Look north in September 2014 – the king’s on the rise!

Yes, that’s Cepheus, the King – remember that Cassiopeia (the “W” ) is the Queen. Though Cepheus makes a familiar “home plate” asterism, it’s not nearly so memorable as the “W” of Cassiopeia, primarily because its stars are dimmer than those of the “W.” In fact, you might have difficulty picking it out at first, but here’s a tip: Follow the familiar “Pointers” of the Big Dipper to the North Star – then keep going, but not too far. The first bright star you meet will mark the tip of the Cepheus home plate – It’s about one fist away from Polaris. For comparison, the Pointer stars are nearly three times that far in the other direction.

Also coming up below the “W” is the “Bow” asterism that marks Perseus, who is carrying the head of Medusa, which contains the “Demon Star,” Algol. We’ll take that up next month when they’re higher in the sky and easier for all to see. Here’s a chart.

Click image for a larger version. (Developed from Starry Nights Pro screenshot.)

For a printer-friendly version of this chart, download this.

To review the connecting mythology, which helps me remember the related constellations, here’s the story in brief.

Cepheus and Cassiopeia have a daughter Andromeda whose beauty makes the sea nymphs jealous. They enlist Poseidon to send a sea monster to ravage the coastline of Ethiopia, the kingdom of Cepheus and Cassiopeia. To appease the monster, the good king and queen chain Andromeda to a rock along the coast, but Perseus rescues her and together they escape on Pegasus, his flying horse.

You meet Andromeda and Pegasus – the flying horse is much easier to identify as the “Great Square” – in the “Look East” post this month. Also in the “Look East”  post we detail the “Three Guides,” three stars that mark the zero hour in the equatorial coordinate system used to give a permanent address to all stars. The first of those Three Guides is Beta Cassiopeia, visible in our northeastern sky, and so on the chart with this post.

Moving from mythology to science, Cepheus is probably best known today for a special type of star called a Cepheid variable. This is a star that changes in brightness according to a very precise time table. What’s more, it was discovered that the length of a Cepheid’s cycle – that is the amount of time it takes to grow dim and then brighten again – is directly related to its absolute magnitude. The absolute magnitude of a star is a measure of how bright it really is as opposed to how bright it appears to us. (How bright it appears is, of course, related to how far away it is.) That makes Cepheid variables a sort of Rosetta Stone of the skies.

It is relatively easy to time the cycle of a variable, even if the star is quite faint from our viewpoint. These cycles usually cover a few days. If you can identify the length of this cycle, you then can know the absolute magnitude of a star. And if you know its absolute magnitude, it’s a simple matter to compare that to how bright it appears to us and thus determine its approximate distance from us.

This is a huge breakthrough. Without Cepheid variables astronomers were at a loss for determining the distance of anything that was more than a few hundred light years away. The distance to such “close” stars could be determined using a very common method known as parallax – that is, determining how the star appeared to change position slightly from opposite sides of the Earth’s orbit. But that change in position is extremely tiny and difficult to measure even with very close stars. With the Hipparcos satellite and computer analysis, it has been possible to use this parallax system for stars as far as 3,000 light years. But that still is close by astronomy standards. (Keep in mind our galaxy is about 100,000 light years across.) But Cepheid variables can even be found in other galaxies. In fact, they played a huge role in proving that “spiral nebulae” were really other “island universes” – that is, other galaxies. The Hubble Space Telescope has found Cepheids out to a distance of about 100 million light years – a huge leap from the 3,000 light years we can reach with the parallax method.

There are other ways of making an educated guess at an object’s distance, and they frequently are quite complex and indirect. But the Cepheid variable has been one of the most important tools in the astronomer’s tool kit for the past century. It was in 1908 that Henrietta Swan Leavitt, a $10.50 a week “calculator” at Harvard Observatory noticed a pattern while doing tedious work cataloging stars and saw it’s importance. Though she published a paper about it, she never really received the credit she deserved during her lifetime for this breakthrough discovery.

So when you look at this “home plate” in the sky, see if you can find the fourth magnitude star, Delta Cephei – it’s not hard to spot under good conditions. (See the chart above.) When you find it, pay homage to it for the key role it has played in unlocking the secrets of the universe – for once astronomers know the distance of an object they can make all sorts of deductions about its composition, mass, and movement.

Look east In September 2013 – and take a journey from mythology to science

As we travel September skies we’ll move from the age of mythology to the age of science.

