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) 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.

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)

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!

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. )

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″

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.)

 

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! Drive a Spike to Spica (pronounced Spy-ka) and two planets in May 2014!

If you followed “the arc” of the Big Dipper ‘s handle last month to find Arcturus, then you “drive a spike”  this month to find Spica –  pronounced Spy-ka – plus Mars and Saturn. It’s like taking a long, cool slide from the Dipper – and the “Arc-to-Arcturus” and “Spike-to-Spica” relationships hold true as long as these stars are in our skies – which will be right through August.

Here’s how it looks – remember: look east  starting about an hour after Sunset.  Arcturus, Spica, and Mars should all be visible as the first stars emerge, but Saturn will have to wait a bit. At the start of the month it may be too low until about two hours after sunset – but each night it rises earlier and earlier. On May 10 it is in opposition, rising as the sun sets.

Click to enlarge. (Prepared from Starry Nights Pro screen shot.)

Click here to download a printer-friendly version of this chart.

While the Dipper is easy to recognize, its stars are second magnitude – bright, but easily out-shone by the triangle of Arcturus, Mars, and Saturn. Even Spica, almost exactly magnitude 1, is brighter than the Dipper stars. Still, the Dipper stars will be very high in the northeast and easy to spot as it gets dark.  The brightest star in this section of the sky is Arcturus at magnitude minus 0.04. (Remember, the lower the magnitude number, the brighter the object – minus magnitude are brighter still.) The next brightest star you’ll see is over to your left, low in the northeast – Vega at magnitude 0.04. So Vega is barely on the plus side of  magnitude  zero and Arcturus is barely on the minus side, a difference that is next to impossible to detect with the eye. This year both these stars will be out shone by Mars, almost magnitude -1,  and Saturn is just a tad dimmer than Arcturus and Vega, though about a full magnitude dimmer than Mars.  Together these  five –  Mars, Arcturus, Vega, Saturn, and Spica will give you a good sense of the magnitude scale. In fact, throw in Polaris – the North Star, which is almost exactly magnitude 2 and you have a range of four magnitudes represented – quite a brilliant display.

The color contrast is exceptional here too. As these stars and planets get higher in the sky, you will notice that Mars is definitely reddish, Spica is a rich blue, while Saturn has a yellow tint.

We dealt with Arcturus last month. Saturn will be in our sky all night and as always is a treat for the small telescope user. From a naked eye perspective,  it’s fun to remember that the name “planet” means “wanderer” in Greek, but all “wanderers” are not created equal. Mars, Venus, and Mercury move  so quickly in our night sky that you can easily mark their changes over a period of a few days -certainly a week.  Saturn is much more sluggish.

Saturn changes position over the course of an entire year by roughly 12 degrees.  To see this in the sky , find Saturn. Hold your fist at arms length so Saturn is just below it. Just above your fist is where Saturn was last year. Put Saturn on top of your fist and just below your fist is where it will be next year. So how long will it take Saturn to get around the sky to roughly the same position? Well, 360/12 = about 30 years!  Now if you think a moment, the Moon takes about 30 days to get around our sky – and that means the Moon moves each day about 12  degrees –  the same apparent distance covered by Saturn each year.  All of which should tell you that it would be reasonable to assume Saturn is much farther away from us than the Moon – which, of course, it is.

None of this is rocket science, but I find it interesting to contemplate as I look up and see Saturn. I measure that distance it will travel in the next year and in my mind’s eye I stand above the Solar System and I see a long thin pie slice reaching from me to Saturn’s distance orbit and this helps me keep things in perspective – gives me a better intuitive feel for the neighborhood in which we live.  OK – for the record Saturn is moving at about 22,000 miles an hour, Mars about 54,000 miles an hour in a much shorter orbit, and we’re whipping right along close to 67,000 miles an hour – and we don’t even feel the wind in our face! Oh – and Saturn’s actual orbital period is 29.458 years.

On to this month’s new guidepost stars!

Vega and Spica are each fascinating stars, but let’s start with Vega. Shining brightly not far above the northeastern horizon as the evening begins, Vega comes about as close to defining the word “star” as you can get. In “The Hundred Greatest Stars” James Kaler calls it “the ultimate standard star” because its magnitude is about as close to zero as you can get  and its color is about as close to white as you can get. (If you’re one of those who assumed all stars are white, you’re forgiven. Individuals vary in their ability to see different colors in stars and for everyone the color differences are subtle – in fact I think of them as tints rather than colors. )

It’s hard not to be attracted to Vega when you read Leslie Peltier’s wonderful autobiography, “Starlight Nights.” Vega was central to his astronomical observing throughout his career because he began with it when he first started reading the book from which I got the idea for this web site, “The Friendly Stars” by Martha Evans Martin. Peltier wrote:

According to the descriptive text Vega, at that very hour in the month of May, would be rising in the northeastern sky. I took the open book outside, walked around to the east side of the house, glanced once more at the diagram by the light that came through the east window of the kitchen, looked up towards the northeast and there, just above the plum tree blooming by the well, was Vega. And there she had been all the springtimes of my life, circling around the pole with her five attendant stars, fairly begging for attention, and I had never seen her.

Now I knew a star! It had been incredibly simple, and all the stars to follow were equally easy.

