Take some time tonight to enjoy the early evening winter sky, especially Orion the Hunter, which is the grandest constellation in the sky.

Its fame is probably only exceeded by the Big Dipper.

Orion, which actually looks like an enormous mythical hunter, will be directly south around 9 p.m. All of its main stars are bright, with its two brightest stars Rigel and Betelgeuse being the seventh- and 11th-brightest stars in the sky, respectively. Betelgeuse in Orion's right shoulder is a red star, while Rigel in Orion's left foot is a blue star.

The stars in Orion's "belt" - Alnitak, Alnilam and Mintaka - are supergiant blue stars. In fact, Orion's brightest stars represent enormous supergiant stars far larger and brighter than the sun.

Large stars are like mythical heroes who die young. Their furious lives last only a few million years. The sun is nearly 5 billion years old and will live billions of years more.

Hanging from Orion's belt is his sword, which is somewhat fainter than the belt. The Orion Nebula lies in the sword and is visible to the naked eye as a diffuse nonstar-like object. It is also called M42, because it is the 42nd entry in a famous catalog of astronomical objects compiled by Charles Messier (1730-1817) in the 18th century.

The Orion Nebula is a fabulous object in telescopes of all sizes, and spectacular images of it have been taken for more than 100 years. It is an enormous collection of dust and gas in which young stars are forming, a wonderful stellar laboratory much studied by amateur and professional astronomers.

Moon Watch

Today there is a waning (growing smaller) gibbous (more than half lit) moon. It will be at last quarter on Saturday.

Astronomical twilight ends at 7:21 p.m. tonight, leaving the sky dark until the moon rises at 10:40 p.m.

Learn more about the Proper Size of the Visible Universe

Learn more about the role black holes have in helping determine the size of the universe at Friday's meeting of the Tucson Amateur Astronomy Association.

Fulvio Melia, a University of Arizona physics professor and astrophysicist, is also an author of several books, including the "The Black Hole at the Center of Our Galaxy."

Black holes were closely studied during the "Golden Age" of relativity, from 1960 to 1974, and cosmology today finds itself at a similar stage of development. Breathtaking observations are making it possible to more fully grasp the role played by general relativity in shaping our view of the origin and evolution of the cosmos as a whole.

Also Friday, Jim O'Connor, an astronomy association member, will give an introductory talk about clusters, nebulas and more that the sky offers.

The free event starts at 6:30 p.m. at the Steward Observatory lecture hall, 933 N. Cherry Ave.

Contact Tim Hunter at skyspy@azstarnet.com