Some tips on sky-watching

Some tips on sky-watching

Jim Kaler, a longtime UI professor, offers these tips for star-gazing in his lectures for Osher Lifelong Learning Institute at the Urbana campus.

As the Dipper is to northern hemisphere spring and summer, Orion — the hunter — is to winter, his three-star belt prominently crossing the sky close to the celestial equator. He's most famously depicted as raising his club against charging Taurus, the bull, which lies to the northwest.

Look down from the belt to the sword he carries below. Even binoculars will reveal the center of the sword to be surrounded by the Orion Nebula, a huge cloud of glowing interstellar gas lit by hot stars that is the marker of a great star-forming engine some 1,500 light years away.

At his right shoulder — he is facing you — is the first magnitude star Betelgeuse. One of the larger stars in the galaxy, this cool "red supergiant" would nearly fill the orbit of Jupiter. At a distance of nearly 600 light years, the great star shines with the light of 85,000 suns, implying a mass nearly 20 times that of the sun.

Down and to the left of Orion, we find the opposite extreme. Here, in Canis Major — Orion's larger hunting dog — shines Sirius, the brightest star in the sky. It's not only intrinsically bright, but it's close too — only nine light years away. Betelgeuse, a fine example of a dying massive star that is destined to explode, will produce a remnant far smaller, a 30-kilometer "neutron star."

Betelgeuse and Sirius are the northwestern and southern apices of the Winter Triangle, which also includes Procyon in Canis Minor — the smaller dog — at the northeastern corner.

The Winter Triangle's clone is the Summer Triangle. It is made of Vega — in Lyra, the lyre — at the northwestern apex, Deneb — the tail of Cygnus, the swan — at the northeastern point, and Altair — in Aquila, the eagle — at the southern. The triangle frames the Milky Way.

Vega, the third brightest star in the northern hemisphere, is surrounded by an infrared-radiating disk that implies a circulating planetary system, though no planet has ever been seen.

First magnitude Deneb is fainter than Vega — 25 light years away — only because of its great distance of 1,400 light years. If this white supergiant were placed at Vega's distance, it would shine 15 times more brightly than Venus, cast modest shadows and be easily visible in daytime.

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