Vega went on to be the first target of the 2-inch telescope he bought with the $18 he made by raising and picking strawberries. (This was around 1915.) And Vega became the first target for every new telescope he owned until his death in 1980. If you still don’t know a star, go out and introduce yourself to Vega early on a May evening. Even without a plum tree to look over, you can’t miss her! And once you’ve done that you’re well on your way to making the night sky your own.  (And yes, Vega is the star from which the message comes in Carl Sagan’s book/movie “Contact.”)

Vital stats for Vega, also known as Alpha Lyrae:

• Brilliance: Magnitude .03 ; a standard among stars; total radiation is that of 54 Suns.
• Distance: 25 light years
• Spectral Type: A0 Dwarf
• Position: 18h:36m:56s, +38°:47′:01″

Spica, a really bright star – honest!

Spica is truly a very bright star, but the numbers you may read for its brightness can have you pulling your hair. That’s because there are at least four common ways to express the brightness of Spica and other stars, and writers don’t always tell you which way they’re using. So let’s look at these four ways and see what they mean for Spica.

The first is the most obvious. How bright does it look to you and me from our vantage point on Earth using our eyes alone? We then assign it a brightness using the magnitude system with the lower the number, the brighter star. (For full discussion of this system, see “How bright is that star?”)

By this measure Spica is 16th on the list of brightest stars and is about as close as you can come to being exactly magnitude 1. (Officially 1.04) Though I should add here that the number really marks the midpoint of a magnitude designation – that is, any star that is in the range of magnitude .5 to magnitude 1.5 is called “magnitude 1” and so on for the other numbers on the scale.

But that scale talks about what we see. It doesn’t account for distance. Obviously if you have two 60-watt light bulbs and one is shining 6 feet away from you and the other 1,000 feet away, they are not going to look the same brightness. But if we put them both at the same distance – say 100 feet – they would look the same. So it is with stars. To compare them we pretend they all were at the same distance – in this case 10 parsecs, which is about 32.6 light years. Put our Sun at that distance and it would be magnitude 4.83. (That’s about as faint as the fainest stars we see in the Little Dipper.) We call that its absolute magnitude.

The absolute magnitude for Spica is -3.55 – not quite as bright as dazzling Venus.

Wow! That’s pretty bright compared to our Sun! Yes it is. Sun 4.83; Spica -3.55. Don’t miss the “minus” sign in front of Spica’s number! That means there’s more than eight magnitudes difference between the Sun and Spica. And that relates to the next figure you are likely to see quoted. Something that is called its luminosity. Luminosity compares the brightness of a star to the brightness of our Sun. Unfortunately, the term is often misused – or poorly defined. Thus in the Wikipedia article I just read on Spica it said that “Spica has a luminosity about 2,300 times that of the Sun.” Yes, but what does that mean? It means that if we were to put the two side by side, Spica would appear to our eyes to be 2,300 times as bright as our Sun.

That is bright! But there’s more, much more. Spica is also a very hot star – in fact one of the brightest hot stars that we see with our naked eyes. But we miss most of that brightness because most of it is being radiated in forms of energy that our eyes don’t detect. In the case of Spica, that is largely ultraviolet energy. The Wikipedia article actually listed Spica’s luminosity twice, and the second time it gave it as “13,400/1,700.”

Oh boy – now we have Spica not 2,300 times as bright as the Sun, but more than 13,000 times as bright. Now that IS bright – but is it right? Yes! So why the difference? Again, the first “luminosity” given – 2,300 times that of the Sun – is measuring only what we can see with our eyes. The second is measuring total amount of electromagnetic radiation a star radiates and is properly called the “bolometric luminosity.” And why two numbers for that last figure? 13,400/1,700? Because while Spica looks like one star to us, it is really two stars that are very close together and one is much brighter than the other. So what we see as one star is really putting out energy in the neighborhood of 15,100 times as much as our Sun.

This can get confusing, so I suggest you remember three things about Spica.

1. It defines first magnitude, having a brightness as it appears to us of 1.04.

2. It is really far brighter (magnitude -3.55), but appears dim because it is far away – about 250 light years by the most recent measurements.

3. It is very hot – appearing blue to our eyes – and because it is very hot it is actually radiating a lot more energy in wavelengths we don’t see, so it is far, far brighter than our Sun.

Spica is the brightest star in the constellation Virgo, one of those constellations where you can not really connect the dots and form a picture of a virgin unless you have an over abundance of imagination. Besides, the remaining stars are relatively faint. That’s why we focus on the bright stars and sometimes those simple patterns known as “asterisms” and use them as our guides.

Vital stats for Spica, also known as Alpha Virgo:

• Brilliance: Magnitude 1.04; a close double whose combined radiation is the equal of 15,100 Suns.
• Distance: 250 light years
• Spectral Types: B1,B4 Dwarfs
• Position: 13h:25m:12s, -11°:09′:41″

Guideposts reminder

Each month you’re encouraged to learn the new “guidepost” 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. If you have been reading these posts for several months, you may want to relate Spica to two earlier guidepost stars with which it forms a right triangle, Arcturus and Regulus.

Once you have identified the Right Triangle, note carefully the positions of Spica and Regulus. They pretty much mark the “ecliptic.” This is the path followed by the Sun. Also, within a few degrees north or south of it, you will find the planets and the Moon. That’s well illustrated in 2014 by the presence of both Saturn and Mars, very near the ecliptic, as noted on our chart.