First, the age of mythology. Had you been born a few hundred – or even a few thousand – years ago, the eastern sky in September shortly after sunset would look something like this to your imaginative eye.

For most of recorded human history different cultures turned the stars into familiar patterns that illustrated familiar mythological stories. In our September eastern skies shortly after sunset we have a wonderful collection of five related mythological figures – Cepheus  (king), Cassiopeia  (queen), Andromeda  (princess), Perseus  (hero), and Pegasus, the flying horse. (Slightly modified screen shot of Starry Night Pro. Click for larger version.)

The tale is easy to remember. The king (Cepheus) and queen (Cassiopeia) felt their kingdom was threatened by a sea monster, so as a sacrifice to the monster they tied their daughter, Andromeda, to a coastal rock. m But don’t worry, our hero Perseus, fresh from slaying Medusa, appears to rescue Andromeda, and they ride off across the starry heavens on his faithful steed, Pegasus, the flying horse.  Really – today the king and queen  would be tried for child abuse!

Of course as usual with the ancient constellations, the figures bear only the crudest relationship to the pattern of bright stars, so a lot of imagination is required to see them.  But that said, I do find this myth an easy way to remember these five constellations. In modern times we’ve drawn complex boundaries around each constellation and used these imaginary celestial boundaries to name and locate stars.  But more importantly, we’ve developed a celestial coordinates system much along the lines of Earthly longitude and latitude.

If you imagine the Earth’s latitude lines projected onto the dome of the sky, they become circles indicating declination – how far in degrees a point is from the celestial equator. The celestial equator itself is a projection onto the sky dome of Earth’s equator.  Longitude is projected and marked in 24 hours of “right ascension” so the whole celestial clock appears to pass overhead in the course of a day. I found it difficult remembering where these hours begin until I learned about the “Three Guides.” These are three bright stars –  indicated by arrows in the chart below – that fall very close to the zero hour line of right ascension. Above them (think of these as preceding them, for they rise first)  the hours count backward from 24. Below them – think of these  as following them, since they rise afterwards – are the hours counting up from 0.

I prefer to remember my sky in terms of bright stars and asterisms, so Cassiopeia becomes the “W.” Andromeda  becomes “Andromeda’s Couch,”  and the flying horse becomes the “Great Square.”   But the Three Guides – the three bright stars indicated by arrows – allow you to see the sky in more scientific terms, for these are the starting points for laying a grid on the sky to create a precise address for each star in terms of its places on the grid. This grid is indicated above by the red lines. (Prepared from a Starry Nights Pro screen shot – click for a larger version.)

For a printer-friendly version of this chart, download this.

First, let’s look at the “Great Square” – or perhaps we should say “Great Diamond,” since that’s what it looks like when rising. Once overhead, it is certainly a square, and it forms the heart of Pegasus – the flying horse. The stars are all second and third magnitude – about the brightness of the stars in the Big Dipper – so wait until about an hour after sunset, then look east and you should be able to pick this out. Its stars mark out a huge chunk of sky that is nearly empty of naked-eye stars, which is why I sometimes call it the “Great Empty Square.”

Andromeda’s Couch, ties to the northern corner of the square. In fact, it shares a star with this corner. “Andromeda’s Couch” is just my memory device – others would simply call this “Andromeda” because that’s the name of the constellation it dominates. I have difficulty seeing the lovely maiden chained to a rock by looking at these stars.  But knowing that in myth Andromeda was a lovely woman who was rescued by Perseus, I like to think of this graceful arc of stars as her couch with her a misty fantasy figure lying there in alluring fashion. That said, notice three things about it:

1. The bright star at the right – southern – end is also a corner of the Great Square, as we mentioned. In fact, it is the brightest star in the Great Square.

2. The three brightest stars in the “couch” – I’m ignoring the second star which is fainter – the three brightest are about as close to being identical in brightness as you can get – magnitude 2.06, 2.06, and 2.09. They also are pretty equally spaced. Hold your fist at arm’s length and it should easily fit in the gaps between these stars, which means there are 10-15 degrees between each star. That’s similar to the spacing between the four stars in the “Great Square” as well.

3. The second star, as mentioned, is dimmer by more than a full magnitude (3.25), but it’s what gives this asterism a couch feeling to me – or maybe a lounge chair – marking a sharp, upward bend.

And where’s the hero Perseus? he should be nearby, right? Well he’s on his way, rising in the northeast after Cassiopeia, but we’ll leave him for next month when he’s more easily seen.

Now for the pièce de résistance!

