web site which includes a more detailed scientific explanation. Since either star of the pair can cause an eclipse, there is a much fainter, secondary eclipse of Algol – really too faint to be noticed by most observers. Why is one eclipse fainter – because one star is blue and much hotter/brighter than the other star. It is when the cooler star is in front that we see the dramatic change in light.

It’s fun to catch Algol in mid eclipse, but I suggest you not read about when to do this right now. Instead, do the little challenge first. Then when you’re ready, go to the final item in this post, which explains how and when to catch Algol in eclipse and in the process, tells you the brightness of its companions.

See a few hundred billion stars at one glance!

Yes, you can do it if you have good dark skies, you have allowed your eyes to dark adapt, and you are looking at the right place. Once again, Andromeda’s Couch is our guide, and what we are looking for this time is the Great Andromeda Galaxy aka M31.

This is our “neighbor” in space if you can wrap your mind around the idea that something “just” 2.5 million light years away is a “neighbor.” As you try to do that remind yourself that a single light year is about 6 trillion miles – of course, good luck if you can imagine a trillion of anything! OK – let’s try that – quickly. If you wanted to count one million pennies, and you counted one every second, it would take you 11 days. A billion pennies would take you about 31.7 years! And a trillion pennies? 31,700 years – roughly the time that has elapsed since the earliest cave paintings. So what if you were the cabin boy on an inter-galactic spaceship charged with ticking off the miles at the rate of one mile a second on the way to Andromeda? Think you could do it? Think you would live long enough? Hardly! The task – and journey – would take you almost half a million years – or by my crude estimate 475,650 years! And that’s non-stop counting. Ohhh – are we there yet, Mom?

And yet here you are collecting photons in your backyard that got their start on the journey to your eyes some 2.5 million years ago! Even if you live under normal, light-polluted skies, you should be able to see the Andromeda Galaxy with binoculars. In fact, this is one object where the binocular view can be as rewarding as the view through a telescope. Here’s a wide field chart for mid-month and about 90 minutes after sunset. At that point the galaxy should be roughly half way up your eastern sky. (Look for it on a night when the moon isn’t in the sky and when, of course, your eyes have had at least 15 minutes to dark adapt.)

Click image for larger version.

Starting with the preceding chart – and moving to the chart below, here’s a more detailed star-by-star hop to the Andromeda Galaxy:

  1. Locate the Great Square
  2. Locate Andromeda’s Couch off the northeast corner of the Square.
  3. Go down to the middle star in the couch, then count up two stars and bingo!
  4. You can also find the general vicinity by using the western end of the “W” of Cassiopeia as if it were a huge arrowhead pointing right at the Andromeda Galaxy.

Well, “bingo” if you have been doing this with binoculars. With the naked eye it’s more an “oh yeah – I see it – I think!” But what do you expect? Think about it. The light from the near side of this object started its journey about 150,000 years before the light from the more distant side did! And think of where the human race was 2.5 million years ago when these photons began their journey – or for that matter, where all these stars really are today! Nothing is really standing still – everything is in motion.

You might also want to think about the folks who are on a planet orbiting one of those stars in the Andromeda Galaxy and looking off in our direction. What will they see? A very faint patch – certainly  fainter than what we see when we look at the Andromeda Galaxy, but in a modest  telescope  roughly similar in shape, though about two-thirds the size. Both Andromeda and the Milky Way Galaxy we inhabit are huge conglomerations of stars. We’re about 100,000 light years in diameter – Andromeda is about 150,000 light years in diameter. The Milky Way contains perhaps 100 billion stars – the Andromeda Galaxy maybe 300 billion. (Don’t quibble over the numbers – even the best estimates are just estimates. )

And yes, in a few billion years we will probably “collide” with the Andromeda Galaxy, for we are hurtling towards one another. Such galaxy collisions are not that unusual and probably aren’t as violent as the word “collision” makes them sound – but they do, in slow motion, bring about radical changes in one another.

But all that is for the professional astronomers to concern themselves with – for us, there’s the simple beauty and awe of knowing that with our naked eye – or modest binoculars – we can let the ancient photons from hundreds of billions of stars ping our brains after a journey of millions of years.

So here’s hoping for clear skies for you so you can find a winking demon and capture in your own eye the photons from a few hundred billion stars in the Andromeda Galaxy!

And now the truth about Algol and companions

Have you done the Algol test yet? Looked at Algol, Mirfak, and Almach and tried to decide which is brightest? If so, you can check your answer by continuing to read. If not, I suggest you first do that exercise, then come back to this.

Chances are that when you look at Algol, it will be at its brightest – but how can you tell? Well, as we mentioned, you can compare it to Mirfak – but there’s an even closer match with another nearby bright star – Almach. That’s the third star in Andromeda’s Couch – the one nearest Algol.

Mirfak is the brightest of the three at magnitude 1.8.

Almach is magnitude 2.1 – which is the same brightness of Algol when Algol is at its brightest – which is most of the time. OK – for the hair splitters, Almach is a tad dimmer than Algol, but the difference is far too little to be able to tell with your eye. But that makes Mirfak about one third of a magnitude brighter than the other two. That difference you should be able to see – but it does take practice.

