Michael R. Veall, age 13, of Niagara Falls, Ontario, Canada, for his question:
Which is the largest known star?
In this question, the word 'known" makes all the difference. It proves that a young space age student knows that even our best astrophysi¬cists do not know all there is to know about the starry heavens. They cannot describe the largest star but merely the largest star they have been able to measure.
Stars are always fooling us and playing tricks on our eyes. Maybe that explains why they twinkle so merrily though this is not likely. They are, of course, so very far away and distance always distorts the true picture. Measuring stars is a tedious task for trained experts using super fine instruments. First they must know a star's distance. They figure this from the parallax angle at the top of an immense celestial triangle. This requires taking a detailed telescopic photograph and com¬paring it with another one taken six months later. Knowing its distance, plus several other facts, enables experts to estimate the true size of a remote star.
Even with all these modern skills, people evmetimes go wrong. For example, you may hear tell of a super giant star in the constellation Hercules. It is supposed to be about 3,000 times wider than our sun. This fellow actually is two large stars, quite close together and surrounded by one huge globular cloud of gases. If this were one star, it would indeed be the largest one we know, but since it is two stars, it is hardly fair to count it.
Many of the bright stars are pairs that orbit around each other, but experts can distinguish one from the other. The star with the largest reli¬able measurements happens to be one of a pair of these celestial twins. The two form a double or variable star. Periodically the smaller one is eclipsed by its huge companion, and the duration of this eclipse, along with distance information, has enabled astronomers to calculate its enormous size.
The whopper's official name is Epsilon Aurigae. "Aurigae" means that it appears in the constellation Auriga, the Charioteer. The diameter of Epsilon Aurigae is estimated to be about 2,000 times that of our sun. If we used it as a replacement for our sun, it would engulf Mercury and Venus, the earth and Mars and Jupiter. Its outer edges would reach out beyond the orbit of Saturn and about halfway toward the orbit of Uranus. Several stars waiting for accurate measurements may be still bigger and we may never be able to say for certain that we have found the biggest star in the universe.
The constellation Auriga appears in our winter skies. You surely know Aldebaran, the bright glowering eye in Taurus, the Bull. A.,uriga is a tent shaped group of stars a little to the north of Aldebaran. One of its bright stars is Capella, alias the Goat, which is really a triple star. With the help of a small telescope, several dazzling star clusters can be spotted in Auriga, but the greatest star we have yet found does not shine with enough brilliance to make it easily visible.
Heather Stewart, age 10, of Ottawa, Ontario, Canada, for her question:
What is meant by nomads?
The word "nomad" is borrowed from an older word that meant pasture and grassy meadows. It also happens to be related to our word "nimble"¬which means able to move around in a sprightly fashion. We refer to cer¬tain peoples as nomads because they are always on the move from one place to the next. Very often their movable way of life happens to be related to green, grassy pastures. Many nomad people make their living from flocks of sheep, goats or different types of cattle. These creatures, of course, are grass eating grazers. In the wilds, nature provides these crops in differ¬ent locations with the changing seasons.
In.mountainous regions, nomad shepherds lead their flocks down into the sheltered valleys. In summer they lead them high up the slopes. Our early ancestors were wandering nomads. They were always moving from place to place, seeking game and fodder, and they had no permanent place to call home. Many people still live nomad lives, toting their movable tents and possessions. Home to them is any place, any place at all where they stop long enough to set up their camps.