Image source: NASA
Go outside about 9:00 p.m., weather permitting (cloudless night), early February, and look directly south. There, you will behold the most easily recognizable winter constellation, Orion, the Hunter. In Greek mythology, Orion was a gigantic hunter and is mentioned in Homer's Odyssey and Iliad and other Greek writings. He was described by several other historic world cultures, with rich mythic stories to describe his heavenly origins. He is mentioned three times in the Bible.
Orion's form is that of an hourglass asterism. An asterism is a pattern, or group of stars that may outline a constellation, such as Orion, or be part of a larger constellation. The Big Dipper is an asterism in the constellation of Ursa Major (the Great Bear), for example. Orion straddles the celestial equator, so it is visible in both the Northern and Southern Hemispheres.
Image source: Wikipedia
Four stars, Rigel (the sixth brightest star in the night sky), Betelgeuse (the ninth brightest), Bellatrix and Saiph, outline his upper and lower body. Betelgeuse is Orion's right shoulder, Bellatrix the left shoulder, Saiph the right foot, Rigel the left foot. Each of these four stars are giant, or supergiant stars. (We'll discuss star sizes and masses in a later article.) Orion's "Belt" lies in the center of the asterism and consists of threeEars: Alnitak, Alnilam and Mintaka. These are all supergiant stars.
Hanging down from his belt is Orion's Sword, a pattern of three stars. The middle "star" is not a star at all, but is the Great Orion Nebula. Here, although some gas covers the entire constellation, it is 'unmasked' in the Orion Nebula by the incredibly intense light of young, hot stars. In other words, we are looking at a stellar nursery. Some of these stars are only a half-million years old, which in astronomical terms are infant stars. With good eyesight, you can see the nebula without the aid of a telescope. In my experience, it looks like just a slightly "fuzzy" star. Obviously, a telescope brings out details, with its wispy, ghostly form taking on ever greater beauty as the telescope aperture is increased. All stars form from the effects of gravity on clumps of gas and dust between the stars (interstellar gas and dust).
Compared to the rest of the Hunter's body, the head of Orion is a tiny triangle of three stars. The topmost star of the triangle (Meissa) is also a giant star. I should- probably mention that these stars are called "giant" or "supergiant" because they are so much bigger than the Sun, our closest star. Nevertheless, they still appear as tiny points of light to our unaided vision, or even in large telescopes, because they are so far away!
Once you recognize this beautiful winter constellation, you are not likely to forget it. A planisphere can help you locate objects in the night sky, like Orion, without the need of a computerized (GoTo), or clock-driven (equatorial-mounted) telescope, and they are inexpensive.
Next time, we will talk about magnitude scales. a way to classify stars by their brightnesses.
Advanced Sky Watching Bunham, Dyer, Garfinkle, George, Kanipe and Levy. Time-Life Books 1997
Backyard Guide to the Night Sky Schneider, H. National Geographic 2009
The Night Sky (trademark) Planisphere (for 40 - 50 degrees north latitude) David Chandler Company 2014
365 Starry Nights Raymo, Chet Fireside 1982
Wikipedia (search) 01/13/2021
George Drake, M.D.
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Michiana Astronomical Society Member
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