This is a group of stars that are new to me, at least in this role, and I love them! They’re called “The Three Guides,” but I think of it as four guides They can all be tied together by a long, graceful arc that represents the great circle of zero hour right ascension – which is the “celetsial meridian” as defined in the equatorial coordinate system.

As mentioned, the equatorial coordinate system is essentially a projection of the Earth’s latitude and longitude system onto the sky to enable us to give a very precise address for any star or other celestial object, as seen from our planet. On Earth we require an arbitrary circle be chosen as the zero longitude line, and this is the circle that passes through the poles and Greenwich, England.

In the heavens we also need such a circle, and the one chosen is the one that passes through the point where the Sun crosses the celestial equator at the vernal equinox. But that point is not represented by any bright star, so how do we know where this “zero hour” circle is? We need it to put numbers to the entire system. Enter “The Three Guides.”

They start with the star Beta Cassiopeia. This is the western most star in the familiar “W”  – the one which rises first and leads the rest. (Remember – all stars appear to move westward as the earth turns.)  From there draw an arc to Alpha Andromedae. This is the star mentioned before where Andromeda and the Great Square are joined – they both share this star.

The third star of this trio is Gamma Pegasi – the star that appears to be at the bottom of the Great Square when we see it as a diamond when rising. (If this is not clear, one glance at the accompanying chart should make it so.)

When I look at this great arc, however, I always start to trace it right from the North Star, Polaris. All the great circles representing meridians of right ascension pass through the north and south celestial poles.

As you move upward from this zero line in the general direction of the Summer triangle, the hours count backwards counting the Zero Hour as 24. Move downward, towards the horizon and the hours count forward from zero. This sequence is marked on our chart around Polaris.

Taking a wide view of the “Three Guides” to incorporate the North Star and Summer Triangle as well. Here’s what we should see about an hour after sunset. Click image for larger version. (Derived from Starry Nights Pro screen shot.)

For a printer-friendly version of this chart, download this.

What’s important is to be able to visualize this one circle in the sky and connect it with the another circle crossing it at a right angle – the celestial equator. If you can do that, you will have identified the two zero points on the equatorial coordinate system and moved your knowledge of finding things in the sky from the mythological arena to the scientific one. That’s why these three “guides” excite me so. When you can look up at the night sky and see not only a dome, but a curved grid projected on it, and on this grid be able to attach meaningful numbers, then you have graduated to sky explorer, first class!

. . . and the rest of the guideposts?

If you’ve located the new September asterisms and identified The Three Guides, then it’s time to check for the more familiar stars and asterisms you might already know, assuming you have been studying the sky month by month. (If this is your first month, you can skip this section.) So here are the guidepost stars and asterisms still visible in our September skies.

• The Summer Triangle is now high overhead, though still favoring the east. Vega, its brightest member, reaches its highest point about an hour after sunset and moves into the western sky. Altair and Deneb are still a bit east, but will cross the meridian within about three hours of sunset.
• The “Teapot,” marking the area of the Milky Way approaching the center of our galaxy, is due south about an hour after sunset. Well into the southwest you’ll find the red star Antares that marks the heart of the Scorpion.
• Arcturus (remember, follow the arc of the Big Dipper’s handle to Arcturus) is due west and about 25 degrees above the horizon as twilight ends.
• The Keystone of Hercules and the circlet that marks the Northern Crown can both be found high in the western sky by tracing a line between Vega and Arcturus.

Look north in September 2013 – the king’s on the rise!

Yes, that’s Cepheus, the King – remember that Cassiopeia (the “W” ) is the Queen. Though Cepheus makes a familiar “home plate” asterism, it’s not nearly so memorable as the “W” of Cassiopeia, primarily because its stars are dimmer than those of the “W.” In fact, you might have difficulty picking it out at first, but here’s a tip: Follow the familiar “Pointers” of the Big Dipper to the North Star – then keep going. The first bright star you meet will mark the tip of the Cepheus home plate. (It’s about one fist away from Polaris – the Pointer stars are nearly three times that far in the other direction.)

Also coming up below the “W” is the “Bow” asterism that marks Perseus, who is carrying the head of Medusa, which contains the “Demon Star,” Algol. We’ll take that up next month when they’re higher in the sky and easier for all to see. Here’s a chart.

Click image for a larger version. (Developed from Starry Nights Pro screenshot.)

For a printer-friendly version of this chart, download this.

To review the connecting mythology, which helps me remember the related constellations, here’s the story in brief.

