• Choose a month

  • Rapt in Awe

    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.

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 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″

Look East in July 2013 – Great Stars, Great Asterisms – even a Great Constellation!

Well, a “great constellation” if you look southeast. 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 becauseo f 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! Let’s take a look at the chart first, then examine these stars along with their 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!

Incidentally, in 2013 Saturn is the bright “star” just off our chart to the west – follow the curve of the scorpion’s body upwards and you can’t mix it – it pairs up with the blue guidepost star, Spica, a bit more to the west.

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. )

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. )

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

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″

Look East in July 2012 – Great Stars, Great Asterisms – even a Great Constellation!

Well, a “great constellation” if you look southeast. 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 days. 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! Let’s take a look at the chart first, then examine these stars along with their 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. )

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

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 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 from us – astounding because even at that distance it is almost as bright as its much closer companions. 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 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″

Luna-See – Let the Moon of August 2011 be your guide!

Anyone can find the Moon – so why not use it to help you learn the sky?

Moon and Mars in the early morning sky, August 25, 2011.

Each month the Moon in its travels comes near some planets, bright stars, and asterisms. If you look on the right night this month you’ll be able to use the Moon to help you find:

  • Saturn and Spica (August 2, 3 & 4)
  • Antares and the Scorpion (August 7)
  • The Arrowhead with the asteroid Vesta (August 13)
  • The Hockey Stick and Jupiter (August 19)
  • Pleiades, Hyades, & Aldebaran (August 22)
  • Taurus (August 23)
  • Mars with the heavenly twins, Castor and Pollux (August 25)

Whew! That’s a whole lot.  And you’ll find when and exactly where to look by using the charts below. You have to pick the right night and you have to  be ready to approximate – the charts are a rough guide as to when and where to look – and use binoculars to help you find otherwise bright stars because the Moon light will tend to wash out  all but the brightest.

I say “rough guide” because these charts are all for my specific location on the Northeast Coast of the United States. The moon moves about half a degree (its diameter) an hour, so observers on the West Coast will see it in a little different location than I do. But the charts should give a good general guide and help you know the night sky better – and as a bonus you’ll begin to develop a feel for the rather complex motion of the Moon each month.

Notice that for the first half of the month the Moon is in the early evening sky. For the second half it is in the morning sky. The Moon’s image in the charts is about three times as big as it actually is in order to show the phase clearly.

Click any chart to get a larger version. All charts are prepared from Starry Nights Pro screen shots.

Saturn and Spica, (August 2, 3 & 4)

Antares and the Scorpion (August 7)

The Arrowhead with the asteroid Vesta (August 13)

The Hockey Stick and Jupiter (August 19)

Pleiades, Hyades, & Aldebaran (August 22)

Taurus (August 23)

Mars with the heavenly twins, Castor and Pollux (August 25)

Moon phases

  • New Moon  – July 31
  • First Quarter – August 6
  • Full – August 13
  • Last Quarter -August 21
  • New Moon – August 28

Look East in July 2011 – Great Stars, Great Asterisms – even a Great Constellation!

Well, a “great constellation” if you look southeast. 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 days. Scorpius is an exception. It looks like the Scorpion of its name – a truly beautiful constellation. 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! Let’s take a look at the chart first, then examine these stars along with their 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. )

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

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 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 from us – astounding because even at that distance it is almost as bright as its much closer companions. 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 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 Sun is about 109 times the diameter (or 109 times the radius) 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 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″

Coloring the stars – an exercise for all seasons

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

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

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

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

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

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

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

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

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

You can download a version for printing by clicking here.

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

Your task is simple.

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

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

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

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

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

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

More about a star’s spectral class

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

Oh Be A Fine Girl/Guy Kiss Me

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

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

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

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

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

What we can surmise from the colors

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

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

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

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