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Up in the Air

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Get binoculars ready for September star cluster

By Daniel B. Caton
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The best celestial views right now are at the beginning and end of the night. The only bright planets visible bookend our night with Venus and Saturn low in the west at dusk and Mars and Jupiter low in the east at dawn. Late evening is marked by the summer Milky Way stretching across the sky from north to south with its dark areas of interstellar dust.

Sept. 8-10, Mars crosses the Beehive star cluster in the constellation of Cancer. It will be low in the dawn sky as it does it – only 20 degrees above the horizon just before dawn. That’s two fist-widths at arm’s length, if you want to determine whether your east horizon will justify setting your alarm clock!

The star cluster is about a degree and a half in diameter – that’s three times the angular size of the moon. The best thing to see it with is a pair of binoculars. When it’s high in the evening sky in spring, you can see it with the naked eye as a small fuzzy patch of light. Galileo was the first to turn a telescope toward it, resolving it into a few dozen stars visible in small scopes.

Of course, the stars are immensely farther away than Mars, just providing a backdrop for the near planet. The Beehive is a group of stars born together and bound together, and is about 577 light years from us. The starlight you see left the stars in the year 1436, a century before the birth of modern astronomy. The light you see from Mars left that planet about 19 minutes ago.

The cluster fits nicely in a pair of binoculars but its actual size is about 80 light years across. The group was born about 600 million years ago, just when multi-cellular life was evolving in Earth’s oceans.

A nearer and more subtle astronomical target is visible in dark pre-dawn skies in early September and October – a time this fall when the moon is not too bright. That is the zodiacal light, a faint triangular glow of light that extends above the east horizon along the zodiac.

This light is from dust in our solar system, most likely dust from short-period comets that orbit the sun with periods of less than a couple of centuries. Interstellar space was suggested as a dust source in the Ph.D. dissertation of Brian May, astrophysicist and guitarist of the band Queen. However, the dust theory is difficult to prove.

Whatever the source of it, you will need skies free of light pollution to see the Milky Way or the zodiacal light. But, Mars in the Beehive will be visible to anyone with binoculars, so take a look if you can!

Daniel B. Caton is a physics and astronomy professor and director of observatories at Appalachian State University. Email: catondb@appstate.edu. More on this month’s column: www.upintheair.info.

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