Welcome to You Ask Andy

Jackie Skinner, age 11, of Burnaby, B.C., for the question:

 Do we see the stars as they are now?

This is a thoughtful question. After all, we are told that the distance of the stars is measured in light years. A light year is the distance a ray of light travels in one year. Since light travels at about 186,000 miles a second, a light year tots up to roughly six million, million miles, or six trillion miles. The starlight we see tonight set out towards us many years ago.

This means that we see the stars as they were when their light left them, Some stars are only a few light years away. Others are 20, 30, 100 or many hundreds of light years away, Hence, as far as time goes, we do not get a true picture of the stars at all. We see this one as it was six years ago, that one as it was 100 years ago.

The brightest star we see, and one of the nearest is Sirius, the Dog Star. This fellow, brilliant as a big, sparkling diamond, follows the constellation Orion, the Hunter, over the sky. Bright Sirius is 8.6 light years from our sun. The sparkling dot you see tonight as the Dog Star is really light which set out towards us in the fall of 1949. The starlight which is leaving Sirius at this moment will not be seen by us until late in 1966. Suppose Sirius blew up today. We would not see this tragic event for 8.6 years. That is how long it would take the light to reach us.

Turn from Sirius to the big star Rigel at the foot of Orion. This star is estimated to be 540 light years away. The Rigel we see tonight is really light which started on its way early in the 15th century. If Rigel disappeared from the heavens while Columbus was sailing the ocean, we would not know about it for another 50 years or so.

At the top of Orion is the big star Bellatrix. This fellow is estimated to be 250 light years away. The Bellatrix we see tonight is really a picture which set out towards us early in the 18th century. The bright stars of Orion have formed a constant pattern since before the dawn of history. They form this design only because we see them from a certain angle. Actually, they angle. Actually, they are individual stars separated by vast reaches of space.

Sometimes a violent drama does happen to a star. A nova or supernova is a star which has exploded with an expanding shell of blazing gases. Suddenly a part of the sky is lit up with a new bright star. The event is very rare and the nova and supernova stars on record all occurred far from our part of the sky.

Most of the dramatic novae are several thousands of light years away. The records made of them now are really records of what happened thousands of years in the past. If bright Sirius burst into a nova tonight, our eyes would see no change for over eight and one half years, the time it would take light to bring us the news across the vast reaches of space.

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