For bright stars, look to the south

The Sky Guy

Posted: Sunday, March 19, 2006

Since the winter sky appears now in all its splendor, I just included the most interesting and beautiful part of it in the graphic — all those bright stars in the south — instead of the entire sky as I usually do.

There is the hunter Orion with its belt, sword and the bright stars Betelgeuse and Rigel. By themselves are Sirius and Procyon in the Big Dog and Little Dog, respectively, forming a nice straight line with Saturn which is to the right of the Beehive cluster. The twins, Gemini, are marked by Castor and Pollux. The pentagon of the charioteer Auriga with bright star Capella appears highest, and the bull Taurus with Aldebaran and the cluster of the Pleiades hosts Mars.

As for the planets, at midnight Jupiter rises in the east and becomes prominent in the low southeastern sky during the rest of the night. Venus rises just ahead of our sun but it’s so low in the sky that you have to scan the southeastern horizon carefully during dawn to see it.

A total solar eclipse will visit northern Africa, Turkey and central Asia on March 29. Europe, the rest of Africa and most of Asia will see a partial eclipse. Every few years a prominent eclipse can be seen somewhere in the world. In 1991 an eclipse was visible in Hawaii and Mexico, in 1999 Europe, this year in Northern Africa and in 2009 one will be visible in China. Although there are two solar eclipses every year, many of them are only partial ones or are visible in inaccessible places, like the 2008 eclipse seen in Antarctica. A solar eclipse is accompanied by a lunar eclipse, in this case two weeks prior on March 14, on the same continents of Africa, Europe and Asia.

A friend of mine told me of an office discussion she had about whether winter days and nights in Barrow are completely dark. I haven’t been in Barrow in the winter so I can’t answer that first hand. But some astronomical knowledge does supply the answer. For one, since our sun is close beneath the southern horizon during midday, I imagine that the sky looks like dawn or dusk for a few hours.

Then there’s our moon in the sky, depending on its position in its orbit. The sun and moon, as well as planets and asteroids, move along or at least very close to a path called an ecliptic, a circle that stretches across the sky through the Zodiac constellations. The moon, planets and asteroids do that while in the case of our sun it’s actually us, Earth, that is orbiting, but from our vantage point it seems that our sun is the orbiting body. That’s the necessary vantage point used in this discussion.

Our sun sweeps through these constellations once per year — relatively slowly. Since Taurus, Gemini and Cancer are Zodiac constellations that appear quite high in the sky in the northern hemisphere and our sun moves through them between May and August and becomes circumpolar, meaning it never sets, that’s when we have summer. Scorpius, Sagittarius and Capricornus are really low in the sky and that’s where our sun is from November to February, so therefore it barely rises above the horizon and we have winter at that time.

Our moon on the other hand moves through these constellations once a month — relatively fast. So once per month it’s very high in the sky and circumpolar in Barrow for a few days and every month it’s below the horizon all day and night for a few days. For example, during most of December our sun is in Scorpius and thus never rises. But when our moon is in Taurus, as it was in mid-December, it is circumpolar and very high in the sky. Since Taurus is in the opposite part of the sky from Scorpius, our moon also was full at that time and Barrow must have had beautiful circumpolar full moon nights and “days” during mid-months this past winter.

Andy Veh is the physics and astronomy instructor at Kenai Peninsula College. He can be reached at aveh@uaa.alaska.edu.



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