Cepheus and Cassiopeia have a daughter Andromeda whose beauty makes the sea nymphs jealous. They enlist Poseidon to send a sea monster to ravage the coastline of Ethiopia, the kingdom of Cepheus and Cassiopeia. To appease the monster, the good king and queen chain Andromeda to a rock along the coast, but Perseus rescues her and together they escape on Pegasus, his flying horse.

You meet Andromeda and Pegasus – the flying horse is much easier to identify as the “Great Square” – in the “look east” post this month. Also in the “Look East”  post we detail the “Three Guides,” three stars that mark the zero hour in the equatorial coordinate system used to give a permanent address to all stars. The first of those Three Guides is Beta Cassiopeia, visible in our northeastern sky, and so on the chart with this post.

Moving from mythology to science, Cepheus is probably best known today for a special type of star called a Cepheid variable. This is a star that changes in brightness according to a very precise time table. What’s more, it was discovered that the length of a Cepheid’s cycle – that is the amount of time it takes to grow dim and then brighten again – is directly related to its absolute magnitude. The absolute magnitude of a star is a measure of how bright it really is as opposed to how bright it appears to us. (How bright it appears is, of course, related to how far away it is.) That makes Cepheid variables a sort of Rosetta Stone of the skies.

It is relatively easy to time the cycle of a variable, even if the star is quite faint from our viewpoint. These cycles usually cover a few days. If you can identify the length of this cycle, you then can know the absolute magnitude of a star. And if you know its absolute magnitude, it’s a simple matter to compare that to how bright it appears to us and thus determine its approximate distance from us.

This is a huge breakthrough. Without Cepheid variables astronomers were at a loss for determining the distance of anything that was more than a few hundred light years away. The distance to such “close” stars could be determined using a very common method known as parallax – that is, determining how the star appeared to change position slightly from opposite sides of the Earth’s orbit. But that change in position is extremely tiny and difficult to measure even with very close stars. With the Hipparcos satellite and computer analysis, it has been possible to use this parallax system for stars as far as 3,000 light years. But that still is close by astronomy standards. (Keep in mind our galaxy is about 100,000 light years across.) But Cepheid variables can even be found in other galaxies. In fact, they played a huge role in proving that “spiral nebulae” were really other “island universes” – that is, other galaxies. The Hubble Space Telescope has found Cepheids out to a distance of about 100 million light years – a huge leap from the 3,000 light years we can reach with the parallax method.

There are other ways of making an educated guess at an object’s distance, and they frequently are quite complex and indirect. But the Cepheid variable has been one of the most important tools in the astronomer’s tool kit for the past century. It was in 1908 that Henrietta Swan Leavitt, a $10.50 a week “calculator” at Harvard Observatory noticed a pattern while doing tedious work cataloging stars and saw it’s importance. Though she published a paper about it, she never really received the credit she deserved during her lifetime for this breakthrough discovery.

So when you look at this “home plate” in the sky, see if you can find the fourth magnitude star, Delta Cephei – it’s not hard to spot under good conditions. (See the chart above.) When you find it, pay homage to it for the key role it has played in unlocking the secrets of the universe – for once astronomers know the distance of an object they can make all sorts of deductions about its composition, mass, and movement.

Look east in October 2011 – see a bow, the demon star, and a distant galaxy – plus Jupiter

On tap this month are:

• a new asterism, the bow
• Jupiter, pops onto the eastern horizon and it is bright!
• a variable star, Algol, aka the “demon star”
• a neighboring galaxy you can see with the naked eye or binoculars

To begin our monthly exploration of the night sky, 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 it.

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.

Jupiter pops onto the eastern horizon and it is bright!

You may not see the King of Planets just an hour after sunset – and certainly won’t unless you have a clear eastern horizon – but be patient. It will be there.  Jupiter is reasonably high about two hours after sunset the first of the month and by the 15th it is just peeping above the horizon – about   3 degrees high  –  just an hour after sunset. You can see it on our “look east” chart above.  Since it rises about four minutes earlier each night it will be well up ( 12 degrees – more than a fist above the horizon)  by an hour after sunset at the end of the month.

The fun of Jupiter is it’s four Galilean moons – one or more of which can usually be seen with binoculars held real steady – and certainly are visible in any small telescope. (When he discovered them in 1610 Galileo had a poor and tiny telescope compared to the smallest and cheapest available today. ) The moons always line up roughly with Jupiter’s equator, but they change position continuously, some of the changes being noticeable in about an hour. To learn which moon is which and where they are at any given date and hour, go here and click on the special javascript utility. The moons are easier to see as Jupiter gets higher in the sky, so it is good to wait a few hours before trying to see them.  (Plug different times into this script to see how their positions change.)

