Deep Space objects in Orion
 The Great Nebula of Orion (M42) is one of the most photographed objects in the sky. It is visible to the unaided eye as a fuzzy spot about halfway down the sword of Orion. This area is a collection of gas and dust where stars are being born. The central bright star that is illuminating the gaseous cloud is actually four stars known as the Trapezium. The nebula itself is one of the nearest regions of star formation at only about 1,500 light years away. It has formed stars recently, only 300,000 years ago. The nebula is populated with many newly created stars and protostars.
The Orion Nebula is an emission nebula, giving off light from its own glowing gases, as well as being illuminated by the Trapezium. This was the first nebula to be successfully photographed, in 1880 by Henry Draper. The Orion nebula is Messier Object number 42 (M42), the 42nd object that Charles Messier added to his famous catalogue of objects. M43 can be seen in this photograph directly above M42. Both objects are part of a larger group that includes the Horsehead Nebula as well.
Photograph of the Orion Nebula by David Malin. Copyright © ROE/Anglo-Australian Observatory. Photograph produced from UK Schmidt Plates. Used by permission.
|
Star Colors in Orion
 You can probably recognize Orion in this photograph by the three stars in the belt. The photograph was exposed for about a half an hour. The stars were in focus to start, but every few minutes, the focus was adjusted to make the stars more and more out of focus. The gradual loss of focus combines with the natural movement of the stars across the sky to produce an image where star color is made more obvious. This technique, called a step focus, was discovered by accident by the well known photographer David Malin, who took this picture.
The photograph illustrates that stars have very different colors from one another. Color tells us about a star's temperature, composition, age, size and even its distance from us. Red stars are generally older, cooler stars that have used up much of their hydrogen fuel. Blue stars are generally younger and hotter. (In astronomy, the phrase "red-hot" doesn't work.)
Most of these stars are blue, with the obvious exception of the very red star Betelguese (located at Orion's right shoulder). Betelgeuse is a red supergiant. Rigel, the blue star at the lower left is a blue supergiant. The red streak in the sword area is the Orion Nebula.
Betelgeuse is diferent from the other stars here in that it is at the end of its life; it has burned up much of its hydrogen fuel and is much cooler than the blue stars. Small stars like the Sun conserve their energy and last for billions of years. Large, hot stars like Rigel burn up fast and may last only a few million years. The Sun is the kind of star where life and intelligence can have the time they need to evolve. Our Solar system is 4.6 billion years old and will probably last another 4 or 5 billion years.
Photograph of Stars in Orion, Step Focus by David Malin. Copyright ©Anglo-Australian Observatory. Push Processing, Hasselblad. Used by Permission.
|
The Individual Stars of Orion
 These are the "common names" for Orion's individual stars, but astronomers often refer to stars by their Greek letters, also shown here. An astronomer named Johann Bayer assigned lower case Greek letters to the stars in each constellation, often in order of brightness. Thus, Betelgeuse is alpha Orionis, Rigel is beta Orionis, etc. (The form Orionis is the Latin genitive case; it is the possessive, and means "of Orion.") Astronomers use these Greek letters and the genitive case to identify stars.
Common names for stars are often Arabic. During the middle ages, the Arab world kept the ancient Greek knowledge of astronomy alive. They were interested in the individual stars and named many of them. These names are often descriptive and colorful. For example, Betelgeuse means "armpit of the central one." Orion may have been called the Central One (Al Jauzah) because it is directly over the Earth's equator. Betelgeuse was discovered to be a variable star by Sir John Herschel in 1836. Betelgeuse has a companion star with a five year orbit; we know that from examining the spectrum of the star, so Betelgeuse is called a "spectroscopic binary."
Rigel means "left leg of the Jauzah." It is a blue super giant and also a double star. It is the seventh brightest star in sky. Some stars are bright because they are nearby and others are bright because their absolute magnitude (true brightness) is very great. Rigel is both: it is only about 910 light years away and it is about 150,000 times as bright as the Sun.
Bellatrix is known as the Amaxon Star. "Women born under this star shall have mighty tongues," (T. Hood). Mintaka means "the belt," in arabic. It is the northernmost star in the belt and is very the near celestial equator. Alnilam means "the string of pearls." It is the central star of the belt. Saiph means "sword."
|
The Mythology of Orion
 Orion, from the Greek word for "warrior," was the mighty hunter. The Syrians called him Al Jabbar, the giant. He was so tall he could wade through any ocean on Earth. He was also the most beautiful man in the world, and his story is filled with exploits. He was blinded by one lover, only to have his sight restored by another. Orion fell in love with all seven of the Pleiades, the seven sisters, and he pursued them all. Zeus placed the sisters in the sky to spare them heartache, but Orion still pursues them across the sky.
Orion was a bad omen for sailors, signifying the beginning of the winter and of winter storms. The Chinese called Orions belt "Tsan," meaning "Three side by side.
Orion and Scorpius are never seen in the sky together, because they are located in opposite directions from one another. The story arose that the sky was not big enough for both of them. Scorpius the scorpion stung Orion to death. Orion is said to fear the poisonous sting and to flee the scorpion's arising each night.
Urania's Mirror, by "A Lady." Published by Samuel Leigh, London, c.1825.
|
| Location of Orion
|
This is Orion, the brightest constellation in the sky. It is easy to find if you look for the three bright stars that make up Orion's belt. Once you have found this distinctive pattern, two other very bright stars will help you define the rest of the constellation. The first star, Betelgeuse, is located at Orion's right shoulder. The second, Rigel, is at his lower left.
Orion is visible from every part of the Earth. It is located on the celestial equator. This line is a projection into space of the Earth's equator and is shown here as a green line. Early navigators relied on the constellations as they travelled, and distinctive stars like the three in Orion's belt were important to them.