Stormy Sun

Most stars are too faint to suit astronomers, but the sun is too bright. Astronomers have been able to analyze the sun's light and photograph the spots that cruise in mysterious cycles across its face. But until recently, their observations have been limited mostly to the brilliant surface itself. Except during total eclipses, the details of the sun's atmosphere have been lost in its glare.

In a new book, Our Sun (Blakiston; $4.50), Dr. Donald H. Menzel of Harvard tells how new and refined instruments have opened the sun to astronomers' prying eyes. There is plenty of action to watch, for the sun is a vast turmoil of violent storms and convulsions.

White Worms. One instrument, the spectroheliograph, takes pictures of the sun in the light that comes from single elements, such as hydrogen or calcium. The instrument has recently been improved to the point where it can take motion pictures (spectroheliokinemato-grams) which show the sun covered with patches, streaks and mottlings, most of them in motion. The pattern of the mottled background often changes completely in 15 minutes. "Motion pictures of the surface," says Dr. Menzel, "present a sort of 'crawly' appearance--like white worms in a pile of carrion."

Some of the photographs show that the sun, though completely gaseous, has mountains--vast mounds of luminous gas as much as 100 miles high. The mounds seem to have some connection with sun spots (solar hurricanes), but they often appear before the spots break through the sun's surface and they persist long after the spots have disappeared. Around the peaks and valleys of these gaseous mountains blow winds whose speed may be greater than 300,000 m.p.h.

Prominences. Other new instruments, which black out the sun's bright disc, leaving only the atmosphere around it, show even more startling things. The surface of the sun, even far from the "mountains," is not smooth. It is covered with tiny "spicules" that jet up suddenly. Tiny only "in the solar sense," they are several hundred miles in diameter and 5,000 to 10,000 miles high. They lick up from the surface and fade away in an average of about five minutes.

More spectacular still are the "prominences": vast, arching flames of incandescent gas ejected with enormous speed (see cut). They rise at 400,000 m.p.h. and soar to hundreds of thousands of miles above the surface. Other prominences appear out of nowhere, high above the surface, and seem to fall like water from a hose. Some of the material in prominences and other solar disturbances may be blown as far as the earth, causing the electrical storms that knock radios haywire.

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