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.

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 – probably fainter than what we see when we look at the Andromeda Galaxy, but in binoculars and telescopes roughly similar in size and shape. 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.

That bright star rising isn’t a star at all, but the king of planets,  Jupiter!

So here’s hoping for clear skies for you so you can find a winking demon, follow the dance of Jupiter and Urnaus, 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 – the exact 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, 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 usually find that there are only one or two times a month when I’ll get a good look at an eclipse of Algol.

If I do this for October 2011 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:

• 10/05/2011 @ 11:00 pm EDT
• 10/08/2011 @ 07:49 pm EDT
• 10/28/2011 @ 09:30 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 September 2011 – the king’s on the rise!

Yes, that’s Cepheus, the King – remember that Cassiopeia (the “W” ) is the Queen. Though Cepheus makes a familiar “home plate” asterism, it’s not nearly so memorable as the “W” of Cassiopeia, primarily because its stars are dimmer than those of the “W.” In fact, you might have difficulty picking it out at first, but here’s a tip: Follow the familiar “Pointers” of the Big Dipper to the North Star – then keep going. The first bright star you meet will mark the tip of the Cepheus home plate. (It’s about one fist away from Polaris – the Pointer stars are nearly three times that far in the other direction.)

Also coming up below the “W” is the “Bow” asterism that marks Perseus, who is carrying the head of Medusa, which contains the “Demon Star,” Algol. We’ll take that up next month when they’re higher in the sky and easier for all to see. Here’s a chart.

Click image for a larger version. (Developed from Starry Nights Pro screenshot.)

For a printer-friendly version of this chart, download this.

To review the connecting mythology, which helps me remember the related constellations, here’s the story in brief.

Cepheus and Cassiopeia have a daughter Andromeda whose beauty makes the sea nymphs jealous. They enlist Poseidon to send a sea monster to ravage the coastline of Ethiopia, the kingdom of Cepheus and Cassiopeia. To appease the monster, the good king and queen chain Andromeda to a rock along the coast, but Perseus rescues her and together they escape on Pegasus, his flying horse.

You meet Andromeda and Pegasus – the flying horse is much easier to identify as the “Great Square” – in the “look east” post this month. Also in that post we detail the “Three Guides,” three stars that mark the zero hour in the equatorial coordinate system used to give a permanent address to all stars. The first of those Three Guides is Beta Cassiopeia, visible in our northeastern sky, and so on the chart with this post.

Moving from mythology to science, Cepheus is probably best known today for a special type of star called a Cepheid variable. This is a star that changes in brightness according to a very precise time table. What’s more, it was discovered that the length of a Cepheid’s cycle – that is the amount of time it takes to grow dim and then brighten again – is directly related to its absolute magnitude. The absolute magnitude of a star is a measure of how bright it really is as opposed to how bright it appears to us. How bright it appears is, of course, related to how far away it is. That makes Cepheid variables a sort of Rosetta Stone of the skies.

It is relatively easy to time the cycle of a variable, even if the star is quite faint from our viewpoint. These cycles usually cover a few days. If you can identify the length of this cycle, you then can know the absolute magnitude of a star. And if you know its absolute magnitude, it’s a simple matter to compare that to how bright it appears to us and thus determine its distance from us.

This is a huge breakthrough. Without Cepheid variables astronomers were at a loss for determining the distance of anything more than a few hundred light years away. The distance to such”close” stars could be determined using a very common method known as parallax – that is, determining how the star appeared to change position slightly from opposite sides of the Earth’s orbit. But that change in position is extremely tiny and difficult to measure even with very close stars. With the Hipparcos satellite and computer analysis, it has been possible to use this system for stars as far as 3,000 light years. But that still is close by astronomy standards. (Keep in mind our galaxy is about 100,000 light years across.) But Cepheid variables can even be found in other galaxies. In fact, they played a huge role in proving that “spiral nebulae” were really other “island universes” – that is, other galaxies. The Hubble Space Telescope has found Cepheids out to a distance of about 100 million light years – a huge leap from the 3,000 light years we can reach with the parallax method.

