by Robert Victor
All-sky evening star charts and sky calendars for March and April 2011, illustrating events mentioned in this article, such as the moon passing planets and bright stars, and the Mercury-Jupiter pairing low in the west at dusk around March 15, can be found on the web at www.pa.msu.edu/abrams/ABDNHAMar-AprSkies/.
Follow the Moon!
The moon’s orbit stands nearly vertical in the sky soon after sunset each year in late winter/early spring for observers at mid-northern latitudes. In 2011, dates to follow the moon’s progress at dusk from thin crescent to Full are March 6-19 and April 4-17. On the first evening of each interval, the moon is not far above the horizon and the very thin crescent may be difficult to spot, especially if you have mountains to your west. Challenge your students to observe the young very thin crescent moon on Saturday, March 5, within 30 hours after new. About 25 minutes after sunset, the crescent sliver will be just 7 degrees up in the west and 13 degrees lower right of Jupiter. Notice its horns, pointing away from the sun, are pointing straight up!
For the next week, the moon climbs much higher each evening as it passes the bright stars of the zodiac. Encourage your students to face west about half an hour after sunset on Sunday March 6. Those who do so will be rewarded by the sight of a beautiful crescent moon not far to the right of Jupiter. On that date and on the next few evenings, as the sky darkens, alert your students to look for the faint bluish glow of earthshine on the moon’s dark, non-sunlit side.
By the latter half of the week of March 6-12, students may also begin to notice the planet Mercury a few degrees to the lower right of bright Jupiter. On each successive evening, Jupiter appears lower, owing to Earth’s faster revolution around the sun, and Mercury appears higher, owing to the innermost planet’s even faster revolution, until on March 15, the two planets appear to pass each other. That evening, some 45 minutes after sunset, Mercury and Jupiter are just two degrees apart, with fainter Mercury to the right of Jupiter. This will be the best conjunction, or pairing, of bright planets in the evening sky this year! (more…)