Arcturus and Regulus are not the only guidepost stars and asterisms in the May sky. Again, if you have been reading these posts for several months, be sure to find the stars and asterisms you found in earlier months. Early on a May evening these will include, from east to west, the following: Arcturus, Spica, Saturn, Leo’s Rump (triangle), The Sickle,  Mars, Regulus, the Beehive, Procyon, Sirius, Pollux, Castor, and in the northwest near the horizon, Capella, and the Kite. Venus will be a bright evening “star” in the west, and if you look early in the month you may catch a glimpse of Sirius and Betelgeuse before they set.

Events April 2014: Mars, the Moon, and the Earth’s Shadow – Yes, a Total Lunar Eclipse !

 

Love those Lunar eclipses, but who was in charge of the scheduling for this one? Some insomniac like me, no doubt, for on the East Coast of the USA where I live this thing really doesn’t pick up steam until about 2 am April 15, then continues until near when the Moon sets just before dawn. The West coast residents get a somewhat more timely view.

Here’s the schedule for those in the Eastern Daylight Time zone on the morning of April 15:

1:57 am partial eclipse begins

3:06 am totality begins

3:45 am mid-eclipse

4:25 am totality ends

5:33 am partial ends

The Moon sets about the time the Sun rises, which varies according to location. (Eclipses happen at the same time all over the world – but of course what time that is for your location depends on your time zone – and for some, the Moon simply won’t be in your sky during the eclipse hours.  For a complete guide to where this eclipse can be seen and when for your location, see the NASA eclipse pages.

There’s an incredible NASA eclipse Javascript on this page that delivers all sorts of eclipse data and time for anywhere in the world – however, I did notice that the times were  standard – so you need to adjust for daylight savings if relevant.

What adds a special touch to this eclipse is that Mars will be pretty close to the Moon from the time the Moon rises near sunset. I always like watching the fainter stars come out as the Moon goes into total eclipse, then slowly vanish as it comes back. But with this eclipse, Mars will provide a special treat with it’s ruddy hue shining brighter than any of the nearby stars – though Arcturus and Spica will both rival it.  Here’s a chart for my location – the same relationships will apply anywhere, but those farther west will see the orientation of the chart shift since the Moon and stars will be higher in their sky at this point.

 

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

 

The Scorpion should be beautiful on the southern horizon. For me the Moon is about 22 degrees above the southwest horizon at this point. If you have trouble finding it – eclipses vary on how dark they get, then simply look for Mars and Spica – if you get Spica in binoculars the Moon will be in the same field about 2 degrees east of it.

April Planet Parade

No, you can’t see the Moon – it’s eclipsed! (Actually, it can be quite red and fairly easy to see – or it can be quite dark and difficult to see during totality. ) Click image for larger view. (Made from screen shot of Starry Nights Pro.)

Jupiter is high in the western sky all month, setting in the wee hours of the morning; by the end of the month it sets closer to midnight, but is still brighter than any star or any other planet in the evening sky.

However, Mars rivals Jupiter, taking over in the eastern sky in the early evening hours and remaining visible all night throughout April. It’s in retrograde motion this month, which means it appears to climb a bit higher in our sky as the month goes on, moving west against the background of stars. This is the best opportunity for two years for telescope users to get a good look at Mars.

Saturn gets high enough to view in the eastern sky about three hours after sunset at the start of the month, and two hours after sunset by the end of the month.

Venus is best seen low in the east about 45 minutes before sunrise, and on April 25th has a nice pairing with the crescent Moon. While Jupiter is brighter than any star, Venus is two magnitudes brighter than Jupiter, so it shows up well even though it is well into morning twilight before it is high enough to see easily. I like finding pretty spots to try to capture the crescent Moon, Venus, and foreground landscape  in twilight.  Here’s a shot I got at the Town Farm in Westport MA when there was a similar  arrangement of the Moon and Venus in March 2014.

Click image for larger view.

 

A Meteor Sprinkle

The annual Lyrids meteor “shower” is not nearly as intense as the Perseids in August or the Geminids in December, but if the night is clear it could be fun. It is supposed to peak (roughly 20 meteors per hour) on April 23 when a  waning crescent Moon will rise after 3 am and start to interfere some.

I must admit that with a shower like this I take it casually. That is, I go out and observe other things, but I keep an eye out for meteors, and if I see one, I try to trace its path backwards to see if it points in the general direction of the constellation Lyra – if it does, I assume it’s part of the shower and not a random meteor. You might see a shower meteor a few days before or after the peak, and it might come at any time of night in any part of the sky, but if I were going to pick an hour to keep a sharp eye out for Lyrids, it would be between 2 am and 3 am on the morning of April 23.

The Lyrids are believed to be remnants of Comet Thatcher, which orbits the Sun about every 415 years.

 

 

Events for March 2014: Planet Sandwich Seasoned with a Sprinkling of Zodiacal Dust

Two realities – The image above gives you an idea of the true size and look of the planets visible in March skies. (From left, Venus, Earth, Mars, Jupiter, Saturn) That’s one reality. What you see with your naked eye is much different.  Planets look like stars – though very bright ones  and some with distinctive hues.

At dusk Jupiter dominates the night sky high overhead –  think of it as one slice of bread for our sandwich. During morning twilight Venus dominates the sky low in the east – that’s the other slice. Between we have Mars on the evening side of midnight and Saturn on the morning side of midnight.

The “seasoning” – Zodiacal Light  – is interplanetary dust that forms a soft cone of light rising out of the west about 80 minutes after sunset – but is only visible if your skies are dark enough.

