What’s up in the sky – for April 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 in the west, the stars of Taurus the Bull are getting lower and lower. If you hold out your hand in front of you, and stretch your fingers, Taurus will be about one and a half “hands” high above the horizon – that’s about 30 degrees. Taurus’ brightest star is Aldebaran, a bright, red giant star about 70 light years away. Its Arabic name means “The Follower” – because the star seems to follow the small cluster of stars you’ll see just to its right, the Pleiades, also known as the Seven Sisters.
To the left of Taurus, you’ll see the stars of Orion the Hunter – most easily recognized by its three closely spaced and equally bright belt stars. Just below the belt, and about one hand high above the horizon, you’ll see a bright whitish star – that is Rigel – an enormous star more than 10 times farther away than Aldebaran, and even brighter. Rigel is about 70 times larger than our Sun, and almost 70,000 times brighter. One day in the far future, it may explode, but even if it did, we wouldn’t know for almost 800 years….
Now let’s look South.
Turn to your left, and look quite a bit higher almost overhead, and you’ll see two bright stars – those are Castor and Pollux, in Gemini, the Twins. The brighter one is Pollux – about 35 light years away. And the dimmer one, a bit higher is Castor. And though you can’t see it, Castor is really a system of 6 stars – three sets of twins! Castor itself is a close double star, with another pair of stars taking about 450 years to orbit about 100 times farther than our planet orbits the sun. And father still is another pair of stars – three sets of twins pirouetting around a common center of gravity, in a celestial ballet that is invisible to our eye
Turn a bit farther to the left, and about ½ way up in the sky you’ll see a yellow-white object – that is the planet Saturn, still in front of the stars of tail of Leo the lion. For now, Saturn is the only planet visible in our evening skies now. Venus now sets before the sun, and Mercury is setting just after sunset. And you’ll have to stay up until 4:30 in the morning before you can spot Jupiter rise in the east!
Now let’s look East, and pick up the brightest star low 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 low in the sky, about one hand above the horizon. That’s Arcturus, the brightest star in the constellation of Bootes, the Herdsman. If you can’t quite spot it from where you are outside now, don’t dismay – by the end of the month, Arcturus will be more than twice as high in the Eastern sky at 9 PM, as our planet Earth zooms around the Sun at more than 67,000 miles per hour…
Now let’s look North.
Turn again to your left, and look for fairly high in the sky – about two outstretched hands above the horizon. Look for a rectangle of bright stars – that’s the cup of the Big Dipper. I’ll pause for a few moments and let you find it!
Looking North in March and April, the Big Dipper is getting higher and higher in our evening skies. Last month we used the top two stars of the Dipper’s cup to find Polaris, the north star. This month, use the handle of the dipper as another guide to find Arcturus. From the cup, move down across three bright stars in the handle, and follow their curving path. You can remember this with the saying, “Arc to Arcturus”. And next month, we’ll be able to complete the saying, as the brightest star of Virgo, Spica comes into view in the eastern skies. Then you’ll be able to arc to Arcturus, and speed on to Spica, too!
Well take a moment now to look around, and just enjoy the stars overhead. For most of us, even the closest star tonight over our head sent its light out more than 8 years ago, only reaching your eyes tonight. And most of the star light you are seeing is tens, or hundreds of years old! Looking at the stars, you are looking back into time. And yet perhaps you are looking into our future, too – that one day we might explore the planets and stars. Tennyson said, “For I dipped into the Future, far as the human eye could see; saw the vision of the world, and all the wonder that would be.” Maybe that could apply to the stars…
That’s it for this month.
Please tune in again next month for the bright stars of May, when we’ll
see more of Spica, and perhaps even the first of the
summer stars, Vega, peeking over the eastern horizon a bit after 9 PM. I’m Scott Hildreth, from
Music this month comes from Saul Stokes, a wonderful innovative composer from the Bay Area. Check out his link in the podcast description. Thanks, Saul!