Sky, Eye, and Camera: Special Viewing/Photo Ops for September 2014

Note: This is my first installment of a new feature. It’s a modification of the old “events” post and still is a guide to special events for the month – things happening in the sky that do not repeat from month to month but are special to a particular date. To this I have added – and put emphasis on – information about events that are particularly suitable for capture as photographs – especially photographs that convey a sense of being there and are taken with ordinary cameras.  This is in contrast to the traditional astronomy images that use special cameras to show us things we cannot see with the naked eye by taking long exposures and gathering much more light, usually using a telescope as the lens. Greg Stone

 

September 2014 gives us several special opportunities for nice, naked-eye views of stars and planets that also provide excellent photo opportunities, especially if you have a DSLR camera – or something similar where you can adjust the exposure.

August 2014 "super" Moon. (Photo by Greg Stone)

August 2014 “Super” Moon. (Photo by Greg Stone) Click image for larger version.


September 8, 2014 – “Super” Moon rising in the Earth’s Shadow/ Belt of Venus

I can’t get real excited about the “Super” Moon idea – we’ve had two this year already, and they’re really not all that unusual, or for that matter not quite as “super” as the word makes them sound.

But the full Moon rising is always a pretty sight and a very easy subject for photographers. One alert, though. The Moon is really quite small – half a degree – and so your picture may show a Moon much smaller than you remember seeing with the naked eye. This is because the full Moon  ALWAYS appears to be much larger to us when it’s near the horizon, whether “super” or not. A friend asked me recently why my picture of the Moon conveyed this sense of what he saw, while others didn’t.

The answer is simple. I used a small telephoto lens. Technically it was an 80mm, but because of the sensor on my camera, you have to add a factor of 1.6 to that to get the 35mm – or “full frame” equivalent. So in this case it was like using a 128mm telephoto on a 35mm camera.  Lots of simple cameras come with zooms that provide at least that much magnification. Use more magnification and you may end up with a real nice picture – but it may make the Moon look a lot bigger than what people saw with their naked eye.

That brings me to another major point. My whole approach to night sky photography is to try to convey a sense of being there. For that reason I don’t overdo the sensitivity of the CCD – that is, I don’t set the ISO real high – and I do keep the exposures relatively short. With the full Moon in August, I had the ISO set at  1600 – which meant I had a little noise to clean up with the editing software – and I could take the-picture at 1/160th of a second – that’s fast enough to hand hold even with the 128mm telephoto – and the the F-stop was 7.1, small enough to provide some reasonable depth of field.

That last is critical. The Moon is at infinity, but you want to also include some foreground subjects at close and mid-range to give a sense of proportion to the objects in the sky.

Moon rise time varies by your location. Where I am on the eastern seaboard of the US, the Moon will be rising roughly 20 minutes before the Sun sets on September 8th. This is going to provide an interesting  opportunity, I think, to catch the Moon in the shadow of the Earth and/or the Belt of Venus. These appear in the east shortly after sunset and after about 15 minutes start melding into the night. The shadow will be a darker blue than the sky above it and extend perhaps a fist above the horizon.  The “Belt of Venus” will be a rosy band above the shadow. Bottom line: I think the most interesting shots will be taken about 10-15 minutes after sunset.

Of course, much depends on local weather conditions. For me the trick is to know where the Moon will be rising – just a tad south of east in September 2014 – and find a spot that not only gives me a clear horizon in that direction, but also provides some interesting foreground objects to go along with the Moon.

September 20, 2014 – Algol at minimum brightness

This event – an eclipse of Algol – will be centered on 10:55 pm EDT; on the 17th a similar event will center on 11:06pm PDT. I’m not going to go into  detail about the “demon star” here. If you don’t know about it, you can read more in this earlier post.

What I do want to point out is it’s fun to see this star dim, then brighten over the course of a few hours, and if you like taking constellation pictures, it would be neat to get one of Perseus with Algol at full strength and one with Algol at full eclipse.

While these eclipses happen every few days, you’re lucky if you find one or two a month that come at a time convenient for you to watch – and then, of course, the weather has to cooperate.

