Today’s release of NASA’s Astronomy Picture of the Day features the Orion Nebula. Although this photo was made with a large telescope, many of its features can be seen with binoculars or a small telescope.
In publications, discussions of the features of a constellation usually include a diagram. For Orion, let’s make an exception and try to find a few things using words only!
Betelgeuse
Of Orion’s two brightest stars, Betelgeuse (pronounced “Beetle juice”) is the distinctly orange one. It is at the “shoulder” of the hunter. Betelgeuse is classified as a “Red Supergiant” star. Its diameter is about 650 times that of our Sun. If it was at the center of our solar system, it would engulf Mercury, Venus, Earth, and Mars.
“Red supergiant” refers to a phase late in the life of many stars. Early in life, Betelgeuse was much smaller. When its supply of hydrogen fuel was used up, the star swelled to its current size. The next major event would be a supernova explosion. This is expected “soon” in astronomical terms, meaning in a thousand years, or so. This event would be quite spectacular, but may also be dangerous because of the gamma rays which would be released.
The Orion Nebula
So much for the end of a star’s life cycle. Moving to the other side of the Hunter’s belt, we find the Orion Nebula, which is full of stars at their beginning stages. The Orion Nebula is very close to the Hunter’s belt of three stars. In Northern latitudes, look below the star at the left of the belt. In Southern latitudes, look above the star the right. The Orion nebula appears as a fuzzy mass. In the city, it may not be visible to the naked eye.
The term nebula means “a cloud of gas or dust in interstellar space”. Virtually all of the gas in a nebula is hydrogen. The hydrogen in a nebula pulls together into a compact mass, through gravity. This process takes millions of years. If enough hydrogen is available, the molecules will be forced together tightly enough to start a nuclear fusion reaction. This is the birth of a star.
With a telescope, many more of Orion’s features come into view. Orion is a favorite of amateur astronomers, and an important study area for researchers. It is a constellation which “has something for everyone”.
Keep looking up!
John
Real Simple Astronomy 