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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 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 November 2012 for the “Eye of Sauron” star and its “zombie” planet!

November brings us our southernmost – and northernmost – guidepost stars, Fomalhaut and Capella. And  fresh off the press of NASA for Halloween – a zombie planet! Now you see it – now you don’t – now you do!  But first, the normal.

The positions of Capella and Fomalhaut in the sky mean that for Northern Hemisphere observers Fomalhaut is the guidepost star we see for the shortest amount of time – and Capella is the one we see the longest.

In fact, for many, Capella is visible during some hour every night of the year – and for those north of latitude 45 degrees, it is circumpolar – that is, it never sets. But lonely – and freshly fascinating – Fomalhaut just puts in a relatively brief appearance low to the south.

From NASA:”This image, taken with the Advanced Camera for Surveys aboard NASA’s Hubble Space Telescope, shows the newly discovered planet, Fomalhaut b, orbiting its parent star, Fomalhaut. The small white box at lower right pinpoints the planet’s location. Fomalhaut b has carved a path along the inner edge of a vast, dusty debris ring encircling Fomalhaut that is 21.5 billion miles across. Fomalhaut b lies 1.8 billion miles inside the ring’s inner edge and orbits 10.7 billion miles from its star.” Click image for larger version.

Fomalhaut is “lonely” because there are few bright stars in its vicinity. It is “freshly fascinating” because early in this century the Hubble Space Telescope got a fantastic picture of a disc of “debris” surrounding it, showing this young star to be in the throes of forming planets. Then in 2008 scientists announced they had actually found a planet circling Fomalhaut (see photo above), the first planet outside our Solar System to be seen with visible light. Cool! Add to this the fact that the Hubble photograph of Fomalhaut could be easily mistaken for the Eye of Sauron, and for fans of the Lord of the Rings movie triology, Fomalhaut becomes especially memorable. (For more on the “Eye of Sauron” go here.)

But wait, this just in!

Vital stats for Fomalhaut (FO-mal-ought)

• Brilliance: Magnitude 1.16; its luminosity is the equal of 16 Suns.
• Distance: 25 light years
• Spectral Types: A3V
• Position: 22:57:39, -29:37:20°

After reading this description, click on the chart for a larger version. About an hour after sunset, November evenings offer us an eastern sky filled with a host of asterisms both large and small. A good starting point for the naked eye is the Great Square of Pegasus. From one corner of it you can find Andromeda’s Couch which ties into what I call the “Demon’s Triangle” because it is anchored by the eclipsing variable, Algol – the “Demon Star.” The “W” of Cassiopeia should be obvious – and there are three asterisms shown that are best seen with binoculars. The “Hockey Stick” and “Water Jug” should fit in a low power binocular field, while only half of the “Circlet” will fit. Capella anchors our chart to the north, with Fomalhaut to the south. I included Deneb Kaitos because while it is a little dimmer than Fomalhaut, it could be mistaken for it. Wait an hour or so and you’ll see brilliant Jupiter rise in the east to dominate this portion of the sky in 1012. (Prepared from Starry Nights Pro screenshot.)

Click here to download a printer friendly version of the above chart.

Finding Fomalhaut

As always, it’s easiest if you start looking in the east 45 minutes to an hour after sunset when in the twilight only the brightest stars are visible as shown on our chart. Fomalhaut is the brightest star south of southeast and about a fist and a half above the horizon 45 minutes after sunset. I emphasize “star” because a bit later int he evening in 2012 Jupiter is in the  east as well, but significantly brighter. Trailing well behind Fomalhaut – to the east – and lower still is a second magnitude star (same brightness as the North Star) called Deneb Kaitos. Don’t mistake it for Fomalhaut.

If you have learned the Great Square – see this post – then the two stars that form the western edge of that square can be used, as pointer stars. Drawing an arrow through those two stars leads you to Fomalhaut. You could also wait until a couple of hours after sunset when you would find Fomalhaut very close to due south. Even then, from my latitude of 41.5° N it is not quite two fists (19°) above the southern horizon.

Ahhh Capella!

Capella is distinctive because it’s not “a” star – it’s two! But these two, bright, yellow suns are so close together that you’ll always see them as one, even if you use a large telescope. Together they make a star that rivals Vega and Altair, now well into our western sky, in brightness. (See Summer Triangle chart here.) In fact Capella is the third brightest star in the Northern Hemisphere – but that’s a tad deceptive because it doesn’t count Sirius – the brightest star that most Northern Hemisphere observers can see, although technically Sirius is in the Southern Celestial Hemisphere, since it is below the celestial equator. But you don’t have to worry about such technicalities to enjoy a view of Capella. Just look near the horizon to the northeast. You will need a very clear horizon, however, especially at the start of the month because then Capella will not even be one fist above the horizon.

Just as Fomalhaut is a bit south of southeast, Capella is a bit north of northeast.

It’s easiest to find Capella if you start 45 minutes to an hour after sunset. Choose a spot with a clear horizon to the northeast and watch for a bright star to appear very near the horizon. Like all bright stars near the horizon, Capella will twinkle and flash in different colors because you are seeing it through a lot of atmosphere. It won’t show its soft, golden hue until it is much higher in the sky. Even a veteran skywatcher can be fooled by this. Recently my wife was looking to the northeast on a fall evening and saw what she thought was Capella. But it was so bright and blinking red and green so distinctly, that she changed her mind and decided it was an airplane! (There’s an airport off in that general direction.) When after a minute or so it hadn’t moved, she knew her first thought was correct – but boy it made a convincing airplane!