September 22, 2014 – the  Fall Equinox

This is a fun time to get a picture of either sunrise or sunset. You don’t need to be right on this date -a day or two before or after will do fine. The basic idea is to show the Sun in relation to local landmarks and thus identify for yourself the general heading for east or west from any given spot.  Actually, a real nice project is to pick a scenic spot, take a picture of a sunrise or sunset as close to the Equinox as you can get, then do the same thing again from the same spot showing the Sun at the Winter and Summer Solstices and at the Spring Equinox. The four will then show the movement of the Sun along the local horizon in the course of a year.

September 24-30 – Mars and its Rival, Plus Saturn

Click for larger version - prepared from Starry Nights Pro screenshot.

Click for larger version – prepared from Starry Nights Pro screenshot.

I suggest you go out an hour after sunset and look southwest for three bright “stars” near the horizon. Two should have a reddish hue, one a yellowish hue – though honestly, with them all this close to the horizon the atmosphere may cause them to twinkle and change color.

Still, this is worth seeing and should provide an interesting photographic challenge. However, if you have been taking pictures of constellations, similar settings should work here. (I like to set the ISO at 6400 and expose for four seconds at F7.1 with the camera on a tripod, of course, and using a cable release. This, for me, gives a typical naked eye view – but you need to experiment. I also clean up the background noise in such photographs using Lightroom.)

The main attraction here is that Mars – the red planet – is near Antares, a red star. In fact, the name “Antares” means “rival of Mars” because its color rivals the obviously ruddy planet.  Saturn is farther away but has a distinctly yellowish hue. In the course of these six evenings, Mars will first draw a bit closer to Antares, then get farther away. Saturn will also get lower each night, though Mars is moving in a counter direction right now and will appear to hold its altitude – that is, be at the same height at the same time. Of course, all of these will get too close to the horizon and eventually set, so timing is important. I plan to start an hour after sunset, then see what works best over the next half hour or so as the sky gets darker, but Antares, Mars, and Saturn also get lower.

Again, the challenge for me is to include foreground objects and show the night sky as we really experience it.  Here’s a shot, for example, that I took last winter of Orion – with a quite bright Moon out of the picture to the left.

Orion as seen from the Town Farm in Westport, MA in the winter of 2014. (Photo by Greg Stone)

Orion as seen from the Town Farm in Westport, MA in the winter of 2014. (Photo by Greg Stone)


Crescent Moon and Planets  in September 2014

I see two photo opportunities to capture a crescent Moon near major planets. On September 20, 2o14, the Moon should be within about 6 degrees of Jupiter, both about one-third the way up the eastern sky an hour before dawn. As Jupiter fades, Venus may put in an appearance near the horizon, though it’s getting quite close to the Sun.

On September 27, 2014, Saturn will have an even closer encounter with the Moon in the southwestern sky at dusk. Yep – this is in the middle of the period suggested to capture Antares, Mars, and Saturn – so if the weather gives you a break you might get a crescent Moon as a bonus.

 

Look east In September 2014 – 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 wodnerful collection of five related mythological figures - Cepeheus (king), Cassiopeia (queen), Andromeda (princess), Perseus (hero), and Pegasus, the flying horse. (Developed froma screen shot of  Starry Night Pro. Click for larger version.)

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 from 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.   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.

Prepared from a Starry Nights Pro screen shot - click for a larger version.

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 lie on aline that is the starting point for placing a grid on the sky to create a precise address for each star in terms of its relation to  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 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 north in July 2014 and take the measure of your skies and eyes!

Light pollution is a big issue these days. How does it impact you? Summer is a good time to check by looking north about two hours after sunset and seeing what stars you can see in and near the Little Dipper. Why summer? Because this is when the Little Dipper should be highest in your sky – standing upwards from Polaris, the North Star. Here’s what you should see on a typical July evening when you look north from mid-northern latitudes.

In summer the faint stars of the Little Dipper are high above the North Star. Click image for larger view. (Developed from Starry Nights Pro screen shot.)

