If you look up at the constellation Orion you can find some fascinating objects to observe. You can easily find Mintaka, Alnilam, and Alnitak, the three stars that make up Orion’s belt. The star that marks the shoulder of Orion the hunter, up and to the left of Orion’s belt is Betelgeuse and the star to the lower right of the belt is Rigel.
The Orion constellation is a favorite of backyard astronomers as it contains two of the ten brightest stars in the sky. Astronomers use different terms when discussing luminosity or brightness of an astronomical object. The Apparent magnitude of an object is how bright the star appears from Earth. There are two reasons why a star may appear bright to us. The first reason is that the star may be very close to us. The second reason is that the star may actually be highly luminous. Of course a star could be close to us and be intrinsically bright. Absolute magnitude is the magnitude a star would have if it was at a distance of 10 parsecs from the Earth. If all the stars were at the same distance from Earth, 10 parsecs, then it would be obvious which stars were actually brighter. Absolute magnitude is a measure of how bright the star actually is regardless of its distance from an observer. 1 order of magnitude is equal to 2.512 time brighter. Lower magnitude values translate to brighter stars. Betelgeuse is easily recognizable by it’s reddish color. It has an apparent magnitude of .45 and an absolute magnitude of -5.14. Rigel has a bluish color and has an apparent magnitude of .18 and an absolute magnitude of -6.69. The fact that Rigel has a lower magnitude indicates that it is brighter or more luminous than Betelgeuse.
So are there other interesting objects besides stars in the Orion constellation? Actually yes. The closest stellar nursery to Earth can be found in this constellation. Nebula, according to NASA “are enormous clouds of dust and gas occupying the space between the stars.” So how does a star form out of a nebula? According to Hubblesit.org. when regions of mass and dust within the nebula are sufficient enough so “that the gas and dust can begin to collapse from gravitational attraction. As it collapses, pressure from gravity causes the material at the center to heat up, creating a protostar. One day, this core becomes hot enough to ignite fusion and a star is born.”
The Orion Nebula is the closest star forming region to us at a distance of 1,350 light years away and is believed to be 2 million years old. The nebula is more than 30 light years in diameter. As a refresher a light year is a measure of distance and not time. A light year is the distance light can travel in one year which is approximately 6 trillion miles or 9.7 trillion kilometers. The Orion Nebula or Messier 42 (M42) has an apparent magnitude of 4.
It’s easy to locate the Nebula according to Science Focus “…look below the three stars of Orion’s Belt (or above, if viewing from the southern hemisphere). You will see a faint line of stars, which make up Orion’s sword. The nebula is halfway down the sword and will appear as a fuzzy-looking star”
Four stars are visible from an open cluster in the central region of the nebula. An open cluster is a loosely bound collection of several thousand stars which are relatively young. This cluster is known as the Trapezium based on their trapezoidal configuration. The Orion Nebula is part of a larger stellar network called the Orion complex. According to Astronomy.com the complex contains “. ..a mixture of cold hydrogen and dust grains. M42 is known as an emission nebula. The hydrogen is excited by the hot stars buried within. Excitation is a process by which hydrogen atoms absorb energy (from nearby stars). The atoms can’t hold the energy for long, however, and quickly release it as light.”
M42 contains “… contains hundreds of very young stars, less than a million years old, and also protostars still embedded in dense gas cocoons. The nebula is home to about 700 stars in different stages of formation. The youngest and brightest members are believed to be less than 300,000 years old, and the brightest of these may be as young as 10,000 years old.” (messier-objects.com) Feel free to take a tour through the Orion Nebula in infrared and visible light: https://youtu.be/fkWrjrdT3Zg
The best time of year to view the Orion constellation including the Orion Nebula is in December and January when the constellation is at its highest point in the sky for the Northern Hemisphere. The Orion Nebula is a bit unusual in that it can be observed with the naked eye in areas with very dark skies. Most nebula are not visible without the aid of a binoculars or a telescope. Now that you know a little about Orion go find a dark sky location and have a look for yourself I promise you won’t be disappointed.
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