For me, Capella marks a graceful arc of bright stars and asterisms that circle the north celestial pole. If you have been following these directions for a few months, look at Capella, the “Bow” of Perseus, and the “W” of Cassiopeia to see what I mean. Watching these move in the course of a single night – or from month to month – always gives me a real sense of how, from our vantage point, all the stars appear to circle Polaris.

As mentioned, Capella is really a complex multiple star. Its two main components are both yellow giants dubbed Aa and Ab, but there are two more stars in this family. However, they are a pair of red dwarfs only visible in a telescope and are so far away from the two bright stars that they take more than 1,000 years to complete an orbit. The two bright stars orbit in just 104 days. James B. Kaler, in his book The Hundred Greatest Stars, says this about the Capella twins:

These two magnificent giants are separated by about the distance between Venus and the Sun. A resident on a ‘Jupiter’ ten times further out would see two ‘Suns’ about half a degree across (similar to the Sun in our own sky), separated at maximum by some 6 degrees, one setting right behind the other.
So when you find Capella, pause – picture yourself on the Jupiter-like planet with these twin yellow Suns in your sky!

Vital stats for Capella (kah-PEL-ah)

• Brilliance: Magnitude .08; its luminosity is the equal of 16 Suns.
• Distance: 42 light years
• Spectral Types: G8/G0
• Position: 05:16:41, +45:59:53

In this month’s chart I identify three relatively dim asterisms as good objects for your binoculars – there’s also the magnificent Andromeda Galaxy barely visible to the naked eye if you have very dark skies, but certainly a small blurry patch in binoculars. The arrows on the chart show two paths to tracking it down by star hopping. Found it? Pat yourself on the back. You are looking at about 300 billion stars and you are looking back in time about 2.5 million years!

The “Water Jug” of Aquarius is a nice binocular object. To me it looks just like a three-bladed airplane propeller.  The “Circlet” is part of Pisces and while quite faint, is easy to trace out in binoculars, though you will have to scan about a bit to see it all. It doesn’t fit in a single field of view – at least in most binoculars.

What I dub the “Hockey Stick” are the three brightest stars of Aries, the Ram. The faintest of these is an easy and beautiful double – a nearly perfectly matched pair if you have small telescope, point it at them and enjoy.

Still with us!

Other bright guide stars and asterisms introduced in previous months that are still readily seen include the Summer Triangle of Altair, Deneb, and Vega, which is high over head and crossing into the western sky. Arcturus is just above the horizon in the west, the Big Dipper just west of north and hugging the horizon, and the Teapot is diving into the ground in the southwest. And, of course, we have the “Bow” of Perseus with “Algol” the “Demon” star, the “W” of Cassiopeia, the “home plate” of Cepheus, Andromeda’s Couch, and the Great Square.

Look east In September 2011 – a pair of asterisms and three brilliant ‘guides’

There are three new asterisms this month – well, I’m not sure one of them should really be called an asterism. This third asterism is really just three stars that serve as a special marker for the equatorial coordinate system – so we’ll take that up last. As we travel September skies we’ll also move from the age of mythology to the age of science. To get started, here’s a chart of what you can expect to see in the east about an hour after sunset.

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

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 the constellation known as 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.”

The second asterism, 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 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 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 – thus the significant tie to the equatorial coordinate system.

If you’re not familiar with this system, it 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,” which is rising in the northeast on these September evenings. In the early evening in September this is the “top” star in the “W.” 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 in September 2011. 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 east In September 2010 – a pair of asterisms and three brilliant ‘guides’

There are three new asterisms this month – well, I’m not sure one of them should really be called an asterism. This third asterism is really just three stars that serve as a special marker for the equatorial coordinate system – so we’ll take that up last. As we travel September skies we’ll also move from the age of mythology to the age of science. To get started, here’s a chart of what you can expect to see in the east about an hour after sunset.

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

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 the constellation known as 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.”

The second asterism, 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 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 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 gap 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, and in the fall of 2010 there’s even a fifth – the bright planet Jupiter. They can all be tied together by a long, graceful arc that represents the great circle of zero hour right ascension – thus the significant tie to the equatorial coordinate system.

If you’re not familiar with this system, it 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 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,” which is rising in the northeast on these September evenings. In the early evening in September this is the “top” star in the “W.” 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.

And in September 2010, this same arc connecting Polaris, Beta Cassiopeia, Alpha Andromeda, and Gamma Pegasi points right to the most brilliant “star” on our eastern horizon, the giant planet Jupiter. This, of course, is true just for 2010, for like all good “wandering stars,” Jupiter will be moving on. But this month it serves as a special guide as well – more about that in the September “Events” post. Here’s a wider view to the east bringing in all these connections.

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 in September 2010. 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 other 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.

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.

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..

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 at the earth turns on its axis in the course of the night.

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 meant to be used firstw ith the naked eye, then binoculars. The red circle represents the typical view with wide field 7X or 8X binoculars. See text for instructions. Click on chart for larger view.

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 elarged version. (Made with screen shot from Starry Nights Pro. I added names and arrow.)

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.

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.

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