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

The Big Dipper is diving downward in the northwest but is still very high, and its handy “pointers” should get you quickly to the North Star, Polaris. Roughly opposite the Big Dipper you should see the “W” of Cassiopeia starting to make its way upward in the northeast. And unless you suffer from really terrible light pollution, you should see the two “Guardians of the Pole” – the second and third magnitude stars that mark the end of the Little Dipper. The brighter of these two is just a tad dimmer than Polaris, but since it’s higher in the sky right now and thus shining through less air to get to you, it will probably look just the same as the North Star in brightness.

To do this test you first have to wait until it is genuinely dark, and in summer that’s a bit longer than in winter. Twilight actually is divided into three steps. We have civil twilight which goes from sunset until when the Sun is six degrees below the horizon. Nautical twilight is the next period, which continues until the Sun is 12 degrees below the horizon. Then you have Astronomical Twilight until the Sun is 18 degrees below the horizon. At that point it is as dark as it will get and will remain that dark until we run the sequence in reverse as the eastern horizon nears the Sun. As a rough rule of thumb, you can consider each twilight period to last half an hour – but the exact length depends on where you are on Earth and the time of year. If you want to get precise, go to the U.S. Naval Observatory site, fill in the form you’ll find there, and you can get a table that will give you the start and end of these twilight times – or for that matter when the Moon rises, or the Sun sets. It’s very handy. (Note: the preceding link takes you to a page for US cities and towns – but there’s a second page here where you can put in the latitude and longitude for any location in the world, including in the US. )

The second thing you need to do is make sure your eyes are dark adapted. They are casually reasonably well dark adapted after you have been out for 15 minutes and have not looked at any white lights. But it can take from half an hour to an hour of protecting your eyes from any white light for them to become fully dark adapted. That doesn’t mean you have to sit around in the dark doing nothing waiting for this to happen. In the last hour or so before full darkness there are plenty of things to see – just avoid bright lights. That also means moonlight. You’re going to want to do this when the Moon is not in the sky, for it will make it difficult to see faint objects anywhere near it. In July of 2014 the last two weeks should work pretty well for the evening hours – as will the first day or two of the month.  Other evenings, the Moon will dominate the early evening sky.   (A good Moon-phase calendar can be found here, though for this purpose I find the table from the Naval Observatory for local Moon rise is also handy!)

So here’s the test:

How many stars can you see in the Little Dipper?

Remember that in the magnitude system the higher the number, the fainter the star.

The Little Dipper consists of seven stars. Three are easy – Polaris and the two “Guardians” marked “21” and “30” on the chart below. If, once you are dark adapted, you can see only one of the “Guardians,” then your skies are limited to magnitude 2 stars and brighter – very poor. If you see both, but no other stars in the Little Dipper, then your limit is magnitude 3.

On our chart below, the magnitude of each star is listed as a whole number so as not to put decimal points on the chart because they might then be confused with faint stars! So when you see a star listed as “21” that means “magnitude 2.1.”

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

Even in good, dark skies the other four stars in the Little Dipper may not be that easy to see – and the faintest ones may require averted vision – that is, don’t look exactly where the star should be. Instead, look a little to one side or the other, and the star may pop into view. That’s because the center of your eyes are not as sensitive to faint light as the outer regions of your eyes.

Here’s another little trick that may help you locate these faint stars – use binoculars. With typical, hand-held binoculars you may be able to fit all four stars of the Little Dipper’s “cup” into the same field of view. If not, get the “Guardians” in your field of view, then move just a little to where the other two stars of the “cup” should be. This does not count, of course, for the light pollution test. For that test we’re trying to determine the faintest star you can see with the naked eye. But looking first at the stars with binoculars helps assure you that they really are there! You also can trace out the handle this way, though you will have to move your binoculars to do so.

If you can locate all the stars in the Little Dipper with your naked eye, you have very dark skies – congratulations. To see how good they are – and continue to test your eyesight and dark adaption – look for the stars marked “55” and “60” on our chart.

