Good evening, class.

Tonight's observing assignment for Astronomy 212A is to follow the path of the International Space Station across the sky and describe what you see. Please note: There are several opportunities to earn extra credit points!

The easiest way to start this exercise is by locating two planets. Well before 8:50 p.m. on Sunday, Aug. 26, look very low in the west-southwest. The sky will still be illuminated with evening twilight, but you should be able to spot three stars.

The brightest of these is actually the planet Saturn. Seven degrees to its left is the planet Mars, considerably fainter. You should remember from last week's lab that if you hold your fist at arm's length, the width of your fist is about five degrees, so you should be able to easily fit your fist between the two planets.

You can earn two points of extra credit for viewing Saturn through a telescope. If you don't have one, ask your friendly neighborhood amateur astronomer. Be aware that she may be in elementary school, and getting ready for bed.

To check your identifications, look for the star Spica about five degrees below Saturn. Spica is normally midway between Mars and Saturn in brightness, but its very low altitude, only five degrees above the absolute horizon, will make it dimmer than usual.

In fact, the low altitude of all three objects will make this a challenge, and may even place them behind the trees or houses for your viewing location.

8:51 p.m. The ISS may be visible as early as this, though it's not bright at the start of a pass. Look 40 degrees, or four fist-widths, to the right of Saturn, for a star rising in the west-northwest. If you need to set your clocks, go to http://www.time.gov for a precise value, or just type current time into the Google address box for time to the nearest minute.

The Space Station will look like a star moving up and to the left. At first it won't look all that bright, because we're viewing mostly the dark side of the spacecraft. It will also be moving slowly: at this point, it's over a thousand miles away from us, and most of its motion is toward us and difficult to detect, rather than to the side.

But as it approaches us, the ISS will begin to move more quickly across the sky. 8:52. The Station arcs across the bottom of the constellation Botes, the Bear Driver. It just misses the bright star Arcturus in the west.

Read more:

South Jersey Skies: Following the space station