A graceful dance is underway among the heavenly bodies in the southwest, with a peak event visible tonight and tomorrow. The familiar threesome -- Mars, Spica and Saturn -- is about to change sequence as Mars continues its easterly movement. The turning point, now in progress, will be visible from about an hour after sunset until Spica sets close to midnight. Golden Mars appears 1.3 (or 1.4) degrees above bluish Spica. The conjunction (alignment or apparent closeness) of the two can be measured as about one finger width extended at arm's length into the gap.

By Tuesday, the planet will have rounded Virgo's brightest star and, at week's end, the sequence will read, right to left: Spica, Mars, Saturn. A pattern emerges between Saturn and the dim star, Zubenelgenubi, which is below and to the right of the ringed planet, and, further right, Mars with dimmer Spica below and to the right.

Although this week's conjunction of Mars and Spica is a culmination and visual turning point, new, dynamic relationships continue to unfold, although lower in the southwest, for about a month.

This week, for a short time after darkness falls, the constellation Corvus the Crow soars below Spica, close above the southwest horizon, soon to disappear from the evening sky.

A reader of Eyes to the Sky was puzzled about the light coming from stars and planets. She was amazed to embrace the concept that stars are suns, like the sun in our daytime sky. Further, she pondered the notion that planets owe their luminescence to reflected sunlight, as does the moon when seen in our sky.

Another reader conveyed his pleasure at observing the International Space Station, like a moving star, while enjoying the night sky. He sent along the web link for others to look up when the station will be visible at a convenient time and place for viewing. Learn more at spotthestation.nasa.gov/sightings/#.U5SAlXJdVOI

To contact Judy Isacoff, M.A. go to: www.naturesturn.org