The star marked “60” is traditionally thought of as the faintest you can see with your naked eye. That’s a magnitude 6 star. In really pristine skies, such as those over Mauna Kea in Hawaii, experienced observers with excellent eyes can detect stars down to magnitude 8 with the naked eye. Personally, I’m happy when I can see all the stars in the Little Dipper and especially happy if I can get that “55” star – I’ve never seen the “60” one with my naked eye. But relative to the heavily light-polluted eastern seaboard of the US, I have dark skies.

This is not simply a good guide to light pollution in your area. It also is a handy guide to tell you just how good  – how “transparent” – the skies are on any given night – and to show you how well you have dark adapted at any given moment. So whenever I go out to observe I frequently glance at the Little Dipper to test both my developing night vision and the clarity of the skies. (It never fails to amaze me how much and how quickly my night vision changes. )

To the casual observer all clear nights are equal. But the experienced star gazer knows they are not, and the stars in and about the Little Dipper are a good guide, especially in the summer months when they are so high in the sky.

Look Southeast in July 2014 – Colorful Stars and Planets, Great Asterisms – even a Great Constellation!

We’re going to cheat a little this month and look quite a bit south of east, rather than due east. The reason is we have some wonderful stars getting as high as they get if we look that way – AND we have two bright planet and colorful planets, Saturn and Mars which make for some interesting comparisons with nearby stars. We also have a couple of really cool asterisms and even a great constellation.

I’m not a big fan of constellations. Most don’t look anything like their names imply; some are quite obscure; and many simply can’t be seen in typical suburban skies these evening because of light pollution. Scorpius is an exception. It looks like the Scorpion of its name – a truly beautiful constellation with its graceful, curving tail. What’s more, many of its brighter stars actually do hang out together – they are not just an accident of our line of sight.

The Scorpion as Bayer saw him in his 1603 illustrated star atlas, Uranometria. Click for a much larger image. (Used by permission from the Linda Hall Library of Science, Engineering & Technology.)

It dominates our southeastern sky in July, just as the Summer Triangle – a terrific asterism, dominates our eastern sky this month. And we have two fascinating new “guide” stars – the intriguingly close and rapidly spinning Altair – and the incredibly huge and red Antares that is right at the heart of the Scorpion!

Antares begs comparison with Mars – both being red. But Mars is also very, very close to a bright blue star, Spica. Mars will be just a bit brighter than either of these comparison stars. Saturn –  between Mars and Antares and also very bright, has a yellowish hue.

But the real treat at this time of year remain these southern stars. They never get real high and from mid-nothern latitudes we only get a couple hours on a summer night when they are really well in view above the southern horizon. To top it all off the Milky Way runs from Deneb in the  Summer Triangle to the tail of Scorpius,but you have to wait a couple hours after sunset before this comes out.

Let’s take a look at the chart, then examine Scorpius along with its quaint little companion, a very real looking teapot complete with “steam” coming out of its spout! Wow! Summer nights may be short, but they sure offer some nice visual treats!

Oh - about that "teapot." We won't discuss it, but you can clearly see it tagging behind the scorpion. If you have real clear skies, the Milky Way is beautiful in this area and looks like steam rising from the teapot. More on this next month. Meanwhile, click image for a larger version. (Developed from a Starry Nights Pro screen shot. )

Click to enlarge! This chart covers a bigger section of sky then we usually show. Vega, for example,  will be six fists up. Oh – about that “teapot.” We won’t discuss it, but you can clearly see it tagging behind the scorpion. If you have real clear skies, the Milky Way is beautiful in this area and looks like steam rising from the teapot. More on this next month.  (Developed from a Starry Nights Pro screen shot. )

First up is the Summer Triangle – it’s an asterism that you can’t miss, and it will grace our evening skies right up into early winter. If you’ve been following for a few months, you’ve already met its lead star, brilliant Vega. And last month we were introduced to Deneb on the other corner. In fact, we saw that we could make a quite impressive Northern Triangle out of Deneb, Vega, and Polaris. But far better known than that asterism is the Summer Triangle shown above of Vega, Deneb, and Altair.

Altair is hard to miss. It is the brightest star low in the east early on a July evening, but it is also distinctive because it has two reasonably bright companions, close on either side, that form a straight line with it. This is appropriate because it’s not hard to see Altair and those two companions as representing an eagle in flight, and that’s good because they are the major stars in a constellation known as Aquilla, the Eagle.

