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Using Orion to find Stars and Constellations

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Raul finished his education with a B.S degree in Mathematics and a Minor in Physics. Recently, he became an amateur stargazer.

In this article I want to show a few tricks that can be used to locate various stars or constellations using the stars from the constellation Orion. Orion is useful as a reference constellation because it has many stars with an apparent magnitude under 3 ( which means they are very bright), it is fully visible at latitudes between 79º N and 67º S (pretty much the inhabitable range), it is a big constellation and it is easy to identify it in the sky. We will also see that Orion is in the neighborhood of very important stars or constellations.

When you look in the astronomy books, the constellations are usually shown as asterisms or patterns where various stars are connected by lines. These asterism patterns look like stick figures. Unfortunately, you will see that sometimes the astronomy books show a slightly different pattern or stick figure for the same constellation. Another problem is that some stars from a constellation are too dim to be seen with the naked eye (especially if you live in a city). In this guide I will focus on how to find the brightest stars from various constellations. After you find the brightest star or stars from the constellation, you can use these stars as reference and then use your imagination to create the constellation patterns.

Orion

Before we find stars from other constellations using Orion, we must know how to identify Orion. In Figure 1, we can see the general neighborhood of Orion as seen from my location in the Northern hemisphere. We can see that Orion is under the ecliptic line (path of the Sun), and like the Sun it will usually have a Southern direction. If you are in the Southern hemisphere, Orion will be upside down, above the ecliptic and it will usually have a Northern direction.

Sky around Orion

Figure 1: The area around Orion and the ecliptic

Figure 1: The area around Orion and the ecliptic

The constellation Orion has about 8 stars that are very bright. Betelgeuse and Bellatrix seem to be the 2 armpits of Orion (Figure 2). Alnitak, Alnilam and Mintaka form Orion’s Belt. Under Orion’s Belt you can see the star Hatysa. Near Hatysa, there is the Trapezium Cluster and the Great Orion Nebula. Hatysa, the Trapezium Cluster and the Great Orion Nebula form Orion’s Sword or Orion’s Dagger. Finally, the stars Saiph and Rigel are the 2 legs of the constellation. The pattern made by Betelgeuse, Bellatrix, Orion’s Belt, Saiph and Rigel looks like a butterfly.

Orion

Figure 2: the stars of Orion

Figure 2: the stars of Orion

Beginners should know that the astronomical reference materials sometimes use the Arabic or Greek names for the stars and sometimes they use the Bayer designation. The Bayer designation names a star using a Greek letter and the genitive form of the constellation it belongs (the names of the constellations are in Latin). For example, Betelgeuse is also known as Alpha Orionis (alpha of Orion). Usually the stars are named according to their brightness, using the standard Greek alphabet. Thus, alpha should be the brightest star, beta the second brightest star and so on. Unfortunately, you will find out that sometimes the beta star or even the gamma star is actually the brightest star in the constellation. Rigel is also called Beta Orionis, but it is usually the brightest star in Orion. Betelgeuse is a variable star, and sometimes it will be brighter than Rigel. More confusion is added by the fact that sometimes the same star has more than one Arabic name and sometimes one of its names is shared by another star.

Orion’s Belt, Sirius, and Taurus

One of the most well know tricks is to use Orion’s Belt in order to find the star Sirius from the constellation Canis Major. In Figure 3 you can see that if you draw a line through Orion’s Belt and extend it beyond Alnitak, the line will pass very close to Sirius. Sirius is a very important star since it is the brightest star seen from Earth (besides the Sun).

If we look in the opposite direction, beyond Mintaka, the line will through the Taurus constellation. When you are in the field and follow the line in this direction, you will immediately know which star is Aldebaran, since it is by far the brightest star in Taurus. Closer to the line and just below Aldebaran, is the Hyades Cluster, which is not labeled in Figure 3. In Figure 3 you can also see that the line passes very close to the Pleiades Cluster, with Alcyone being the brightest star from the cluster.