In total this makes a tasty show at any time of night to supplement the annual,  ever-advancing march of the stars. Here’s where and when to look.

The Zodiacal Light is the most challenging and can’t compete with the Moon’s light, so it’s available for the first two nights of the month, then comes into view again starting on the 18th and going for the rest of March, 2014.  To see it you need a clear sky to the west with no light pollution in that direction. You also need to allow your eyes to dark adapt. for 20 minutes. What you’re looking for is something roughly akin to the Milky Way in brightness, but in a soft pyramid shape that starts out wide as it rises from the horizon and leans to the south as it reaches one-third or more up the sky in the general direction of Jupiter. It’s really quite an amazing feature.

If you see it, reflect on this explanation from Wikipedia:

The material producing the zodiacal light is located in a lens-shaped volume of space centered on the Sun and extending well out beyond the orbit of Earth. This material is known as the interplanetary dust cloud. Since most of the material is located near the plane of the Solar System, the zodiacal light is seen along the ecliptic. The amount of material needed to produce the observed zodiacal light is amazingly small. If it were in the form of 1 mm particles, each with the same albedo (reflecting power) as Earth’s Moon, each particle would be 8 km from its neighbors.

For the metrically-challenged (that includes me) that means one dust particle every five miles! In the light of that information, it’s absolutely awesome if you see any thing at all!

Highly recommended that you click this image for larger version. Hard to see the stars otherwise.

Jupiter  is on top these March nights, sharing the same general area of sky as the Gemini Twins. I took the picture (above) of it in late February – it’s position in March won’t change much, though it will get a little dimmer, it will still be much brighter than any star. As always, it’s fun to see if you can hold your binoculars steady enough to detect one of its four largest Moons. When it’s high like this you’re looking through less air and they may be easier to spot – but then, it’s a  bit hard on the neck to look so high in the sky while holding binoculars.

Again. to see any of Jupiter’s Moons your eyes have to be dark adapted, its best to use the largest, most powerful binoculars you can hold, such as 10X50, and you need an idea what to expect. The moons will be roughly in line with Jupiter’s equator – but at any given moment the number visible will vary, as will their distance from the planet, and which side they may be on. (They can all be on one side, they can be split two to a side, etc.) Jupiter together with its Moon – even when they are most distant, are only going to take up about 1/20th of the typical binocular field.

Here’s the sort of thing you are hoping to see:

How Jupiter’s moon might appear at one specific moment – in this case a moment when they were all on the same side of the planet. Of course the next night the view could be quite different. The letters stand for Europa, Io, Ganymede, and Callisto.

If this is your first time looking for the moons, do yourself a favor. Go to this page at the Sky and Telescope Web site and open the JavaScipt utility. It will tell you right where the moons are – and which is which – for any given moment.

As Jupiter dims a bit during the month, Mars becomes quite bright reaching magnitude -1.3 by the end of the month, and shines with a distinctive reddish hue. That’s  almost as bright as Sirius, but is no challenge to Jupiter, both of which appear white.

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

It rises about 3.5 hours after Sunset at the start of the month, but comes up during evening twilight at the end of the month. Generally it will be well placed for naked eye observing about an hour after it rises – those with small telescopes may want to wait another hour or two for a better view. That’s why I see it primarily as a late evening object.

You’ll find it by looking to the east about four hours after sunset as March begins. The Big Dipper will be high in the northeast. Follow the curve of it’s handle down to the bright star Arcturus. Continue this curve and you will come to Mars, roughly five degrees from the bright blue star, Spica. (Remember: When low on the horizon bright stars and planets will appear to sparkle and change color because you are looking through so much air.) While these relationships will remain the same, as the month goes on Mars will be rising earlier and earlier.

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

Saturn still is best seen in the early morning hours, though it rises just before midnight in the southeast. I think the best guide to it is the triangle it forms with Arcturus and Mars. Of the three corners of this triangle, Saturn is dimmest, shining with a soft yellowish light. However, it still outshines the stars in its vicinity.

You can’t miss Venus if you’re up an hour before sunrise. It actually comes up a couple hours before sunrise and in morning twilight is well above the southeast horizon an hour before sunrise. At about magnitude -4.7 (it gets a bit dimmer towards the end of March) it simply outshines everything except the Sun and Moon, so there’s no mistaking it and no difficulty finding it. Just look in the right general direction at the right time.

On March 27, 2014 a very thin, waning crescent Moon should fit in the same binocular field with Venus roughly three degrees up and to the left.

August 2013 – last good look at Saturn, and a Moon-free Perseids shower

The Big Dipper’s handle can guide you first to bright Arcturus, then to yellowish Saturn and blue Spica – both will be about the same brightness. Venus is much brighter, but best seen about half an hour after sunset when it is about 10 degrees above the western horizon. By an hour after sunset it is half that or less and even if you have an unobstructed horizon, may be lost in mist and twilight. CLick for larger image. (Prepared from Starry Nights Pro screen shot.)

For a printer friendly version of the above chart, click here.

If you have a small telescope, August 2013 will give you your last good look at Saturn for the year and if you live on the right side of the globe – not where I live – the Perseids  meteor shower should be spectacular this year with no interference from a waning Moon.  Venus, meanwhile, continues to reign low in the western sky just after sunset.

The sky north of east early on the morning of August 12, prime time to watch for Perseids meteors. (Created from a Starry Nights Pro screenshot.)

For a  printer friendly version of the above chart click here.