Altair is white, much like Deneb and Vega, and is even closer to us than Vega. Vega is 25 light years away, Altair just 16. That’s in contrast to Deneb, which you may recall is an astounding 1,425 light years (at least)  from us – astounding because even at that distance it is almost as bright as its much closer companions and some experts believe it is much more distant.

Altair also distinguishes itself by spinning incredibly fast. It takes our Sun almost a month to complete a rotation on its axis. Altair, almost twice as large as our Sun, spins once on its axis in just 10 hours. Why, I don’t know, but it’s one more reminder of how these stars, which all look pretty much the same to us because they’re so far away, all have their special traits that distinguish them as individuals.

The most obvious special trait for Antares, our other new guide star this month, is its redness – and it’s one of only four guide stars that is quite close to the ecliptic – the path of the planets. That means that reddish Mars comes close, sometimes, to reddish Antares, and that’s appropriate because the name “Antares” actually means “like Mars.” However, science tells us something else about Antares. It is huge. I mean BIG.

Get out your calculator and do a little simple math. (OK, I’ll do the math, but really – this is simple, and I think you would appreciate the numbers much more if you did the calculations yourself.) One possible source of confusion:  To visualize a sphere I use its diameter. To actually calculate things I need the radius – since a radius is half of a diameter  you’ll find me jumping back and forth between these two terms – don’t let it confuse you.)

So try this. Start with something manageable, like the Earth. It’s about 8,000 miles in diameter and that’s a number that’s fairly easy to imagine. Let’s reduce Earth to a ball 2 inches in diameter. It would have a radius, then, of one inch.

Now let’s make a scale model Sun to go with our Earth. That’s easy. The radius of the Sun is 109 times the radius of the Earth. That means the Sun will have a radius of 109 inches – roughly 9 feet. So now we have a one-inch Earth and a 9-foot Sun. So our scale model has two balls – one two inches in diameter to represent the Earth and one 18 feet in diameter to represent the Sun.

That certainly should tell you that the Sun is a lot bigger than Earth, but my problem is, these linear measures don’t give us a really good sense of the size difference. We need to visualize spheres in terms of volume. We can get a rough approximation of the  volume  of a sphere by simply cubing the radius and multiplying it by 4. If we do this for our scale model Earth we have (1 x 1 x 1) x 4 – or four cubic inches. Now to calculate the volume of our scale model Sun – in cubic inches – we multiply 109 x 109 x 109, then multiply that by 4. Wow! Well, if you tried it on your calculator I hope you said “Wow!” You should get 5,180,116. That means you can fit well over one million Earths in our Sun! That to me is a lot more impressive than the linear measure where we find the diameter of the Sun is about 109 times the diameter of Earth.

Now let’s do a similar exercise with Antares. Antares has a radius more than 800 times the Sun. Do the math. Our scale model Sun has a radius of  9 feet – our scale model Antares will have a radius in feet of 9 x 800. Man, that’s big. About 7,200 feet!  (Just remind yourself that a mile is 5,280-feet.)  So now we have three models – a 2-inch diameter Earth, an 18-foot diameter Sun, and a 14,400-foot diameter Antares – that last is approaching three miles!

Don’t bother to calculate the volume. Unless you use scientific notation, your calculator probably won’t handle it. But you get the idea. That little dot of red light we call Antares is B-I-G. And don’t forget – on this same scale the huge planet you are standing on is just 2-inches in diameter.

Here’s a graphic representation courtesy of Sakurambo:

Notice the artist didn’t even attempt to represent the Earth on this scale!

Think of it this way. If Antares were our star, both the Earth and Mars would be orbiting inside it!

That’s huge – even bigger than Deneb – which we noted last month was a “supergiant” – the same class that Antares belongs in. But Deneb would only reach about halfway to Earth – Antares would go past both Earth and Mars. Deneb, however, is a very young, very bright, very hot star, which is why it shines so brightly from such a great distance. Antares is much closer – about 600 light years vs at least 1,425 for Deneb. But Antares is old – a star in its dying stages, and is large and bright because it is so bloated. It really is quite cool as stars go – that’s why it appears red to us. But it has such a huge surface area that even from a distance of 600 light years it appears bright to us – a bit brighter in our sky than Deneb, actually.

