The Orion Constellation

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The Orion Constellation is easy to spot. It is one of the few constellations that most people know, even if they know little else. What makes Orion so easy to spot is his belt. Orion’s Belt or the Belt of Orion, also known as the Three Kings or Three Sisters, is an asterism in the Orion Constellation.  Three stars of similar brightness make the belt of Orion. They are (from east to west) Alnitak, Alnilam, and Mintaka. Orion’s Belt in the night sky is the easiest way to locate Orion in the sky. So, let’s begin our journey into the Orion Constellation.

ALNITAK

Alnitak, the leftmost star in the belt when seen from the Northern Hemisphere (rightmost from the Southern Hemisphere) is magnitude 1.70.  That’s fairly bright for a star, making it one of the top 35 brightest stars.  It is spectral type 09.5 Ib, which is a very hot, very bright, Supergiant.  It shines with nearly 100,000 times the light of our own Sun.  That is only magnitude 1.7 tells you that it is far away, about 800 lightyears distant, in fact.  It is a multi-star system, with two companions, with spectral types B0 and perhaps O9.5.  The name Alnitak comes from the Arabic meaning “The Girdle”.  Alnitak has Bayer designation Zeta Orionis and a Flamsteed number (Flamsteed numbers are generally preferred to Bayer designations with Roman letters) of 50 Ori.

spectral chart-The Orion Constellation
Spectral Chart

Astronomers have devised a classification scheme which describes the absorption lines of a spectrum. Although based on the absorption lines, spectral type tells you about the surface temperature of the star. One can see that there are few spectral lines in the early spectral types O and B. The Sun is an as a G2V type star, a yellow dwarf and a main sequence star. Stars are classified by their spectra (the elements that they absorb) and their temperature. There are seven main types of stars. In order of decreasing temperature, O, B, A, F, G, K, and M.

ALNILAM

The middle star of Orion’s belt is Alnilam, and it is one of the common navigation stars.  At magnitude 1.70, it is about the same brightness as Alnitak, but being the middle star of the belt makes it hard to confuse with any other star.  It is spectral type B0 Ia, only a tiny bit cooler and somewhat more luminous than Alnitak, being perhaps almost 350,000 to 400,000 times brighter than our Sun.  But, Alnilam is farther away, at between 1000 and 1300 lightyears distant. There is a very faint reflection nebula lit by Alnilam. The star Alnilam is Epsilon Orionis in the Bayer nomenclature and has Flamsteed number 46 Ori. The name Alnilam comes Arabic meaning “The String of Pearls”. It represents ornaments on Orion’s belt.

MINTAKA

The westernmost star of the belt, the one that rises first, is Mintaka (also designated Delta Orionis).  Mintaka, too, is a multiple star system, and the closest two orbit one another in only 5.7 days. Eclipsing one another, causing the magnitude of the star to vary between 2.14 and 2.26. This makes Mintaka the dimmest of the three belt stars.  It, too, is spectral type O9.5, but it is considered a giant, not a supergiant like the others, so it is O9.5 II, shining with only 70,000 times the luminosity of the Sun. The companion is a B2 V star. Mintaka 1,200 light-years from the Sun. The name Mintaka means “The Belt”.  Mintaka has a Bayer designation of Delta Orionis and a Flamsteed number of 34 Ori (δ Orionis, abbreviated Delta Ori, δ Ori).

As I said, Mintaka means Belt, and that name has been applied to the entire set of three stars.  But, so has the name Alnilam, as if the line of stars were the string of pearls, and even the name Alnitak has occasionally been used to represent the set of three stars.  Eventually, the names came to be applied individually to the indicated stars.

Each of these stars is a very massive star, with 20 to 40 times the mass of the Sun. Such stars live very short lives and die explosively as a supernova. Each of these stars is similarly far away and have similar motions in space. Undoubtedly, these stars are fairly young (as stars go) and are part of the active star-forming activity going on in the direction of Orion.

RIGEL

oricons2-The Orion Constellation

The brightest star in Orion is Rigel, located in the lower right corner of the stick figure that we often use to portray the constellation. Rigel, also designated β Orionis, is a variable star. On average, the seventh-brightest star in the night sky and the brightest star in the constellation of Orion. It is a monster star that is very bright and one of the most distant stars that you can see in the sky, but it is still one of the dozen brightest. Rigel means “foot” and represents the foot of Orion.

However, since Rigel means foot, there are more Rigels in the sky than just this one! Most any of the constellations that have a bright star near where the foot is normally supposed to have that star named Rigel. However, only two of these stars are very bright, so it is generally assumed that you mean one of those two if you talk about the star named Rigel. The other one is in Centaurus, and we often designate it Rigel Centaurus (Third brightest star), or just Rigel Kent, to differentiate it from the Rigel of Orion. To further remove confusion, Rigel Centaurus is normally referred to by its Bayer designation of Alpha Centauri.

BETELGEUSE

The star in Orion’s upper left quadrant is called Betelgeuse, which means “armpit.” Don’t blame me! I didn’t name these things! Betelgeuse is a red supergiant star. If you were to set it where the Sun is, the outer surface of the star would be from the center of the star nearly five times the distance between the Sun and the Earth. Everything inside the orbit of Jupiter in our solar system would be inside Betelgeuse. Despite its great size, Betelgeuse only has a mass dozens of times the mass of the Sun, so it is very thin and tenuous. It is also a variable star, and it pulsates somewhat, but in an irregular fashion.

oricons3-The Orion Constellation
Orion Constellation

Coming down from the belt is a line of dim stars that we refer to as Orion’s sword. Near the bottom of the sword, you can see (with good eyes and dark skies) a faint fuzzy patch. It is obvious in binoculars, and beautiful in a telescope. This fuzzy patch is called the Orion Nebula. There are some indications that it is currently brighter than it was a couple of hundred years ago, but not by so much. The Orion Nebula is a region of gas and dust (about 90% hydrogen by the number of atoms, and just under 10% helium, with just under 1% other stuff). This gas and dust are collapsing to form new stars.

Also Read: The Cosmic Cloud-Nebula

In fact, the Hubble Telescope has shown several solar systems in this nebula that are in the process of forming. The first stars that form out of such a nebula are the biggest, brightest, and hottest stars, which produce a huge amount of ultraviolet light. The UV light then can ionize the gas in the vicinity of these stars. As electrons recombine with the protons to form neutral hydrogen again, then the hydrogen emits light. Much of this light is reddish, so color photographs of the Orion Nebula often show pretty red and pink colors. Don’t expect to see the color in a small telescope though. However, even rather small amateur telescopes can be used with cameras taking time exposures to produce these colors. To illustrate how big and bright the nebula is, just think that you are seeing it with the naked eye (dark skies) from over 1500 lightyears away!

I hope you like the content of the above article about The Orion Constellation. All the information’s are collected from different online sources.


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