Go out on any clear night this week and look south ?and, assuming you live in the Northern Hemisphere, you will see one of the best known star groupings in the sky, the constellation Orion.
Orion is a hunter in the mythologies of many peoples around the world. His body is marked by a rough rectangle of four bright stars.
Betelgeuse and Bellatrix mark his shoulders, and Saiph and Rigel mark his knees. In between is a perfect line of three equally bright stars canted at an angle: Alnitak,? Alnilam, and Mintaka comprise the Belt of Orion. From his Belt hangs his Sword: three more stars in a vertical line, more closely spaced.
All of this can be readily seen without a telescope in all but the most severely light polluted skies. Look carefully at the two brightest stars in Orion: Betelgeuse in the upper left and Rigel in the lower right. Do they look the same color to you? Betelgeuse is a red giant: a huge ancient star glowing red and varying in brightness over time. In contrast, Rigel is a young blue giant, living life in the stellar "fast lane."
With binoculars or a small telescope, Orion is an incredibly rich area of the sky to explore. It includes a variety of double and multiple stars, and the finest nebula in the entire sky.
Rigel is a beautiful example of an unequal double star. In a small telescope, its bright primary star is accompanied by a tiny speck of a secondary star, looking much like a star with a planet.
Two of the three Belt stars are multiples. Mintaka at the right end of the belt is a wide double, and Alnitak at the left end is a triple star: a close bright pair accompanied by a distant third star.
The greatest treats, however, reside in the Sword of Orion. All three of the "stars" which make up the Sword are in fact multiple stars or star clusters ? the distinction is a hard one to make in areas as rich in stars as this. All are involved in complex nebulosity.
But it is the middle "star," Theta, which takes the prize. First of all, it is a double star, Theta 1 and Theta 2. Theta 2 is a wide double star with 5th and 6th magnitude components. Theta 1 is a quadruple star, sometimes known as The Trapezium. Four stars ranging from 5th to 8th magnitude are easily visible in a small telescope (on this magnitude scale, larger numbers represent dimmer objects, with stars around magnitude 6 being about the dimmest most people can spot from rural locations). Two more tiny stars can also be seen with a large telescope on a steady night.
But that's not all: Theta is in the heart of the Orion Nebula, the brightest nebula in the sky.
Visible in any telescope, this nebula rewards detailed study. The bright central region is kidney shaped. Under dark skies two faint wings stretch out covering an area several times larger than the moon. A dark bay, known as the Fish Mouth, divides the main Orion Nebula, Messier 42, from its smaller companion, de Mairan's Nebula (Messier 43).
There are dozens more deep sky objects awaiting the celestial explorer in Orion, including one of the most challenging objects in the sky, the Horsehead Nebula. This famous dark nebula, just south of Alnitak, is relatively easy to photograph but frustratingly difficult to see with a telescope, requiring perfect skies, a large telescope, and a special Hydrogen Beta filter.
- How to Pick a Telescope
- More Night Sky Features from Starry Night Education
- Beginner's Guide to Astrophotography