So let’s briefly consider these four guide stars together – Vega is our “standard” star – white, about the size of the Sun, and quite close at 25 light years. Altair has some unusual features, but is still rather normal as stars go. Deneb is distinguished by being large and hot; Antares by being even larger, but relatively cool.

Vital stats for Altair (AL-tair), also known as Alpha Aquilae:

• Brilliance: Magnitude .77; its luminosity is the equal of 11 Suns.
• Distance:16.8 light years
• Spectral Types: A, main sequence
• Position: 19h:50m:47s, +08°:52′:06″

Vital stats for Antares (an-TAIR-ease), also known as Alpha Scorpii:

• Brilliance: Magnitude 1.09; its luminosity is the equal of 65,000 Suns.
• Distance: 600 light years
• Spectral Types: M, supergiant
• Position: 16h:29m:24s, -26°:25′:55″

Events, June 2014 – Bright Lights Along the Ecliptic this Month

This is a great month to become familiar with the ecliptic in our sky. The ecliptic is the plane of our solar system where you will always find the Sun, Moon, and Planets.

Finding it sounds simple – and it is if you pick your time and date. The problem is it changes constantly because the Earth is tilted on its axis and revolving around the Sun.  I should stress one more thing – the ecliptic is not the path you will see the Sun, Moon, and planets take across the sky in a given night – it is the path they will follow as they change position over days, weeks, and even years. How quickly an object follows this path depends on how close it is to us – the Moon makes it completely around the ecliptic each month, the Sun each year – but a distant planet, such as Saturn, takes about 30 years.

You can trace the portion of this path visible about an hour after sunset on a June night in 2014. For the chart below I chose June 13th simply to include a nearly full Moon in the picture. It will, of course, change position each night – but the planets will stick pretty close to these general spots all month. So go out an hour or so after sunset and start your search by looking to the northwest for brilliant Jupiter. It will be brighter than any star, or any of the other planets and only about 10 degrees above the horizon – ten degrees can be measured by holding your closed fist at arms length.

Jupiter thus achors the western end of the ecliptic. We’ll move eastward to trace out the rest of it.

Click on this chart to get a much larger version. (Prepared from Starry Nights Pro screen shot.)

Click on this chart to get a much larger version. (Prepared from Starry Nights Pro screen shot.)

 

Up above Jupiter are the famous Gemini Twins – the nearer and slightly brighter one is Pollux, the other is Castor.

Turn a bit south of west you will find the bright star Regulus. While it outshines most other stars visible tonight, it is just in between Castor and Pollux in brightness and is about 30 degrees above the horizon – three fists.

Next on our list is the red planet Mars – the second brightest object on our chart. If you’re not detecting the rusty redness of it, try looking at it in binoculars. Then compare it with the next bright star on our chart, Spica. Spica is a  little lower than Mars an quite a bit dimmer. (Mats is four fist high, Spica about three and half.) Spica, however, is a very hot – and thus very blue – star. Look at the difference in color between it and Mars.

Moving eastward you’ll find Saturn, whose beautiful rings will show in even a small telescope. However, to the naked eye and binoculars Saturn simply looks like a bright star – not as bright as Mars, but certainly brighter than Spica. It has a pale, yellowish hue.

Continuing to the east is Antares, just 15-degrees – a fist and a half – above the horizon.  It’s name means “rival to Mars” and for good reason – it is a classic, red star, rivaling the color of Mars.  Again, contrast its color with that of Spica and Mars.

Oh – high overhead is the bright star Arcturus. It’s about as bright as Saturn and nearly 70 degrees above the horizon – seven fists.  Do you remember how to find Arcturus? You “follow the arc” of the Big Dipper’s handle – now high in our northern sky, to Arcturus, then “drive a spike” to Spica.

What else is going on this month?