There are other ways of making an educated guess at an object’s distance, and they frequently are quite complex and indirect. But the Cepheid variable has been one of the most important tools in the astronomer’s tool kit for the past century. It was in 1908 that Henrietta Swan Leavitt, a $10.50 a week “calculator” at Harvard Observatory noticed a pattern while doing tedious work cataloging stars and saw it’s importance. Though she published a paper about it, she never really received the credit she deserved during her lifetime for this breakthrough discovery.

So when you look at this “home plate” in the sky, see if you can find the fourth magnitude star, Delta Cephei – it’s not hard to spot under good conditions. (See the chart above.) When you find it, pay homage to it for the key role it has played in unlocking the secrets of the universe – for once astronomers know the distance of an object they can make all sorts of deductions about its composition, mass, and movement.

Prime Time observing for September 2009 – a square, a couch, dancing moons, and more!

Please note: All charts with this post are for observers in mid-nothern latitudes centered on 40° N. If you are 10 or more degrees south or north of that – or if you’re not sure of your latitude – please go here to make your own custom star charts.

Our focus as always is the eastern sky, 45 minutes after sunset, where in September 2009 we’ll find a brilliant Jupiter whose moons play a fascinating game of hide and seek. But our main goal will be to locate and remember  this month’s  two new asterisms the Great (empty) Square and Andromeda’s Couch.

Let’s start with Jupiter, though, because no prime time observer can fail to find Jupiter in the eastern sky starting about half an hour after sunset – there’s simply nothing brighter except the Sun and Moon – well nothing brighter in the eastern early evening sky.  Venus gets brighter than Jupiter, but it never appears in the eastern sky after sunset, though it is in the eastern sky these September mornings an hour or so before sunrise. If you’re one who likes to be up then, be sure to take a look – you can’t miss it!

Though not visible to the naked eye, what’s most fascinating about Jupiter is its four brightest moons. Yes, they look a lot like little stars, even in the telescope, but they are in a rough line with the planet’s mid-section and they continuously change positions around the planet from night to night. In fact these changes can be seen over the course of an hour or so, though at the least you need good binoculars that are held very steady in order to see them. Any small telescope, however, should reveal them easily. For an introduction to observing these four moons see the video and text here. This describes moon events for an extraordinary evening – September 2/3, 2009 – but at some time on many evenings you can observe one or two such events, so even if you miss the events of September 2/3, watching the animation and reading this should help you understand similar events that happen quite often whenever Jupiter is visible.

Of course Jupiter is not going to help you learn the rest of the night sky because like all planets it is constantly changing its position relative to the background stars. But our two bright asterisms for September will help and they are as simple as they come – a square with an arc of three bright stars attached to it.

Click chart for a much larger version.

The first is known as the “Great Square.” I call it the “Great (empty)  Square” because the area inside it is almost completely empty of other naked-eye stars.  The other asterism ties to it like the tail of a kite flying sideways.  It streams off one corner and I think of it as “Andromeda’s Couch.” Of course this is just my memory device – others would simply call this “Andromeda” because that’s the name of the constellation it dominates. I have difficulty seeing the lovely maiden, chained to a rock by looking at these stars and their companions, however. Like most constellations, with Andromeda you need a huge imagination to see the figure these stars represented to the ancients. But knowing Andromeda was a lovely woman who was rescued by Perseus, I like to think of this graceful arc of stars as her couch.  That said, notice three things about it:

1. The bright star at the right – southern – end is also a corner of the Great Square. In fact, it is the brightest star of the four that make up the square, but only by a little.

2. The three stars are pretty equally spaced. Hold your fist at arms length and it should easily fit in the gap between the stars which means there are 10-15 degrees between each star. That’s similar to the spacing between stars inthe Square.

3. There’s another dimmer, but fairly bright star, between the first star ( the one at the corner of the Square)  and the middle one.

And where’s the hero Perseus? he should be nearby, right? Well he’s on his way, rising in the northeast after Cassiopeia, but we’ll leave him for next month when he’s more easily seen.

Looking north

Meanwhile, for those in the northern hemisphere, the bright stars circling Polaris and always visible are well represented this month with the Big Dipper starting to move towards the horizon in the northwest and the “W” of Cassiopeia starting to take the dominant role in the northeast opposite it.

Click chart for a larger image. Northern skies as seen from about 40° N latitude in mid-September..

