By Peter Becker
The Moon will appear to pass very close to Jupiter on the evening of Sunday March 17. The bright white planet will be seen on the upper right and a only a little farther away on the lower left, the bright red-orange star Aldebaran.
The Moon at this time will be a thick crescent, on its way to first quarter phase two days later. Aim your binoculars or a small telescope this way and enjoy the splendid view of lunar craters and mountains jumbled together on the Moon's terminator, the line between sunlight and dark. It will also be a fascinating sight in an eyepiece, to see Jupiter a short distance from our Moon.
Look and see the squat shape of Jupiter, easily seen with even low magnification of about 40X in a small telescope. Inspect the bright dots attending Jupiter; the four largest moons of the planet can even be glimpsed in binoculars if you use a tripod or other solid support.
Compare these bright points with our own Moon. Jupiter's four large moons- Io, Europa, Ganeymede and Callisto, are comparable in size to the Earth's Moon, although with large geologic differences. They appear like stars attending Jupiter because of the vast distance. The Moon is only about 238,000 miles from your backyard- less than some of our odometers have measured. Jupiter and its family of moons are almost 400 million miles away!
Just how close our Moon is to Jupiter depends on where you live. Their separation will vary noticeably from places a thousand miles apart. If you made it a project and arranged with a friend or relative on the other side of the country to take a photograph at the same time, one could compare the shift. Knowing the distance between you and the other person, one could use that with the varying angles between the Moon and Jupiter, to calculate the distance to the Moon. This is known as measuring the parallax.
Viewing the Moon in a small telescope, you may at times see a star very close by. There are of course millions of stars in the background, but most are far too faint to see in a small telescope, and a lot fewer can be seen when obscured by the bright moonlight. While looking at an evening Moon before the full phase, see if there are any stars very close to the darkened edge. Watch for a few minutes to see the star "blink out" as the Moon passes in front. Known as an occultation, the Moon occasionally passes in front of a planet as well, although in this case it is missing Jupiter.
Comet PanSTARRS is still visible, low in the west. Look approximately a half hour after sunset. Binoculars are recommended, to find the comet in the bright twilight. If you look too late when the sky is darker, the comet will have set below the horizon. The comet should appear as a fuzzy star, with a fainter tail rising up from it.
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Keep looking up!