The Perseids should reach their peak on August 12 at about 19:00 UTC. To find what time that is for your region, go here.  For about half the world that’s good news, for the other half it’s bad because you really want to see this shower in the early morning hours and you will get the best show if the shower’s peak falls during those hours for your time zone.

Locally, on the East Coast of the United States, I’m going to watch the weather and if either the morning of August 11 or the morning of August 12 is forecast to be clear, I plan to start observing about 2 am. But I am not expecting a big Perseids show – just a nice summer night with a much better chance than usual of seeing a bright meteor.

Meanwhile, I’m bracing myself to hear a lot of promotional blather about the Perseids locally from TV weather folks and others who should know better, but the truth is in North America the timing of this year’s shower could hardly be worse.  The shower is best for a couple hours either side of its peak and its peak is forecast to come at 19 hours GMT on August 12 – for Eastern Daylight Time that translates to 3 pm – broad daylight.  What’s worse, even if the peak was in the early evening hours, the Perseid’s radiant point doesn’t get high in the sky until the early morning. That’s why the best time to see Perseid meteors – regardless of the peak time – is still  between midnight and  a couple hours before dawn.

So can we in America hope to see any Perseids at all? Yes, of course we can.  Just don’t expect a “shower.” In fact, I have to say that i always wince a little at the times and rates of meteors frequently given in news reports. Hey, just the word “shower” implies a lot more than most people usually see, especially from their typically light-polluted back yards.  When someone reports that the Perseids will peak at better than 100 meteors an hour, they usually fail to mention that three conditions have to be met for you to see that peak.

1. You need the Perseids radiant point to be nearly directly overhead – for EDT that occurs in a twilight sky, but is reasonably high from midnight on. The meteors may appear in any part of the sky, but they will appear to radiate from that point, so the higher it is, the better chance we have of seeing a meteor.

2. You need very dark skies – skies that will allow you to see magnitude 6.5 stars, if you are going to experience those real high rates. I have never experienced such dark skies, but they certainly exist. However,  with my reasonably dark skies I am very happy when I can detect a star of magnitude 5.

3. And, of course, you need the shower’s peak to coincide with the radiant point being very high in your sky.

One more caution – anything can happen. This is a forecast and usually reliable. But there could be a burst of meteors at a different time. You may get lucky.

And if all these  condition aren’t met for your location? Well, it’s reasonable to expect to see a Perseid meteor about every 10-15 minutes – of course you  may get two or three in a row hardly separated at all, then not see another one for  an hour. But be patient and you will get results – just not the meteor spectacular that some reports will imply. Last year they were coming in at a rate of 15-20 an hour four hours either side of the peak.

And yes, a Perseid can show up days either side of the peak.  How will you know it’s a Perseid? Draw a mental line extending the path of the meteor back towards the Perseid’s radiant point. If your line points back to that area of the sky – see map above – then you saw a Perseid. But there are always strays around – random meteors that have no connection to the shower – and at this time of year we have a couple weaker showers that may produce a few meteors going in other directions.

Meteors and meteor showers are fun if for no other reason than they are a chance to see something happening in the sky. Much of what we look at doesn’t change – or rather changes so slowly we don’t notice the change. Meteors, on the other hand, demand that you be looking in the right place at the right time. Only on the very rare, very bright meteors do we actually have time to alert others and have them turn their heads and see what we see.  And what we see is a space event happening closer to us than any other natural one. What’s more, meteors can have real scientific value.  They are viewed by some as our cheapest “space probe.” They are relatively pristine bits of matter left over from the early days of the solar system and so can tell a story to those who know how to read them.

Meteors – “falling stars ” – can be seen any time. You don’t have to wait for a “shower” like the Perseids; you just have to be lucky. But they are most frequent at certain times in the year when the Earth happens to be plowing through a meteoroid-rich area.  We call this occasion a meteor shower. (For your dictionary: A meteoroid is a small bit of space rock that becomes a meteor when it collides with our  atmosphere and heats to incandescence as it descends towards Earth. When it gets here – which is rarely as anything except fine, incinerated dust – it is a meteorite. )

The reason for a shower such as the Perseids is that we are passing through the debris trail of a comet. Think about it. The general model for a comet is a “dirty snowball,” and as that dirty snowball nears the Sun it melts, and as it melts it leaves a trail of dirt particles behind it – particles that remain in orbit until something like the Earth sweeps by and captures some of them with its gravity.

The comet itself can vanish entirely – but the result is a river of space dust – a river that is most intense nearest where the comet actually was.  That’s why there are some years – the 1990s in the case of the Perseids – when the meteor shower is more intense than others.  Now we are in a period when we are passing through the trail of the comet that creates the Perseids at a point where that trail is relatively sparse – so there will simply be fewer Perseids than there were  15-20 years ago.

That trail is not encountered all over the sky. It collides with our atmosphere near a particular point in our sky. That point is called the radiant – you might think of it as a hole through which the Perseids fall – and in the case of the Perseids, it appears to be in the constellation Perseus.  But we don’t see all the meteors at this point. We see a meteor only when its collision with our atmosphere is intense enough to make it burn up. The faint meteors we see are made by a speck of dirt about the diameter of a pencil lead. The brightest ones are caused by something about the diameter of the pencil’s eraser.  In either case it will, for all practical purposes, burn up entirely in our atmosphere – 50 to 75 miles up – and nothing significant will remain for anyone to find on Earth. But exactly where it burns up is another thing. That’s why we will see a sudden flare – a falling star – anywhere in the sky.

