Planets make appearances this month

Posted: Sunday, April 04, 2004

Even though the nights are getting considerably shorter, we'll still have a great planet show going on this month.

Four planets are dominating the evening sky with a fifth barely visible really early in April. In the early evening, look for ultra-bright Venus high in the west.

Then as evening advances, find Orion in the southwest with Sirius, the brightest star, to its lower left, Procyon and Castor and Pollux (the twin stars in Gemini) to its upper left, Taurus with orangy Aldebaran and the star cluster Pleiades above it, as well as Capella in its pentagon of Auriga high in the west.

Watch for Saturn forming a long triangle with Castor and Pollux, now high in the southwest as well. You'll see its rings in a small telescope. Between orange Aldebaran and left next to Venus find another red object of a different kind: Mars.

The accompanying diagram shows the sky at about 10 p.m. Alaska Daylight Savings Time (ADT). All the bright stars and planets just described cluster around the word "Saturn."

The Milky Way runs south to north where, on the northern horizon, you find the bright stars Vega and Deneb. Notice also the W-shaped Cassiopeia inside the Milky Way in the northwest. Next to Cassiopeia is the house of Cepheus, then the Little Dipper and, almost in the middle (in the zenith), the Big Dipper.

Actually, you would want to start with the Big Dipper overhead anyway because its last two stars point to Polaris, the North Star, at the end of the Little Dipper's handle, while the Big Dipper's own handle arcs toward bright and orange Arcturus fairly high in the east.

From there, conclude the journey with Jupiter right beneath Leo. A small telescope will reveal its four large moons and perhaps its cloud bands.

I mentioned some orange and red stars: Arcturus and Aldebaran as well as Betelgeuse in Orion's left shoulder are red super giants and so is Antares in Scorpius, an early fall constellation. Almost all stars appear white to us because the human eye cannot perceive their colors in the blink of an eye, but a long exposure photo picks up colors much better.

It turns out that many stars actually are white, but many others are blue, yellow (guess which), orange and red. Only the brightest-colored stars will exhibit their color to the naked eye.

Notice that a rifle scope may produce too much refraction, making all stars twinkle colorfully, yet these are not the stars' colors.

The above-mentioned four stars should appear definitely red. Rigel in Orion's right foot should appear blue and Capella appears yellow to some people. The colors of stars depend on their surface temperature: blue Rigel at 20,000 degrees Fahrenheit, white Sirius at 17,000 degrees, yellow Sun and Capella at 10,500 degrees, orange Arcturus and Aldebaran at 7,500 degrees and red Antares and Betelgeuse at 6,000 degrees. Since the latter four are huge stars with their stellar atmospheres being a thousand times larger than our Sun's, they also are bright, despite being rather cool.

Andy Veh is an assistant physics professor at Kenai Peninsula College.

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