Gazing Toward Orion
we are looking edgewise into the disk of the Milky Way galaxy. The center of the galaxy is in just the opposite direction. So we are looking outward along one of the spiral arms of the galaxy. There are fewer stars in this direction, but those that are there are generally closer, and many are brighter. Certainly there are a good number of interesting stars and other deep-sky objects to consider.
Rigel and Betelgeuse are the two brightest stars in Orion, which is the only constellation within our vision to boast of two first-magnitude stars. The only other such constellation is Centaurus, which can be seen only from southern skies. In addition, Bellatrix, Alnilam, and Alnitak (Gamma, Epsilon, and Zeta Orionis) shine at magnitudes between 1 and 2, with Saiph (Kappa Orionis) at magnitude 2.05 close behind in the list of 51 brightest stars. Together, these stars form one of the most distinctive of all constellations.
Betelgeuse is Alpha Orionis, although Rigel (Beta) is a little brighter, on average. Betelgeuse pulsates irregularly, varying from a brightest 0.4 to about 1.2. The two stars are at about the same distance from us, about 1400 light years. The two are quite different, however. Rigel is a hot blue supergiant star, burning its hydrogen fuel at a prodigious rate. About 50 times the mass of the Sun, it is 57,000 times as luminous. Betelgeuse is a red giant, so huge that its diameter has been measured by direct interferometer means. It would encompass the orbit of Mars if it were placed at our Sun's position.
The three stars that form Orion's belt, prominent in the sky mythology of a number of cultures, are Delta, Epsilon, and Zeta Orionis, from northwest to southeast. Their respective names are Mintaka, Alnilam, and Alnitak. For the Chumash Indians of California these stars were simply called Three In a Row, and their location in the sky served as a calendar to mark ritual events.
Of these three stars of Orion's belt, Mintaka has the distinction of having a declination of almost exactly zero; its rising marks the east on the horizon, its setting the west. So it is not surprising that this star was of special consideration to astrologers, who avowed that it meant good fortune.
The Great Orion Nebula, M42, is a huge interstellar gas cloud 20,000 times the diameter of our solar system. Here stars like our Sun are being born; as they ignite, their radiation causes the gas cloud to glow with different colors. Photograph by R. S. Hoyle; 40-minute exposure on gas-hypered Ektachrome P1600 film, using an 8-inch SCT; f/10.
 
 
 

 
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