What’s up in the sky – for May 2009
Welcome to the podcast.
I’m Scott Hildreth, astronomy professor at
The best way to use this podcast would be to download it to your favorite MP3 player, and go outside any clear night this month, about 9 O’clock in the evening, as far away from street lights or other illumination as you can get. You don’t need a telescope – we’ll just explore with our eyes together, and see what we can see! So if you aren’t already outside, pause this podcast now, grab a friend, and join me … for the stars!
So let’s get started! As always, we’ll begin by looking west, in the general direction that the sun set.
This month we say good bye to the stars of Orion, which will be setting early in May, not to return until late Autumn. Early in the month, about 9 PM, looking west you’ll still see the stars of Sirius in Canis Major, the belt stars of Orion, and the bright red eye of Taurus, the star Aldebaran, all about the same height – perhaps one hand above the horizon. But by the end of the month, with the sky brighter and brighter as we head toward summer, you’ll not be able to see these stellar beacons that usually grace our winter skies…
The two stars you can see, about two hands high above the
horizon in the west, are Procyon, on the left – in the constellation of Canis Minor, and Capella, on the right, in the constellation of Auriga, the charioteer.
Procyon is a wonderful close star, only about
11 light years away, and bright more because it is
close, like a next door neighbor shining a flashlight your way. But its name heralds its importance, from the
greek, with Pro meaning
“before” and “Cyon” meaning dog. Because it rises
before Sirius, the much brighter star in Canis Major,
and it was Sirius’ rising in the early August mornings that foretold the
flooding of the
To Procyon’s right, Capella shines from almost 4 times further away, the combined light of two very bright stars dancing around each other in just over 100 days, as close as Venus is to our sun. One of these two tightly-embracing stars is about 90 times brighter than our Sun, and the other about 60 times brighter, and together they make up an apparent star ranked as the fourth brightest in our Northern sky.
Now let’s look South.
Turn to your left, and look even higher – about 3 hands held in front of you, with fingers outstreteched. The brightest object you can see is still our ringed neighbor Saturn, some 800 million miles away, in front of the constellation of Leo. Above and to the right of Saturn lies Leo’s brightest star, Regulus, meaning the “little king” or the “king’s star” – one of only a few with Latin names in the sky. If you had a telescope capable of seeing the 80 light years or so to Regulus, and magnifying that star, you’d find it odd indeed. From its light, we know Regulus is spinning very fast, about 50 times faster than our Sun, and so fast that it would look more like an egg than an orange. And that’s not all - like many stars in our sky, Regulus is not a single object, but actually a system of two pairs of stars. Regulus itself has a nearby tiny companion orbiting about the distance of Mercury from our sun, and another pair orbiting much, much farther away – perhaps 100 times the average distance of Pluto. While the inner star orbits Regulus in about 40 days, the outer pair take more than 120,000 years to make one trip… Wow.
Now let’s look East, and pick up two of the brightest stars in our Spring Sky.
Turn to your left once again, so that you are now facing in the opposite direction from where you were looking when we started. Look about half-way up in the sky, about two hands above the horizon. That’s Arcturus, “the Bear-Watcher,” the brightest star in the constellation of Bootes, the Herdsman. And as we learned last month, a nice way to spot Arcturus is to use the curved handle of the Big Dipper, which you can spot high in the Northeastern sky, to “arc to Arcturus.”
Arcturus is about 37 light years away, and while cooler than our Sun (which explains its orange tinge), it is much larger and much brighter than our star – more than 200 times brighter. Arcturus represents what happens to stars like our sun when they age, and their internal energy source changes from fusing hydrogen to fusing helium.
A bit below and to the right of Arcturus lies Spica, in Virgo the Maiden. Spica will be whiter, and dimmer, and lower than Arcturus – and a bit more “underneath” the constellation of Leo. Spica is yet another multiple star, and in this case, an extraordinarily hot and bright pair of stars that spin dizzily around one another in under 4 days, tugging so hard on one another with their gravity that they bulge outwards noticeably. And around them orbit yet more stars. You are looking at a stellar tango 260 light years away when you gaze on Spica.
Now let’s finish our May tour looking North.
Turn again to your left, and look for fairly high in the sky – about three outstretched hands above the horizon. You should be able to spot the Big Dipper, now almost “upside down” in our northern skies, as if it was emptying its dipper down on top of Polaris. Remember to use the two stars of the Big Dipper’s cup – on the opposite side of the handle – to point to Polaris.
Well take a moment now to look around, and just enjoy the stars overhead. As you’ve heard tonight, many of the apparently single points of light over our heads are in reality members of multiple star systems, often as closely spaced pairs of stars, or pairs orbiting still other pairs. Some race quickly around their partners, and others orbit in more stately and slow dances. We know now that most of the stars we see are not single entities, like our sun. But we are also learning that many of the single stars we do know of have planets, too. Will it be long before we learn of Earth-like planets orbiting other stars at the right distance for liquid water to exist? Wonderful, wonderful stuff to think about, as the stars whirl above our heads….
That’s it for this month.
Please tune in again next month for the bright stars of June, when we’ll
learn more about Spica, and the first of the summer triangle
stars, Vega, peeking over the eastern horizon a bit after 9 PM. I’m Scott Hildreth, from