And that’s awesome! Consider this: If someone struck a match 50 miles away would you see it?  Yet a grain of sand, hurtling into the atmosphere, shows us such a brilliant light we can’t miss it! Why? Well, for one thing it is hitting our atmosphere at something in the order of 133,000 miles an hour – that makes a “speeding bullet” look like the proverbial turtle!

When you are watching for Perseids, you don’t have to look near the radiant point, though you will see more there.  A meteor can flare up suddenly anywhere and appear to draw a short (usually 5-10 degrees long) straight line across the dome of the sky. (Bright ones may actually leave a trail, which you can see for a few seconds with the naked eye or longer with binoculars.) If we trace a line backwards along the meteor’s trail we will see it comes from the area near the radiant point.

In the early evening, that Perseid radiant point is low in the northeast. That means nearly half the meteors that are radiating from it are happening below our eastern horizon. That’s why the shower is best in the early morning hours when the radiant is high in our sky. If the radiant is overhead, then we have nearly doubled our chances of seeing a meteor.

There are many meteor showers in the course of a year and some are better than others. The Perseids is one of the most reliable ones and happens to come at a convenient time for northern hemisphere observers when it is comfortable to be out at night, lying on the ground, and looking up.

In the final analysis there’s only so much time you can spend lying on your back gazing at the starry sky; though I very much enjoy that time, it’s made much more enjoyable by knowing that at any instant there’s a heightened likelihood that I will see a bright meteor.  That – and the summer Milky Way – make looking for Perseids in a dark and moonless sky always worth the effort for me.

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. )

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! Drop off the slide to Spica and land on Saturn in May 2013!

If you followed “the arc” of the Big Dipper ‘s handle last month to find Arcturus, then you can do the same this month to find Spica – it’s like taking a long, cool slide from the Dipper – and if you hop off just before just before the end, this year you’ll land on Saturn!

Here’s how it looks – remember: look east  starting about an hour after Sunset.  But don’t wait too long – as the night goes on, everything will appear to rise and after a few hours this chart won’t be much help.

Start with the Big Dipper, high overhead tot he east. Following the arc of its handle, slide down to the brightest star int he east, Arcturus. Soften your slide and keep going and you’ll come to another bright star, Spica. Hopwever, if you hop off the slide just before getting to Spica, you’ll land on Saturn – which will be brighter than Spica, but not quite as bright as Arcturus.

Click here to download a printer-friendly version of this chart.

While the Dipper is easy to recognize, its stars are second magnitude – bright, but not the brightest. The brightest star in this section of the sky is Arcturus at magnitude zero. (Remember, the lower the magnitude number, the brighter the object.) The next brightest star you’ll see is over to your left, low in the northeast – Vega. In fact, Vega is magnitude  zero as well and the difference between it an Arcturus is next to impossible to detect with the eye. And this year we can say the same about Saturn  – it is over near  Spica and will outshine it by just a tad and be nearly as bright as Vega and Arcturus. All of these – Arcturus, Vega, Saturn, and Spica will be brighter than any of the Dipper stars.

As these stars get higher in the sky, you will notice that Spica is a rich blue, while Saturn has a yellow tint. About an hour after sunset Vega will be the lowest at about 20-degrees above the horizon – two fists held at arms length. Saturn will be about 23 degrees above the horizon, Spica about 30 degrees, Arcturus 47 degrees and Alkaid, the star at the end of the big Dipper’s handle, about 64 degrees.

We dealt with Arcturus last month. Saturn will be in our sky most of the night and as always is a treat for the small telescope user. From a naked eye perspective,  it’s fun to remember that the name “planet” means “wanderer” in Greek, but all “wanderers” are not created equal. Mars, Venus, and Mercury move  so quickly in our night sky that you can easily mark their changes over a period of a few days -certainly a week.  Saturn is much more sluggish.

Look at the chart and you’ll see how little Saturn changes position over the course of an entire year – it moves roughly 12 degrees.  To see this in the sky , find Saturn. Hold your fist at arms length so Saturn is just below it. Just above your fist is where Saturn was last year. Put Staurn on top of your fist and just below your fist is where it will be next year. So how long will it take Saturn to get around the sky to roughly the same position? Well, 360/12 = about 30 years!  Now if you think a moment, the Moon takes about 30 days to get around our sky – and that means the Moon moves each day about 12  degrees –  the same apparent distance covered by Saturn each year.  All of which should tell you that it would be reasonable to assume Saturn is much farther away from us than the Moon – which, of course, it is.

None of this is rocket science or in any way  profound, but I find it interesting to contemplate as I look up and see Saturn. I measure that distance it will travel in the next year and in my mind’s eye I perch above the Solar System and I see a long thin pie slice reaching from me to Saturn’s distance orbit and this helps me keep things in perspective – gives me a better intuitive feel for the neighborhood in which we live.  OK – for the record Saturn is moving at about 22,000 miles an hour, Mars about 54,000 miles an hour in a much shorter orbit, and we’re whipping right along close to 67,000 miles an hour – and we don’t even feel the wind in our face! Oh – and Saturn’s actual orbital period is 29.458 years.

On to this month’s new guidepost stars!

