FROM THE UNIVERSITY OF TEXAS McDONALD OBSERVATORY, AS HEARD ON KCBS RADIO WEEKDAYS @ 9:52 A.M., 7:35 P.M. & 2:52 A.M.
STARDATE 7/10/2014: A bright star and a brighter planet are staging a beautiful encounter in the evening sky. They’re quite close together tonight, and will pass even closer over the next few nights. Look for them about a third of the way up the southwestern sky as the last blush of twilight fades away.
The planet Mars is the brighter of the two objects. It shines with a distinctly orange hue — the color of the iron-rich dust that coats much of its surface.
The star Spica is just to the lower left of Mars. It shines white or blue-white — the result of surface temperatures of tens of thousands of degrees for the system’s two bright stars.
Spica is so far away that it remains “fixed” in the same position in our sky — it takes centuries to see any motion at all. But Mars is a close planetary neighbor — the next planet outward from our own Earth — so it moves across the sky fairly quickly. If you plot its position against the background of stars, you can often notice a change from one night to the next.
That’s especially true when Mars is passing a bright star like Spica — you don’t need a telescope or a chart or any other aid to notice its motion across the sky. Mars will move closer to Spica over the next couple of nights, then pass over the top of it on Sunday and Monday. After that, Mars will quickly leave its stationary companion behind — heading toward a couple of other prominent encounters in August. We’ll keep you posted.