Our chart shows the northern celestial pole region about 90 minutes after sunset when skies are about as dark as they get. Will you see all these stars? Depends. First, on how much light pollution there is where you observe. Second, on how well your eyes are dark adapted. You must avoid white light for at least 15 minutes – better still, half an hour – if you wish to see the fainter stars. If you want to test how good your skies and night vision are, look at the Little Dipper. In light-polluted suburbs you will probably see just the three brightest stars. In good rural conditions you should see all seven.  And if you can see them, then this is a good opportunity to try to trace out Draco, one of a handful of constellations whose connect-the-dots pattern actually suggests the mythological figure of a dragon.  I love Draco, but quite honestly, I have to look for it – it doesn’t jump out at me the way the Big Dipper and the “W” do.  And as far as learning the sky – well, you learn the “W,” the Big Dipper and Polaris so you can then find stuff like Draco when you want to find it.

The arrows on the chart indicate the general direction in which the sky appears to move. Stay out an hour and this motion should become obvious to you.

. . . and the rest of the guideposts?

If you’ve located the new September asterisms then it’s time to check for the more familiar ones you might already know, assuming you have been studying the sky month by month.  (If this is your first month, you can skip this section. ) So here are the guidepost stars and asterisms still visible in our September skies.

• The Summer Triangle is now high overhead, though still favoring the east. Vega, its brightest member, reaches its highest point about an hour after sunset and moves into the western sky. Altair and Deneb are still a bit east, but will cross the meridian within about three hours of sunset.
• The “Teapot,” marking the area of the Milky Way approaching the center of our galaxy, is due south about an hour after sunset. Well into the southwest you’ll find the red star Antares that marks the heart of the Scorpion.
• Arcturus (remember, follow the arc of the Big Dipper’s handle to Arcturus) is due west and about 25 degrees above the horizon as twilight ends.
• The Keystone of Hercules and the circlet that marks the Northern Crown can both be found high in the western sky by tracing a line between Vega and Arcturus.

. . . our journey and September’s planets (2009)

In the course of a night you can still get a glimpse at all the planets – technically – but the truth is both Saturn and Mercury are very difficult to see this month, and Pluto is always just a faint speck visible in large amateur telescopes. Jupiter, as we’ve noted, dominates the evening sky in the southeast. Nearby – visible in binoculars or small telescopes – is Neptune. And an hour or so later, if you want to track it down with binoculars, Uranus will make a good test of your star-hopping skills.  In the morning sky both Mars and Venus are prominent, though Venus gets closer to the Sun throughout the month. At the start of the month Venus rises about three hours before the Sun – by the end of the month this is cut to about two hours – but even in twilight it is so bright it’s hard to miss.

Charts to help you find the  planets follow, but first, let’s look at the solar system from the perspective of someone in a spaceship hovering above it. This shows us where we are in our journey around the Sun and also gives us a chance to examine where the other planets are in relation to us. See if you can translate this perspective into what we see in our sky. The chart below was created with the Solar System Live capability found here. I added the arrows in Photoshop Elements simply to indicate the horizon and directions relating to the earth’s rotation on its axis.

Click image for larger view. Arrows indicate the western and eastern horizons at sunset on September 15, 2009. Smaller arrows show the direction these horizons move as the earth turns on its axis in the course of the night. (Planets are not drawn to scale.)

Looking at the horizon line going out to the west – left – you can see that at sunset Saturn is nearly on the horizon.  Use the arrow going to the east (right) and you can see Uranus isn’t quite visible in our night sky at sunset, but Jupiter, Neptune, and Pluto are well beyond the eastern horizon.  Draw an imaginary line from Earth through Jupiter and you’ll see it comes near Neptune – which is why Neptune appears relatively close to Jupiter in our night sky this month, though you’ll need binoculars to find it. (Notice also that Neptune, while a giant planet, is more than twice the distance from the Sun as Jupiter – which is why it is so dim and small in our night sky while Jupiter is bright – and in a telescope – quite large. As these horizon lines rotate,  Saturn sets, followed by Mercury and  then several hours later Pluto and eventually Jupiter. Meanwhile, Uranus rises in the east, followed in the morning hours by Mars and Venus.  Notice also that Pluto is just a tad beyond Neptune these days, though the distance between them will slowly increase.  The chart does show, however, that for a while Neptune was our most distant planet. See how Pluto’s orbit was inside that of Neptune? Don’t forget, Pluto takes 248 earth years to get around the Sun once. These events hold generally true no matter where you are in the world, but they need to be fine tuned for your latitude. Folks in the southern hemisphere, for example, get a much better view of Saturn and Mercury early in the month, than those in the north.

