STAR TRAK for March 2011

Mercury will make its best evening appearance of the year in March. It will become visible to the unaided eye during the second week of the month about 40 minutes after sunset, almost directly below much brighter Jupiter.

Each night Mercury will be closer to Jupiter, making the smaller planet especially easy to locate. Observers in North America will see the two planets closest together on March 15, about 2 degrees apart with Mercury slightly higher. Around the same time, NASA's MESSENGER spacecraft will begin orbiting Mercury. During the third week, as Jupiter sinks into the sunset, Mercury will continue to appear higher above the western horizon, reaching its greatest separation from the sun on March 22. By month's end it will still set an hour after the sun, but by then it will be hard to locate even with binoculars.

Jupiter will be the only planet visible as the evening sky darkens at the beginning of the month, appearing low in the west. Before month's end, it will have disappeared into the afterglow of sunset.

Jupiter and Saturn are now opposite each other in the sky, each rising when the other sets. At the beginning of March, Saturn will rise more than two hours after sunset and glow bright yellow in the southeast among the stars of the constellation Virgo the Maiden. By month's end it will rise while the sun is setting. Its rings will be tilted 9 degrees to our line of sight. It will be best seen through a telescope when it is highest in the sky, around the middle of the night. Saturn has at least 60 moons, and the largest one, the planet-sized Titan, can be seen with any telescope. Titan will be due north of the planet on the nights of March 8-9 and 24-25, and due south on March 16-17. For the best telescopic views, wait until Saturn is at least a third of the way up the sky, above most of the turbulence near the horizon. See nasa.gov/home/index.cfm" target="_blank">saturn.jpl.nasa.gov/home/index.cfm for the latest news and images from the Cassini spacecraft orbiting Saturn.

Venus will be low in the east-southeast during predawn twilight, a bright "morning star" rising two hours before the sun at the start of the month and 45 minutes later by month's end.

Mars will be lost in the glare of the sun during March.

Equinox

The sun will cross the celestial equator (an extension of Earth's equator onto the sky) on March 20 at 7:21 p.m. EDT (23:21 Universal Time) heading north. This will mark the start of spring in the Northern Hemisphere and fall in the Southern Hemisphere. For the next six months in the Northern Hemisphere, the days will be longer than the nights.

Day and night are not precisely the same length at the time of the equinox. That happens on different dates for different latitudes. At higher latitudes in the Northern Hemisphere, the date of equal day and night occurs before the March equinox. In the Southern Hemisphere, this happens after the March equinox. Information about the exact time of the equinox at different places on Earth's surface is provided at aa.usno.navy.mil/faq/docs/equinoxes.php .

Light pollution

An event called the Globe at Night star count, now in its sixth year, has drawn thousands of participants worldwide. This year's count will run until March 6 (projectdarkskies.org/). The purpose is to get the public excited about what can be seen in the night sky -- but to emphasize that many of these celestial sights are being lost to light pollution.

Moon phases

The moon will be new on March 4, at first quarter on March 12, full on March 19 and at third quarter on March 26.