Well, two dates to keep in mind:

The Summer Solstice is June 21 at 6:57 am EDT – and thus begins the longest day of the year.

On June 24 a thin crescent Moon will be very close to the brightest of planets, Venus in the eastern sky about an hour before sunrise. Should be a pretty sight and a nice picture opportunity.

Look East in June 2014 and see if you can make the stars “pop!”

How can we make the stars pop out of the sky and into our mind’s eye?

That’s the perennial problem for me, for what we actually see is so much less than what is actually there that we can’t help but belittle the stars unintentionally. This month’s guide star, Deneb, is a prime example. It’s easy to spot using our chart as it rises in the northeast below and to the left of Vega. In terms of our bright guide star list, Deneb’s rather dim – 19th in the list of brightest stars we see with the naked eye. But that reveals much more about our point of view than about Deneb. Deneb, plain and simple, is one of the most luminous stars in our galaxy. Vega, just above and to the right of it in the northeast, looks so much brighter – but it isn’t. It’s simply so much closer. Vega is just 25 light years away.

Deneb, by one the most recent calculations, is 1,425 light years from us. (This is still open to debate and some put it nearly twice that far away!) But we’ll use the 1,425 light year figure. Put Deneb in Vega’s place – just 25 light years away –  and it would be visible in broad daylight! Does that help it “pop?”

When astronomers talk about how “luminous” a star is they don’t mean how bright it appears to us in our night sky. They mean how bright it actually is. In fact, frequently they use “luminous” to include all the radiation that comes from a star – even radiation in wavelengths that we don’t see, such as infrared and ultraviolet. They then compare a star’s luminosity with the luminosity of the Sun – the Sun being “1.” When they examine Deneb that way they get a luminosity of 54,400 Suns – awesome! (Popping yet? Can you imagine our Sun being twice as brght as it is? three times a bright? How about 54,400 times brighter?)  But when we look at Deneb we see a star that is just moderately bright – magnitude 1.25.

Prepared from Starry Nights Pro screen shot - click for larger version.

Prepared from Starry Nights Pro screen shot – click for larger version.

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

OK – let’s get serious about this popping business. When you look at Deneb, you have to use your mind’s eye to see it for what it really is, not just for what it appears to be. So what should we see when we look at Deneb? First we should see something huge. Deneb is classed as a “supergiant.” So sit back and try to imagine a star whose diameter is 108 times that of the Sun. No, wait! First imagine how big the Earth is. Then get in your mind the fact that the Sun is 109 times the diameter of the Earth. Got that? Now try to imagine that Deneb is to our Sun what our Sun is to the Earth. birdshotBut wait! I really do not want to talk about diameters. Those are for people who live in a flat world. Think in terms of volume, because that’s what a planet or star really is – a volume – a mass formed into a sphere. To get your mind around volume, picture the earth as a tiny bird shot just 2.5mm in diameter. Here’s one to give you the idea. Now picture a sphere about 10.5 inches in diameter – a basketball would be close, or this glass garden globe. See the difference? When talking diameters, the Sun is 109 Earths. But when you’re talking volume, you could fit well over a million Earths inside the Sun. sun_deneb Now think about the same thing in terms of Deneb. That little lead shot is our magnificent Sun. The blue globe is Deneb! That’s what you should see in your mind’s eye when you watch this month’s guide star rise in the northeast. Were Deneb our Sun, its surface would reach halfway to the orbit of Earth and needless to say, Earth would be in a hopelessly hot location. But there’s more, of course. Size is a great starting point, but it doesn’t equate with mass. A lot of stars are bloated – that is, their mass is spread out over a large area and they have a huge surface area from which to radiate a tremendous amount of energy. That is the case with Deneb. It is believed to be about 10-15 solar masses, but its total luminosity – the total amount of energy it radiates when compared to the Sun is a whopping 54,400 times that of the Sun! Wrap your mind’s eye around that! That’s why astronomer/author James Kaler writes that Deneb is

among the intrinsically brightest stars of its kind (that is, in its temperature or spectral class) in the Galaxy. If placed at the distance of Vega, Deneb would shine at magnitude – 7.8, 15 times more brightly than Venus at her best, be as bright as a well-developed crescent Moon, cast shadows on the ground, and easily be visible in broad daylight.