Here’s a chart showing the magnitude of the stars near Algol that you can use to compare it to and see if it is going through an eclipse. People who look at variable stars use charts like this, but with one important exception – the numbers are given like they were whole numbers so you will not confuse a decimal point with another star. Thus, a star like Mirfak, of magnitude 1.8, would have the number “18” next to it. I broke a convention here because there are just a few bright stars on the chart, so I didn’t worry about the possible confusion of a decimal point being mistaken for another star.

So If Algol and Almach are the same, no eclipse is going on at the moment. If Algol appears dimmer than Almach, then an eclipse is in progress. If it’s as dim or dimmer than either of the companions of Mirfak in the Bow, then you can be pretty sure you’ve caught Algol at or near its darkest. In two hours – or less – it will start to brighten and will return to full brightness fairly quickly.

Catching Almach at its dimmest is fun, but not as easy as it may seem. Why? Because although an eclipse happens every few days, it may happen during the daylight hours, or in the early morning, or some other time when it’s inconvenient. And, of course, you need clear skies. So when I want to observe an Algol eclipse, I go to a handy predicting tool on the Web that you can find here.

I then note the dates and times and pick out only those dates when the times are convenient to me – that is, happening during my early evening observing sessions. Then, given the iffiness of the weather, I consider myself lucky when I  get a good look at an eclipse of Algol. What are your chances – given your weather – that it will be clear on a night when an eclipse is visible before your normal bed time?

If I do this for October 2012 I find that out of 12 Algol minima this month, just three hit at the right time for me. Keep in mind the times are for mid-eclipse – it will be this dim an hour before and after the time given. The dates and times best for me are:

  • 10/06/2012 @ 11:32 pm EDT
  • 10/09/2012 @ 08:21 pm EDT
  • 10/29/2012 @ 10:03 pm EDT
  • 11/01/2012 @ 06:51 pm EDT

Of course the dates and time may be different for you, depending on where you live, and none of us can escape the whims of the weather!

Look North in October 2012 – and find a really bright star!


Click image for larger view. (Prepared from Starry Nights Pro screen shot.)

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

When I say “really bright,” I mean Capella – and I say it because so many folks assume, quite understandably, that the North Star will be the brightest in that section of the sky. It isn’t.

Capella is one of our brightest stars, and you may catch it this month just peeping up over the northeastern horizon about an hour and a half after sunset. And it is brilliant!  When you see Capella,  compare it with the North Star  and you will get a good idea of what the word magnitude means. There are a solid two magnitudes difference between the two – or if you want to get technical, Capella is magnitude 0 and Polaris is magnitude 2.

Yes, the magnitude system goes backwards – the lower the number, the brighter the star. Each magnitude difference represents a change of about 2.5 times in brightness. So a zero magnitude star is 2.5 times as bright as a first magnitude star – and 2.5 x 2.5, or 6.25 times as bright as Polaris, a second magnitude star. And while we’re on this subject, the faintest star in the Little Dipper – it’s over in one corner of the cup – is just about magnitude five. That means Capella is 100 times as bright as that star. (OK – if you actually do the math it doesn’t come out because I rounded off the difference – it’s really 2.512 for those wanting more precision.)

In fact, there another interesting way to look at that star – at magnitude 4.9 it is almost exactly what our Sun would look like if it were place just 32.5 light years away. At that distance our sun would be magnitude 4.8 – and that distance is the distance we use to compare stars. That is, to get an absolute magnitude for them so we can compare apples with apples,  we ask ourselves how bright a star would be if it were 32.5 light years from us.

And while we’re on the subject of magnitude, the Little Dipper does give us a great range. Polaris, as we said, is magnitude 2. The other bright star in the Little Dipper is magnitude 2 also – it’s at the end of the cup away from Polaris. Sharing that end is a magnitude 3 star, and these two are known as the “Guardians of the Pole” as they are prominent, close, and like other stars, circle around it every 24 hours. Most of the other stars in the Little Dipper are magnitude 4, with the one star in the corner of the cup being magnitude 5, as noted – well, actually 4.9. There’s a chart with these magnitudes in this post. Many people who live in light-polluted areas can see only three stars in the Little Dipper – Polaris and the two Guardians of the Pole.

How faint a star can you see? Depends upon your eye sight, the light pollution in your area, the transparency of the skies on any given night, how high the star is in the sky, and, of course, your vision and dark adaption. But as a general rule of thumb magnitude 6 has been accepted as the typical naked eye limit. However, if you live in a typically light polluted suburb you may see only to 4, or worse yet, magnitude 3. And observers on mountain tops with really clear skies reliably report seeing stars as faint as magnitude 8. All of this is with the naked eye. Add ordinary binoculars and you will certainly add three to five magnitudes to the faintest star you can see. In fact, you take a huge jump in the number of stars seen just by using binoculars with 50mm objective lenses. That’s why many amateur astronomers with fine telescopes also are likely to have a pair of 10X50 binoculars that they keep handy. I always did, but more recently I stumbled upon some very inexpensive Celestron 15X70 binoculars that I love for quick peaks, though they are two powerful and large to hold steady for serious observing.

Capella will be a “look east” guide star next month, but you can get to know it this month as you look north. And if you live in mid-northern latitudes, it will become a most familiar site. In fact, where I live – about latitude 42°N – it is in the night sky at some time every night of the year. This is because it is so far north and as it circles Polaris only dips below the horizon for a few hours at a time.

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