Vega and Spica are each fascinating stars, but let’s start with Vega. Shining brightly not far above the northeastern horizon as the evening begins, Vega comes about as close to defining the word “star” as you can get. In “The Hundred Greatest Stars” James Kaler calls it “the ultimate standard star” because its magnitude is about as close to zero as you can get (.03) and its color is about as close to white as you can get. (If you’re one of those who assumed all stars are white, you’re forgiven. Individuals vary in their ability to see different colors in stars and for everyone the color differences are subtle – in fact I think of them as tints rather than colors. )

It’s hard not to be attracted to Vega when you read Leslie Peltier’s wonderful autobiography, “Starlight Nights.” Vega was central to his astronomical observing throughout his career because he began with it when he first started reading the book from which I got the idea for this web site, “The Friendly Stars” by Martha Evans Martin. Peltier wrote:

According to the descriptive text Vega, at that very hour in the month of May, would be rising in the northeastern sky. I took the open book outside, walked around to the east side of the house, glanced once more at the diagram by the light that came through the east window of the kitchen, looked up towards the northeast and there, just above the plum tree blooming by the well, was Vega. And there she had been all the springtimes of my life, circling around the pole with her five attendant stars, fairly begging for attention, and I had never seen her.

Now I knew a star! It had been incredibly simple, and all the stars to follow were equally easy.

Vega went on to be the first target of the 2-inch telescope he bought with the $18 he made by raising and picking strawberries. (This was around 1915.) And Vega became the first target for every new telescope he owned until his death in 1980. If you still don’t know a star, go out and introduce yourself to Vega early on a May evening. Even without a plum tree to look over, you can’t miss her! And once you’ve done that you’re well on your way to making the night sky your own.  (And yes, Vega is the star from which the message comes in Carl Sagan’s book/movie “Contact.”)

Vital stats for Vega, also known as Alpha Lyrae:

• Brilliance: Magnitude .03 ; a standard among stars; total radiation is that of 54 Suns.
• Distance: 25 light years
• Spectral Type: A0 Dwarf
• Position: 18h:36m:56s, +38°:47′:01″

Spica, a really bright star – honest!

Spica is truly a very bright star, but the numbers you may read for its brightness can have you pulling your hair. That’s because there are at least four common ways to express the brightness of Spica and other stars, and writers don’t always tell you which way they’re using. So let’s look at these four ways and see what they mean for Spica.

The first is the most obvious. How bright does it look to you and me from our vantage point on Earth using our eyes alone? We then assign it a brightness using the magnitude system with the lower the number, the brighter star. (For full discussion of this system, see “How bright is that star?”)

By this measure Spica is 16th on the list of brightest stars and is about as close as you can come to being exactly magnitude 1. (Officially 1.04) Though I should add here that the number really marks the midpoint of a magnitude designation – that is, any star that is in the range of magnitude .5 to magnitude 1.5 is called “magnitude 1” and so on for the other numbers on the scale.

But that scale talks about what we see. It doesn’t account for distance. Obviously if you have two 60-watt light bulbs and one is shining 6 feet away from you and the other 1,000 feet away, they are not going to look the same brightness. But if we put them both at the same distance – say 100 feet – they would look the same. So it is with stars. To compare them we pretend they all were at the same distance – in this case 10 parsecs, which is about 32.6 light years. Put our Sun at that distance and it would be magnitude 4.83. (That’s about as faint as the fainest stars we see in the Little Dipper.) We call that its absolute magnitude.

The absolute magnitude for Spica is -3.55 – not quite as bright as dazzling Venus.

Wow! That’s pretty bright compared to our Sun! Yes it is. Sun 4.83; Spica -3.55. Don’t miss the “minus” sign in front of Spica’s number! That means there’s more than eight magnitudes difference between the Sun and Spica. And that relates to the next figure you are likely to see quoted. Something that is called its luminosity. Luminosity compares the brightness of a star to the brightness of our Sun. Unfortunately, the term is often misused – or poorly defined. Thus in the Wikipedia article I just read on Spica it said that “Spica has a luminosity about 2,300 times that of the Sun.” Yes, but what does that mean? It means that if we were to put the two side by side, Spica would appear to our eyes to be 2,300 times as bright as our Sun.

That is bright! But there’s more, much more. Spica is also a very hot star – in fact one of the brightest hot stars that we see with our naked eyes. But we miss most of that brightness because most of it is being radiated in forms of energy that our eyes don’t detect. In the case of Spica, that is largely ultraviolet energy. The Wikipedia article actually listed Spica’s luminosity twice, and the second time it gave it as “13,400/1,700.”

Oh boy – now we have Spica not 2,300 times as bright as the Sun, but more than 13,000 times as bright. Now that IS bright – but is it right? Yes! So why the difference? Again, the first “luminosity” given – 2,300 times that of the Sun – is measuring only what we can see with our eyes. The second is measuring total amount of electromagnetic radiation a star radiates and is properly called the “bolometric luminosity.” And why two numbers for that last figure? 13,400/1,700? Because while Spica looks like one star to us, it is really two stars that are very close together and one is much brighter than the other. So what we see as one star is really putting out energy in the neighborhood of 15,100 times as much as our Sun.

This can get confusing, so I suggest you remember three things about Spica.

1. It defines first magnitude, having a brightness as it appears to us of 0.98 – closer than any other star to magnitude 1.

2. It is really far brighter (magnitude -3.55), but appears dim because it is far away – about 250 light years by the most recent measurements.

3. It is very hot – appearing blue to our eyes – and because it is very hot it is actually radiating a lot more energy in wavelengths we don’t see, so it is far, far brighter than our Sun.