Finding Uranus

Uranus can be found with binoculars – or in exceptional conditions the naked eye – but locating it is an advanced project for those already comfortable with finding the naked eye bright stars and asterisms. You need full darkness, your eyes should be dark adapted, and you should be in an area where light pollution isn’t a serious problem.  That said, finding this planet is relatively easy if you have a decent pair of binoculars and patience.  Here’s a chart to use. After reading the directions below, click on the chart to get a larger version.

This Uranus finder chart is for September, 2009, about two hours after sunset. It is meant to be used first with the naked eye, then binoculars. The red circle represents the typical view with wide field 7X or 8X binoculars. Included on this chart are many faint stars that can be seen only with binoculars. See text for instructions. Click on chart for larger view. (Made from Starry Nights Pro with modifications.)

Start your search by locating Jupiter and the Great Square. You may also see Fomalhaut, a first magnitude guidepost star that will be introduced in October.

Next look below the Great Square for the “Circlet.” This is a well-known asterism in the constellation Pisces – but in typical suburban skies it is a difficult object and you may be able to pick out just three of the brightest stars in it with your naked eye. In rural skies you should be able to see most of these stars with the naked eye, but try to locate them with binoculars. The entire Circlet probably will not fit in a single binocular field of view, but enough of it should so you know what you are seeing.

Now use your binoculars to try to locate the trapezoid of fainter stars below the Circlet. This little unnamed trapezoid will probably fit in your binocular field of view. The faintest star of these four is just a bit brighter than Uranus, so that gives you an idea of what you seek.

Finally, with your binoculars scan up and to the right (west)  of this trapezoid and you should pick up an arc of three stars all about the same brightness. The third – the highest – of these is Uranus. While you won’t see a disc, you may notice that it shines with a steadier light than the other two. This is typical of planets. In a good telescope Uranus will show a tiny disc and perhaps a greenish tinge, but to the casual observe may be easily mistaken for a star.

Finding Neptune

Neptune is both easier and harder to find than Uranus. Again, binoculars and a dark sky are needed. What makes it easier is it’s near Jupiter. What makes it harder, is it’s signifcantly fainter than Uranus – so faint that whether you see it or not will depend on how dark your skies are.  You will need this little finder chart, however, to pick it out of the starry background.

Finding Neptune requires binoculars, or a small telescope, and patience. Fortunately, Jupiter drops us right in the neighborhood! See text for complete directions - and click on chart to get an enlarged version. This charts is for mid-September, 2009, about two hours after sunset. Neptune will appear to move slightly towards Jupiter during the course of the month. (Made with screen shot from Starry Nights Pro. I added names and arrow.)

Step 1 – find Jupiter, the brightest “star” in the eastern sky. The red circle represents a widefield binocular view. Your binoculars may show a smaller field. Also see if you can spot the two bright stars in our chart that are to the left – east – of Jupiter. They are bright enough so you should be able to see them even in typical suburban skies. In any case, you certainly should be able to find them with binoculars by first locating Jupiter, then scanning to the left – eastward.

Step 2 – after locating the two bright stars, use binoculars to look for the arc of three dimmer stars above them. These three are about the same brightness as Uranus and just at the edge of naked eye visibility under excellent, dark skies. For most people this means they will be seen only in binoculars. Neptune is to their left – east – as indicated.

And for early risers – Venus and Mars!

A crescent moon and Venus dominate the morning sky in the east, along with Mars and half a dozen bright "winter" guidepost stars. Click chart for larger image. SLightly modified screen shot from Starry Nights Pro.

Don’t miss the autumnal equinox!

OK – if you’re in the southern hemisphere, this marks the start of spring. In the northern hemisphere, it’s autumn. In either case, it’s when the Sun crosses the celestial equator and day and night are almost of equal length.

The autumnal equinox this year is on September 22, 2009, at  21:28 Universal Time.

So what? Well, if you’re just starting out in star gazing, this is a great time to get your bearings at your observing site. That is, on or about September 22 – a few days either way won’t matter much – note where the Sun either rises or sets. That marks the due east – or due west – point on your horizon and from that you can easily figure out where north and south are.

It’s also the day on which the reading of your equatorial sundial switches from one plate to the other. That is, in the north you go from the north-facing dial plate to the south-facing (underneath) one.  See our equatorial wrist dial project. if you want to know more about this.

And finally, I find it cool that day and night are nearly of equal length. For one thing, that means the stars get a break. For the next six months here in the north we’ll have longer nights and thus more time to enjoy the night sky.