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Saturday, May 30, 2015

Earthsky Tonight, January 18, 2010: Moon and Jupiter move eastward through the stars

Courtesy of EarthSky
A Clear Voice for Science

Southwest Sky, Moon and Jupiter
Jupiter and the Moon Monday evening

Did you see the moon to the west (or right) of the blazing planet Jupiter yesterday, on Sunday evening? This Monday evening, in contrast, the waxing crescent moon will appear above Jupiter. This is because the moon moves eastward in front of the backdrop stars at about 13 degrees per day. For a measurement reference, your fist at an arm length approximates 10 degrees.

The moon isn’t the only solar sytem body to travel eastward through the stars. All the planets do, including Jupiter. Next to the moon, though, Jupiter travels at a snail’s pace. Presently, the king planet takes about 5 days to move one degree in front of the stars. Meanwhile, the moon moves one degree in just 2 hours.

By the way, the moon’s diameter serves as a great measurement reference. Its diameter spans 1/2 degree.

The sun moves eastward in front of the stars, too, but at about one degree per day. Because the sun is moving faster than Jupiter is, the sun will catch up with Jupiter next month. Day by day, Jupiter is slowly but surely sinking into the sunset. Although the sun/Jupiter conjunction won’t happen until February 28, 2010, this planet will probably be lost in the twilight glare a few weeks before.

Written by Bruce McClure