Orion's Belt, Sirius and Taurus

Figure 3: Orion's Belt points towards Sirius, Aldebaran and Pleiades

Figure 3: Orion's Belt points towards Sirius, Aldebaran and Pleiades

Gemini and the Rigel-Betelgeuse axis

The brightest stars from the constellation Gemini are Castor and Pollux. The stars are close to each other and they represent the heads of the 2 mythological brothers. The easiest way to find the pair is to draw an imaginary line that goes from Rigel and extends beyond Betelgeuse. In Figure 4, you can see that the line passes very close to Castor. You can also see that the line passes very close to Alhena, which is the 3rd brightest star in Gemini

Gemini and the Rigel-Betelgeuse axis

Figure 4: the Rigel-Betelgeuse axis points towards Castor

Figure 4: the Rigel-Betelgeuse axis points towards Castor

Leo, Canis Minor, Cancer and the Bellatrix-Betelgeuse Axis

The brightest star from the constellation Leo is Regulus. The easiest way to find Regulus is to draw an imaginary line that goes from Bellatrix and extends beyond Betelgeuse. In Figure 5, you can see that this extended line passes very close to Regulus. Once you know where Regulus is, you can use it as a reference to find other important stars from Leo.

You can see that the same line also passes very close to the constellation Canis Minor, which has only 2 stars. The star Procyon is easy to spot since it is brighter than Betelgeuse. The star closer to the line but not labeled in the image is Gomeisa, which has an apparent magnitude under 3. Thus, both stars should be visible.

The line also passes near the brightest stars from the constellation Cancer. All the stars that belong to Cancer have an apparent magnitude well above 3, so they are dim especially if you are in an urban area.

Leo, Canis Minor, Cancer and the Bellatrix-Betelgeuse Axis

Figure 5: the Bellatrix-Betelgeuse Axis points towards Regulus, Procyon and a few Cancer stars

Figure 5: the Bellatrix-Betelgeuse Axis points towards Regulus, Procyon and a few Cancer stars

Some Recommendations

Before I finish this article, I want to make a few useful recommendations. There are a few useful free tools that can help beginners learn about the sky. The first tool is the Stellarium free-software planetarium. You can use Stellarium to simulate the movement of the sky for your location in real time. Stellarium allows you to click on stars and other sky objects in order to get real time data on their apparent magnitude, position, color index etc. The second free tool is a phone app like Sky Map. With Sky Map you can point your phone in any direction to see what constellation you can find in that direction. This app can be very useful when you are in the field.

If you want to buy a book you can buy “Atlas of the Constellations” by Giles Sparrow. The book has useful information about all the 88 constellations, including the time of the year when a constellation is most visible or the range of latitudes where the constellation is fully visible. The book can be useful when you are in the field stargazing.

Finally, you can check my second article about the constellation Orion. In the second article, I use the same method to find additional stars and constellations using the stars of Orion.

Comments

Doris James MizBejabbers from Beautiful South on March 11, 2019:

Astronomy has always been confusing to me. Even reading your descriptions doesn't really clarify where each one is in my mind. I guess I'm just not meant to understand it. However, it is interesting, and I thank you for a fine article.

threekeys on February 18, 2018:

Thank you Raul for pointing me in the right direction. Peace to You

RaulP (author) on February 18, 2018:

Hi Threekeys,

If you are interested in esoteric mathematics maybe you can read this translation of Iamblichus https://archive.org/details/iamblichus-theologyari... . Mythology is connected to astronomy. Actually, there is a strong case to be made that mythological stories are mnemonic devices for the movement of the sky. See "mathisen corollary" channel on Youtube.

If you are interested in renaissance architecture maybe you can find a translation of "De re aedificatoria" by Alberti

threekeys on February 18, 2018:

Enjoyed your article and the offerings in how you can start looking at the night sky.

I used to be into mythology; and if I had the mathematical ability I would have liked to have explored eosteric mathematics.

Numbers music and Renaissance architecture....

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