Where is the South Star?

Thursday, March 28, 2013

OK space fans, let's go to the mailbag for this week's question. "What is the brightest star in the sky?"

Okay, good one.

I have heard some who have said that Polaris, the North Star, is the brightest star in the sky; too bad they are wrong. In fact, there are about 50 stars in the sky that are brighter than Polaris.

With all the attention paid to it, the average citizen might think that Polaris, would be the brightest, but such is not the case.

First, to answer the question, then to say why.

The brightest star visible in the sky -- northern or southern hemisphere -- is Sirius, in the constellation Canis Major, The Big Dog.

It can be located a little west of due south about half way up the sky an hour after local sunset. Canis Major is just to the left of our old friend, Orion, the Hunter.

The reason Sirius appears so bright is its location. It is a little more than 81⁄2 years from Earth. You will recall that a light year is the distance light takes to travel in a year at the speed of 186,000 miles per second.

In case your calculator doesn't have enough zeros for that, it is about six trillion miles. Then you multiply that by eight. Or not, wouldn't want your calculator to blow a diode.

Polaris is the North Star because it just happens to be the closest star to where Earth's north axis is pointing. In 14,000 years Vega in Lyra, the Harp will be the North Star.

Just for your information, there is no "South Star."

This is due to a process called precession.

As Earth spins on its axis, it wobbles, sort of like when a child's top is slowing down and losing momentum -- not that Earth's spin is slowing, it is just an illustration.

This spinning wobble moves where the axis points about one degree every 72 years and proscribes a circle on the sky pointing at different stars at different times; this spinning wobble takes 26,000 years to complete one complete circle.

This wobble also moves something else, the point where the sun crosses the celestial equator, the equinoxes. That is why it is also called the precession of the equinoxes.

In 2,000 B.C., the vernal equinox, the first day of spring, the traditional day when the year started, was in the constellation Aries, the Ram.

Now, 4,000 years later, it has moved 11⁄2 constellations west to a point halfway between Pisces and Aquarius.

Now for those of you who follow astrology -- just so you will know and not that it will put a knot in your knickers -- but right now, in March, the sun is not in Aries, it is at a point half way between Pisces and Aquarius.

So, for all of you born in March, and thought you were an Aries, you are not. If anything, you are a Pisces; of course if that means anything.

SKY WATCH: Full moon, yesterday, March 27. Tonight and Friday the moon will bracket the planet Saturn. On Thursday it will be up and right of the planet and on Friday it will be below and left. The moon, being full, may wash out the sky, so binoculars will help.

NEXT WEEK: More astronomical blather.

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