Deneb is unusual for supergiant stars for it is of spectral Class A – that means it’s your basic white star and very hot as stars go. Other very large stars, such as Betelgeuse, are in a different stage of development and quite cool and red to the eye. Deneb is believed to be just 10 million years old. That’s very young in terms of star ages. Our Sun is believed to be 5 billion years old. Deneb will never get to that ripe old age. Massive stars such as Deneb live in the fast lane, burning up their core hydrogen fuel relatively quickly. Kaler gives this analysis:

The star is evolving and has stopped fusing hydrogen in its core. However, it’s hard to know just what is going on. It might be expanding and cooling with a dead helium core and on its way to becoming a red supergiant, or it might have advanced to the state of core helium fusion. Having begun its life as a hot class B (or even class O) star of 15 to 16 solar masses just over 10 million years ago, its fate is almost certainly to explode sometime astronomically soon as a grand supernova.

Kaler certainly knows what he’s talking about, but don’t bother to keep a “death watch” on Deneb. “Astronomically soon” means some time in the next 100 million years or so ;-) Sherlock Holmes once chided his companion Watson saying “you see, but you do not observe.” With the stars, we have to take our cue from Holmes. We have to go beyond merely seeing. And in truth, we have to go beyond merely observing. We have to take the knowledge the scientists have given us and somehow apply it to what we see, so with our mind’s eye we truly observe. Only then can we pop Deneb out of that “twinkle, twinkle little star” category and see it for what it really is.

Vital stats for Deneb (DEN-ebb), also known as Alpha Cygni:

• Brilliance: Magnitude 1.24; its luminosity is the equal of 54,400 Suns. • Distance: 1,425 light years • Spectral Types: A2 supergiant • Position: 20h:41m:26s, +45°:16′:49″

Guide star reminder

Each month you’re encouraged to learn the new “guide” stars rising in the east about an hour after sunset. One reason for doing this is so you can then see how they move in the following months. Deneb and the Northern Cross join several other guide stars and asterisms in the June sky. Again, if you have been reading these Posts for several months, be sure to find the stars, asterisms, and planets you found in earlier months. Early on a June evening these will include, from east to west, the following: Deneb, Vega, Arcturus, Spica, Saturn, Leo’s Rump (triangle),  the Sickle, Regulus, the Beehive, and in the northwest getting near the horizon, Pollux and Castor. You may also see Capella very near the horizon. For more experienced observers looking to extend their knowledge of the skies this month, I highly recommend trying to track down two more asterism – the Northern Crown and the KeystoneOK, technically the Northern Crown (Corona Borealis) is a constellation. But I always apply the name to the handful of moderately bright stars that look like a half circle – a crown. As the chart below shows, these two asterisms are located on a line between Arcturus and Vega and they sort of divide that line into thirds. As with our guide stars and other asterisms, they will help you if you advance to finding other more interesting objects int he night sky with binoculars and telescope.

keystone-crown

For a printer-friendly version of this chart, click here. The Crown itself can provide you with an interesting test of how dark your skies are since a couple hours after sunset on a June night it is well up in your eastern sky. It consists of a circlet of seven stars which can just fit within the field of view of wide-field binoculars – the example below shows an eight degree circle. It may be helpful to look at these stars with your binoculars, even if they don’t all fit in the same field of view at once. But to test how dark your skies are – and how transparent they are at the moment – wait until your vision is dark adapted, then see how many of these stars you can see. The numbers beside the stars are the magnitudes in decimals as given by Starry Nights software. However, I’ve followed the convention of not using a decimal point, since it might be mistaken for another faint star. So “41” means magnitude 4.1, for example. If you are seeing all seven stars you can be happy with your skies and these light-polluted times. In a truly dark location, however, this will be easy – but sadly such locations are rare these nights.

Read text above for explanation of how to use. Thenc lick on image to give you a larger view and luse the link below to download a printer friendly version. (Made from Starry Nights screen shot.)

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

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