Spica is the brightest star in the constellation Virgo, one of those constellations where you can not really connect the dots and form a picture of a virgin unless you have an over abundance of imagination. Besides, the remaining stars are relatively faint. That’s why we focus on the bright stars and sometimes those simple patterns known as “asterisms” and use them as our guides.

Vital stats for Spica, also known as Alpha Virgo:

• Brilliance: Magnitude .98 ; as close to magnitude 1 as any star gets; a close double whose combined radiation is the equal of 15,100 Suns.
• Distance: 250 light years
• Spectral Types: B1,B4 Dwarfs
• Position: 13h:25m:12s, -11°:09′:41″

Guideposts reminder

Each month you’re encouraged to learn the new “guidepost” 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. If you have been reading these posts for several months, you may want to relate Spica to two earlier guidepost stars with which it forms a right triangle, Arcturus and Regulus. Here’s what that triangle looks like.

Click image for larger view. (Created, with modifications, from Starry Nights Pro screen shot.)

Click here to download a printer-friendly version of this chart.

Once you have identified the Right Triangle, note carefully the positions of Spica and Regulus. They pretty much mark the “ecliptic.” This is the path followed by the Sun. Also, within about 9 degrees north or south of it, you will find the planets and the Moon. That’s well illustrated in 2012 by the presence of both Saturn and Mars, very near the ecliptic, as noted on our chart.

Arcturus and Regulus are not the only guidepost stars and asterisms in the May sky. Again, if you have been reading these posts for several months, be sure to find the stars and asterisms you found in earlier months. Early on a May evening these will include, from east to west, the following: Arcturus, Spica, Saturn, Leo’s Rump (triangle), The Sickle,  Mars, Regulus, the Beehive, Procyon, Sirius, Pollux, Castor, and in the northwest near the horizon, Capella, and the Kite. Venus will be a bright evening “star” in the west, and if you look early in the month you may catch a glimpse of Sirius and Betelgeuse before they set.

April (2013) events: The changing of the (planetary) Guard and a Comet – still

Ahhh . . . Saturn! We love you – afterall, you brought us Saturn-day! And before I get, you still have a chance to see Comet PanSTARRS in binoculars – mark April 4 on your calendar – though it is growing quite dim.

But let’s start with Saturn In  April 2013 we have Saturn taking over the dominant planet duties from Jupiter – though Jupiter will still be with us even next month, it will get lower and lower in the west, making observing it’s wonderful moons more and more difficult for the binocular user – though next month it will have an interesting naked-eye encounter with a couple other planets.

Saturn, which has been dominating morning skies for months, becomes seriously dominant in the evening sky this month. In fact on April 28th it is at “opposition,” one of those technical terms which is easy to remember because all it means is it will be the “opposite” the Sun in our sky. That is, as the Sun sets in the west, Saturn will rise in the east. But even on the first of April it put in an appearance low in the southeast within a few hours of sunset for a nice triangle of bright “stars” with  Arcturus (our guide star for this month), and the icy, blue Spica.

Click image for a much larger version of this chart. (Prepared from Starry Nights Pro screen shot.)

Click this link for a version of this chart suitable for printing: saturn_rising

Saturn will be just a few magnitudes dimmer than brilliant, zero magnitude, Arcturus and brighter than Spica, though it will be interesting to do a color comparison between these last two. Wait until they’re both pretty high and Saturn should be a creamy yellow, Spica a very definite blue. (Near the horizon they will appear to twinkle madly and flash all sorts of colors due to  our atmosphere. )

Of course Saturn’s main appeal is in the telescope – even the smallest of scopes should reveal it’s beautiful ring system which this month is well placed for observing. (Some times the ring are almost edge-on from our point of view that that is not nearly so much fun. )

Comet Tails

I’m afraid that while you may pick up Comet PanSTARRS in binoculars this month, it will be much easier to follow in a small telescope. I suspect the highlight of the month will come April 4th when the comet, just a matter of a few light minutes from Earth, will appear to pass the Great Andromeda Galaxy (M31) – a whopping 2.5 million light years away.  (Actually, it will be quite close to the galaxy during the entire first week of April.) However, while you should be able to pick up this encounter in binoculars –  both galaxy and comet in the same field of view – it will be a more pleasing sight in a small, low-powered, telescope. Even then, both the comet and the galaxy will be competing with the thick atmosphere, low on the northwestern horizon, not to mention evening twilight.  (Pictures will make both appear brighter because of the sensitivity of long exposures. )

Don’t expect a tail any thing like this long – but you should detect an elongation of the comet in the general direction the tail depicted here is pointing.  M31 should be both bigger and brighter than the comet. Click image for a much larger version of this chart. (Prepared from Starry Nights Pro screen shot.)

Click this link for a version of this chart suitable for printing: comet

As a guide I suggest you wait until an hour after sunset, then scan about 10 degrees (one fist) above the northwestern horizon for the pair. The familiar “W” of Cassiopeia can also help. Use the lower half of this bright asterism as an arrowhead pointing you towards magnitude 2 Mirach.  That will help get you in the right vicinity – not an easy task when you are competing with the twilight. However, even 90 minutes after sunset – when it should be completely dark – this pair will still be more than 6  degrees above the horizon.  Whether you see it or not, I suggest you check Spaceweather.com for the latest photographs because you can be sure some enterprising amateur astronomers will capture the scene.