The Other Stars That Move; Satellites

You may have noticed a very bright star in the western sky these past few weeks, rising slowly and growing brighter. This is the planet Venus, Earth's near twin, and the hottest planet in the Solar System. It will continue rising until it reaches its maximum altitude (or eastern elongation) on the 20th of August. That it's bright goes without saying; its heavy cloud cover reflects most of the visible light that reaches it back into space, and therefore towards us.

Again, it is bright, and will simply grow brighter.
However, there are objects that cross the sky that can be, momentarily, as bright. These are satellites. It so happens that May is a great time to watch for them.
So, just how many satellites are up there, and how many are visible?
The number of satellites that are up there is in the thousands, ranging from a few centimeters or less to the size of locomotives, and one even larger. They look like moving stars; they can be distinguished from aircraft because they are normally just a single point of light. The light they reflect is not always constant, though. As satellites age and go dead, they frequently lose control and begin spinning. When they do this, they appear to pulsate depending upon the speed of their rotation. A few satellites flare up significantly, easily brighter than Venus.
The best time to observe satellites is just after sunset. Satellites can be seen moving either generally from the west to east or due north or south (polar orbits). By the way, be sure to wave at the ones in polar orbits, as many of those are reconnaissance or earth observation satellites, blistering with cameras!
The largest satellite currently in orbit is the International Space Station, the ISS. This orbiting platform covers the area of a football field and has enormous photovoltaic panels (solar panels). There are normally three people on board at any one time; this jumps when a space shuttle is docked.

The ISS in its current configuration. Image courtesy NASA

What does the ISS look like as it passes overhead?
It is brilliant. Its brilliance is already much brighter than Venus, as it slowly follows its arch across the sky. On the 13th of May, it will make a pass through our northern skies here in northeast Florida, rising in the northwest, though much later than most satellites; it will clear the horizon at 10:19pm. The pass will only last three minutes, rising just 15 degrees above the horizon, but if you have a clear shot north, you should be able to see what looks quite a bit like the planet Venus, moving up, growing brighter, then fading through yellow, orange and red as it vanishes into the night.

ISS pass on the 13th of May, 2010. Chart courtesy Heavens-Above.com

The following day, the 14th, space shuttle Atlantis is scheduled to go aloft to the ISS. Try to catch the ISS before the shuttle does!

The Planet & The Bees

For the past few months, the planet Mars has been shining its orange-ish glow furiously in the winter sky, for a time even out-shining the brightest stars. As the months have rolled along, it has begun to dim a bit as the distance between Earth and Mars grows. That doesn't mean that Mars is simply going to fade away; it will still be plenty bright, and it has a rendezvous with a wonderful deep sky object this month. That deep sky object is M44, the Praesepe or Beehive Cluster.

When I say rendezvous, I mean appearing to be very close to. In actuality, there are a few hundred light years between Mars and the Beehive; M44 is 577 light years away.

Mars and M44 on the 13th & 14th of April

The Beehive is an open cluster, a little over a thousand stars gravitationally bound together and sharing a common origin. Most of the stars that compose the cluster are small red dwarfs, too faint to be seen with most telescopes. The ones we do see are much larger and brighter, and, in fact, there are a few giants within the cluster itself. Like most open clusters, the largest members seem to be huddled within the interior, with the fainter stars spreading out from there. It's this arrangement that gives the Beehive Cluster its name, for it really does resemble a swarm of bees buzzing around a hive.

Normally, in urban and suburban skies, the Beehive is a little difficult to locate, due to light pollution. If you do live under such conditions, your best tool for seeing them is either a pair of binoculars or a small telescope. Once it is located, though, the brighter stars immediately show up, and a few more also pop into view with patience. The problem is that the Beehive lies within the somewhat faint constellation of Cancer, so locating it might be difficult. On the nights between the 13th and 16^th of April, 2010, Mars will make finding the cluster much easier, for on its closest approach (16^th April) it will lie 1° 10' north of the cluster. That's approximately two lunar (Moon) diameters. Just find Mars, and head a little way south.

Mars & M44 on the 16th of April

If you live in a more rural region, though, you'll see Mars close to a smudge of light, the condensed light of hundreds of stars that sent their photons in our direction almost fifty years before Columbus set out on his voyage of discovery. Whether you live under urban, suburban or rural skies, be sure to enjoy your voyage of discovery as you get a look at this little gathering of the Planet and the Bees.

When Worlds Appear To Get Real Close

Spend a few minutes outside this evening and take a look to the west just after sunset. You'll see two stars up there in the sky glow. They're not stars, they're planets; Venus and Mercury. And Mercury will not be around for long.
Mercury takes 88 days to go around the Sun; that's about three months. When it reaches its highest point in the western sky (known as its maximum eastern elongation, basically its furthest point east), it doesn't stay long, and begins its dive right back into the sunset. Meantime, Venus takes a leisurely 225 days to orbit the Sun (though, compared to our 365 days, leisurely might not be an appropriate term, but compared to Mercury...). This trip round, Mercury didn't climb quite as high as Venus (it actually reached its peak on the 8th of April).
It's their proximity to one another in the evening sky that probably piqued the interests of astrologers of old; surely, they must have something going on (goddess of beauty seeing the heavenly messenger? Isn't that like having a fling with your postman?). The truth is that they are tens of millions of miles apart, with Venus still climbing to its maximum eastern elongation, which is months away (more next week).


In early July, Mercury will repeat a climb into the west, a good time for it to be caught for sure. If you're a morning person (I am, with the right amount of coffee), you can catch Mercury in early to mid May doing the same thing in the morning sky. Meantime, enjoy catching these two hotties (well, because they are pretty darned hot) as they hang out together in the sunset.

(This post written on a laptop running Xubuntu. Star chart edited from KStars, Solar System chart co-opted from "The Solar System Live" at Fourmilab.ch)