What’s up in the sky – for June 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 portable MP3 player, and go outside any clear night this month, about 10 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, and grab a friend, and join me … for the stars!
Remember if you are listening outside later in the month, the stars in the East will be a little bit higher, and those in the west a bit lower than I describe. But you can visit the podcast website for star maps and interesting links to information about the stars, and the music you hear!
So let’s get started! As always, we’ll begin by looking west, in the general direction that the sun set, but we have to start our observing a bit later in the evening, as we head towards the summer solstice, which will occur on the twenty-first of this month.
After sunset, the brightest stars you’ll be seeing in the west about 1-2 outstretched hands above the horizon are in the constellation of Leo –along with the planet Saturn, still the brightest object in our western skies after sunset, about one and one-half hands high early in the month.
Last month we talked about Leo’s brightest star Regulus, which you’ll see below and to the right of Saturn. This month look now a bit higher, perhaps just three more “fingers”, and to the right of Regulus - you’ll see a bright star named “Algieba”, the mane of the lion. It’s a double star whose two partners are both old – as stars go – and swollen into giants much bigger and brighter than our sun. Taking almost 130 years to dance one another, alternately close and far away, swooping in to a bit farther than Saturn’s orbit from our Sun, and then out to about 5 times the distance of Pluto.
With the solstice occurring this month though, you’ll find the western sky stays light very late, and it’s not going to be easy to see more stars in the west, so let’s turn away to darker skies to see more stars!
Now let’s look South.
Turn to your left, and looking about two hands high above the horizon, the brightest star you’ll see should be Virgo’s Spica. An amazing combination of multiple stars, Spica shines with more than 2100 times the light energy our sun emits, and its brightest member is most likely massive enough to supernova one day in the far, far future – a celestial firework we wouldn’t spy until about 260 years after that stupendous event, given the system’s distance. And above Spica in the south, about 3 hands held outstretched at arms length, and almost over your head, lies Arcturus in Bootes.
Look now closer to the horizon, just one hand high, and perhaps two hands to the left of Spica, and you should see gleaming in our early summer skies the wonderful star Antares, the brightest of the constellation Scorpius.
Antares’s name is Greek, and refers to the star’s similar color to the planet Mars, which shines with a very red hue, and like the other planets in our solar system, is always seen near the plane of the solar system, which is seen to stretch across our sky in an arc called the ecliptic just above Scorpius. Antares, too, is near that ecliptic, and as red supergiant (and physically one of the biggest stars in the sky), looks red, just like Mars. And so you can see the roots of that star’s name – it looks like Mars, and is near where Mars might be in the sky – but it isn’t Mars! We’ll see much more of Antares as it climbs a bit higher in the southern summer skies, and share more of its amazing characteristics next month.
Now let’s look East, and pick up the rising summer triangle, with its three bright stars in three different constellations
Turn to your left once again, so that you are now facing in
the opposite direction from where you were looking when we started. The
brightest star you can looking East, about one and a half-hands high over the
horizon, is Vega, in the
constellation of Lyra, the Lyre. To its left, and a bit closer to the horizon
(about one hand high) is Deneb, in Cygnus the Swan.
And to Vega’s right, and much farther below, is Altair, in
Of the three Vega is a young, hot star, just a bit over 25 light years away. It is at least twice as massive as the Sun, and fusing its hydrogen fuel much faster, so in fact that it should shine as a “normal” star perhaps just 1/10th as long as our sun. And we know Vega is surrounded by a disk of dust – perhaps the raw material that would form into planets if the star would last long enough.
Deneb – below and to the left - is almost 60 times farther away than Vega, perhaps 1500 light years away – and to be as bright as it is from so great a distance, it is truly a supergiant among stars. Big enough to stretch from our Sun almost 90 million miles into space (to our orbit!), Deneb is more than 60,000 times brighter than our star
Altair, lowest right now in the Eastern sky, is the nearest, and relatively coolest of the three stars – about 17 light years away and just a bit under 11 times brighter than our Sun. And like Vega, Altair spins very fast indeed – more than 100 times faster than our sun. Where sunspots on the sun we see take about a month to rotate over its surface, they would take less than ½ day on Altair to zip around.
Now let’s finish our June tour looking North.
Turn again to your left, and look fairly high in the sky – you should spot the big dipper about 3 hands high over the horizon when held at arm’s length. If you’ve remembered how to use the Dippers’ two brightest stars in its cup to point to Polaris, you’ll see our North star about 2 hands high as well. Tonight, look just above Polaris, and see if you can spot two somewhat bright stars about four more “fingers” higher in the sky. Those are Kochab, on the left, and Pherkad, on the right – known as the “guardians of the pole” because of their constant position around Polaris. Kochab is about 125 light years away, a swollen orange giant star more than 500 times brighter than our sun. And Pherkad is about 4 times further away, and at least twice as bright as its apparent partner – making it appear to our eye about the same relative brightness. And it, too, is a swollen giant star, as are so many that we can see above us.
Though it might not seem so, all these massive giant stars are relatively rare in the stellar freeways of the Milky Way. Like formula 1 racing cars, or the very occasional Ferrari that we might see, they are outnumbered a million to one by more normal sun-like stars. But the giants like Pherkad and Kochab, Deneb, Antares and Algieba shine so brightly that across the vast emptiness of space, they are the easiest to spot.
Look East once more towards Deneb – it’s one of the farthest stars you’ll see, and imagine in the volume of space between our Sun and that star lie perhaps 30 million other stars. Most are much, much smaller and dimmer – more like Honda Civics, that get much better gas mileage, and as stars, will shine for billions of years longer. But those occasional gems of bright stars certainly make the sky interesting!
That’s it for this month.
Please tune in again next month for the bright stars of July, when we’ll
learn more about Antares and the other stars of Scorpius, which you’ll be able to spot in our summer skies. And remember July 4 will be the day our
planet is furthest from the sun in its yearly orbit – that’s right *farthest*
from the sun! Curious? Listen in.
I’m Scott Hildreth, from
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