Courtesy of EarthSky
A Clear Voice for Science
Moon and Jupiter close together on December 20. If your sky is clear, you simply can’t miss the planet Jupiter after sunset. Jupiter will be that blazing point of light to the east (or left) of the waxing crescent moon. Be sure to look for the attractive evening couple at dusk and early evening, because the moon and Jupiter will set beneath your southwestern horizon by mid-evening tonight.
Although the moon and Jupiter appear fairly close together on the sky’s dome, they’re nowhere close together in space. At some 252,000 miles distant, the moon is about 1.35 light-seconds from Earth. But Jupiter resides over 2,000 times farther than the moon, at about 46 light-minutes away.
Neptune, the 8th planet outward from the sun, is only about 1/2 degree (the width of the moon’s diameter) to the upper right of Jupiter. These two worlds align near the same line of sight, but are actually far apart. Neptune lies over 5.5 times farther away than Jupiter, and is more than 10,000 times fainter to the eye. You need an optical aid and a good sky chart to see Neptune.
Tonight’s moon, Jupiter and Neptune reside in front of the rather faint constellation Capricornus the Sea-goat.
Written by Bruce McClure