An interesting line-up appears in the sky the next two evenings. Tonight (8/13/12) and tomorrow (8/14/12) three bright objects—Saturn, Mars, Spica—form a nearly straight line.
Look for this striking sight at nightfall low in the west-southwest. You can easily cover up all three with just your fist held at arm’s length.
Saturn, Mars, and Spica appear close together only because from Earth’s viewpoint they currently happen to lie in roughly the same line of sight. In reality, Mars and Saturn are millions of miles away from each other, and the star Spica is about 260 light years away.
As planets, Mars and Saturn noticeably move over time against the background of stars—Mars, especially. Watch Mars over the next few evenings and you’ll be able to tell it’s trekking eastward relative to Saturn and Spica.
As the Saturn-Mars-Spica configuration continues to change shape, one way to keep track of which object is which is by remembering that stars twinkle, but planets (generally) shine steadily. To tell the two planets apart, remember that Mars is called the Red Planet for a reason—it really does look a bit reddish in the sky—whereas Saturn is more of a pale gold.
On the evening of August 21, the waxing crescent Moon joins this star and planet grouping.