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The Sky This Week, 2012 March 6-13

Planets in the early evening, and Mars at his best.


Jupiter, Venus, & Mercury, 2012 March 4
Imaged from Alexandria, VA
Canon EOS Rebel T2i, 1s @ f/8, ISO 800, 24mm fl
Mercury is just above the top of the pine tree at bottom-center

The Moon brightens the evening and late night sky this week, with Full Moon occurring on the 8th at 4:39 am Eastern Standard Time. This month’s Full Moon goes by many names from many cultures, all of which are symbolic of the changing season: Worm Moon, Crow Moon, Sap Moon, and Crust Moon are the most common examples. Look for Luna to the south of the bright star Regulus in the constellation Leo on the evening of the 6th. On the following night the Moon is 10 degrees south of bright ruddy Mars. Late on the night of the 10th watch the Moon rise in an almost perfect triangle formation with the blue star Spica and the golden glow of Saturn.

Before you retire on the night of the 10th be sure to set your clocks ahead by one hour to begin keeping Daylight Time. Technically this is done at 2:00 am local time on the 11th, when most of us in the U.S. "spring forward". The only people exempt from this ritual are residents of Arizona and Hawai’i who don’t change their time to reflect the changing seasons. The implementation of Daylight Time has roots that date back to Benjamin Franklin, but the concept wasn’t adopted until World War I. It was turned over to individual localities in 1919, re-introduced on a national basis in World War II, and ultimately codified in the law of the land by Congress in 1966. The present rules were amended by the Energy Policy Act of 2005. We’ll stay on Daylight Time until the first Sunday in November, which falls this year on the 4th.

One of the reasons we change our clocks is that this time of the year we experience the most rapid changes in the times of sunrise and sunset. As we approach the equinox we gain about three minutes of daylight per day. During the course of the week sunrise will arrive 10 minutes earlier and sunset will occur 8 minutes later. We now experience some two hours more daylight than we did just three months ago. Spring is definitely almost here!

This will be a banner week to watch the sky during the evening twilight hours. As the week opens the elusive planet Mercury may be found in the west about half an hour after sunset in his best evening apparition of the year. The planet reached elongation from the Sun on the 5th, so he will appear to hover about 10 degrees above the horizon as the sunset glow slowly fades. Early in the week he shines at "zero magnitude" about as bright as all but the brightest star Sirius. He fades by a magnitude during the week as he slowly begins his fall back to solar conjunction on the 21st. Higher up in the sky, you’ll have no trouble spotting Venus and Jupiter. These two planets have been dominating the evening sky since the end of last year, and thanks to Venus’ rapid motion against the stars they are about to undergo a spectacular conjunction. As the week opens the two are about seven degrees apart, with brighter Venus below giant Jupiter. By the end of the week they are only three degrees apart as Venus overtakes her slower rival. Venus will continue to pull away from Jupiter as she climbs higher into the evening sky; Old Jove continues to lose ground to the Sun.

Mars rises at sunset and sets at sunrise as he passes as close to the Earth as he will get this opposition. If you have a small telescope this is the time to take a look at him. His ruddy disc is just under 14 arcseconds in apparent diameter. For comparison, look at Jupiter in the early evening twilight. Jupiter’s disc appears some 2.5 times bigger. Now consider that Mars is about eight times closer to us than Old Jove and you may perhaps have a sense of how big Jupiter is or how small the red planet is. Either way, if you look at Mars between 11:00 pm and midnight you should be able to glimpse his bright north polar ice cap and the dark surface feature known as Syrtis Major. Unlike the ephemeral clouds of Jupiter, this martian feature has been observed continuously since its discovery in 1659. It is a permanent feature on the planet’s surface.

Saturn rises just after 9:00 pm for most of the week, then stalls for an hour thanks to the time-change. By midnight before the 11th he should be well-placed for a glimpse through the telescope, which will reward you with a view of the planet’s amazing rings. Saturn will be with us for most of the spring and summer, though, so you’ll have plenty to look forward to in the warmer months to come.

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