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February 2005: Vega and Sirius, Comet Machholz & Bad Astronomy



The bright stars Vega and Sirus are almost dead opposite of one another in the starry sky. So when one of these stars is at the verge of setting, the other star is always rising in the opposite direction. For instance, if you live at 40 degrees North latitude or farther north, you should be able to see both these stars at nightfall in early February. With an open sky, you'll see Vega twinkling low in the northwest -- and close to setting -- while the sky's brightest star, Sirius, sparkles wildly in the southeast sky.

As the night turns, Vega sets at early evening while Sirius stays up past midnight. As Sirius sinks toward its setting point in the southwest, look for Vega to rise again in the northeast sky. During early February, at 40 degrees N. latitude, these sparkling gems reappear about-face of each other at about 2:00 in the morning. Keep in mind that Sirius and Vega return to the same place in the sky about four minutes earlier with each passing day, or one-half hour earlier with each passing week.

North of 40 degrees N. latitude, Sirius sets and Vega rises at an earlier hour. In early February, at 50 degrees N. latitude, Sirius lurks to the southwest and Vega lords over the northeast shortly after midnight. But south of 40 degrees N. latitude, Sirius and Vega set and rise at a later hour. In early February, at a latitude of 20 degrees N. latitude, look for Vega to reign in the northeast and Sirius the southwest at about 3:00 a.m. For any latitude, the same rule applies: the stars rise and set four minutes earlier with each passing day.

What's especially amazing about Vega and Sirius is that these two beacons point out the path of our solar system's orbit around the center of the Milky Way Galaxy. To a good approximation, Vega marks the Apex of the Sun's Way -- the direction in which the Sun and its accompanying planets move through space. Sirius, on the other hand, spotlights the approximate position of the Solar Antapex -- the direction from which the Sun is traveling. Looking at Vega, we're peering through the windshield of our solar system; and gazing at Sirius, we looking out our rear window.

For more on the Solar Apex and Antapex, click here, and for some fascinating history on Vega, click here.

Comet Machholz

I'm happy to report that Comet Machholz is still a brilliant fuzzball when viewed through binocuars and is very much a naked eye object on a clear, dark night. Blessed with good seeing conditions on the night of January 28, I saw both Comet Machholz and the Double Cluster of Perseus in the same binocular field.

Throughout February, the comet travels northward toward Polaris, the North Star, and strolls in the region of the sky between Perseus and the North Star. For much of the Northern Hemisphere, Comet Machholz becomes circumpolar, and during the first half of March, the comet lodges quite close to the North Star. Click here for a map.

My eight year old niece, Clara McClure, who was enchanted by Comet Machholz's sublime appearance in the dark skies of Colorado's Sangre de Cristo mountains, has now become an expert of sorts on comets. She has told me, among other things, that the word comet is derived from Greek and Latin and means "long-haired" star.

Bad Astronomy

Phil Plait has made quite a career for himself, dispelling misconceptions on space and astronomy. So it was with great surprise that I read the following on page 55 of Bad Astronomy:

Right now, the Earth's north axis points toward the Sun in June. But due to presession, 13,000 years from now - a half precession cycle - the Earth's north pole will be pointed away from the Sun in June and toward it in December. Seasons will be reversed relative to our current calendar.

The above statement presumes that the Gregorian calendar is based on the stellar year -- and not the seasonal year. The truth is that it's the other way around.

Our current Gregorian calendar makes every effort to align itself with the seasonal year, and does a remarkably good job of it. For the calendar to prove its worth, the Earth's north pole should tilt most toward the Sun on or near June 21 (Northern solstice) as the years go by. As things stand now, the Gregorian calendar is out of step with the seasons by about one day in 3,000 years. Not bad! For the calendar to be accurate 13,000 years from now, the Gregorian calendar would need only a slight tweaking to have the Northern solstice fall on or near June 21.

Presently, the June (Northern) Solstice Sun shines in front of the stars of the constellation Taurus the Bull, only a hairbreadth to the west of the Gemini-Taurus border. Keeping in mind that the Gregorian calendar is a seasonal calendar, we can revise Phil's text to read, "Right now, the Northern solstice Sun resides at the Taurus-Gemini border in June. But due to precession, 13,000 years from now - a half precession cycle - the Northern solstice Sun will be 180 degrees west of the Taurus-Gemini border in June and the Southern solstice Sun will shine at the Taurus-Gemini border in December. Seasons will be reversed relative to Sun's place on the zodiac."

copyright 2005 by Bruce McClure

Cool Planetarium Program!

Your Sky by John Walker

January 2005 Feature * March 2005 Feature