Page:The Music of the Spheres.djvu/154

 Perseus (three bright stars dangling below the Big W) and may be sighted in a straight line from the top of the bowl of the Big Dipper. In the early evening on February 5th it lies exactly on the meridian halfway between Orion and the North Star, while in August it is low in the northeast and in June low in the northwest.

The spectroscope has shown that Capella really consists of two great suns of nearly equal brilliance. These two stars lie so close together that there is not much more than half the distance between our earth and sun between them,—and they revolve around this common center of gravity in only 104.2 days! As they revolve around this point the lines in the spectroscope periodically split, thus proving the double nature of the star. In the present state of our knowledge about eight stars out of twenty are binaries or multiples.

Short as seems the period of revolution of Capella and its companion compared to Sirius and its companion, which is about 50 years, or the couple of couples composing Castor, which is about 900 years, there are stars so close that they complete a revolution in a few hours. The very atmospheres of one pair of suns, δ Cephei, perhaps intertwine like lovers' arms, for they whirl about their common center of gravity in only 4½ hours!

The distance of Capella from the earth has been estimated as being about 34 light years. A light year is the distance that light would travel in one year at the rate of 186,000 miles a second. This is about six million million miles! Thus the twin suns in the system of Capella could have rolled off their tracks and exploded into atoms 29 years ago and yet we would know nothing of this catastrophe for 5 years to come.

The fact that light takes a certain amount of time to travel and is not instantaneous, was first discovered by watching the little