If you can find a spot with a completely unobstructed eastern horizon, you can watch an extraordinary sky show from late April 2011 through the end of May. Every morning just before sunrise, four planets combine to form fascinating and ever-changing patterns. This is the tightest grouping of bright planets that has occurred yet in the 21st century.If you live in the Southern Hemisphere, you can watch the whole show with your unaided eyes, but you will need binoculars to appreciate it properly from mid-northern latitudes. Go outside 45 minutes before sunrise and scan the eastern horizon until you find a planet. You're sure to spot either Venus or Jupiter first, because these are by far the brightest of the four.
Venus appears at just about the same spot every morning in May — just 2° or 3° above the horizon 45 minutes before sunrise for observers at mid-northern latitudes, and rising 3° higher each 15 minutes after that. If you pay attention to its location, you can probably continue to see it without optical aid long after the Sun rises.
Jupiter is very low at the beginning of May, but it passes Venus on May 11th and ends the month more than 12° above the horizon 45 minutes before sunrise. So by mid-May, you're likely to spot Jupiter before Venus despite the fact that it's less than one-quarter as bright.
Mercury is the 3rd-brightest planet in the grouping, but it's five to ten times fainter than Jupiter, and quite low in the sky. So you're likely to need binoculars to spot it. It tracks Venus's motion, staying a few degrees to the lower left of the brighter planet throughout this period.
Mars is quite faint, just one-hundredth as bright as Venus. It starts May very low in the sky, but catches up with the Venus-Mercury pairing around mid-month.
A thin crescent Moon joins the show from April 29th to May 2nd and again on May 29-31.
Click here to view a 700-Kb movie of the four-planet dance. After watching the general progression, step forward and back to see the configuration on any particular morning. You may need to install QuickTime to watch the film if you haven't already done so.