Orion Constellation – The Hunter in the Night Sky

In this article, we’ll be sharing with you everything you need to know about the constellation of Orion, including how to find it, deep space objects contained within it, and how to use it to find other night sky objects more easily.

The Constellation of Orion

Orion is one of the oldest constellations and was known to many ancient cultures including the Hittites, Babylonians, ancient Egyptians, and ancient Greeks. The Greek astronomer Ptolemy cataloged this constellation more than 2000 years ago.

In Greek mythology, Orion was a handsome hunter. Most of the Greek myths about Orion end with him either battling a scorpion or being killed by it. In one myth, Orion boasted that he would kill every animal on Earth, angering the goddess Gaia who sent the scorpion. In another, he attempted to force himself on Artemis and she sent the scorpion, and in a third, he tried to save Leto from a scorpion and was stung.

These myths share the common outcome that Orion and the scorpion were placed on opposite sides of the sky, giving us the constellations of Orion and Scorpius.

One myth that doesn’t feature a scorpion has Orion falling in love with the seven daughters of Atlas and Pleione (the Pleiades). In a second, Artemis falls in love with Orion and her brother Apollo tricks her into fatally shooting Orion as a means of preventing Artemis from breaking her vow of chastity.

To help you spot Orion, here’s what SkySafari shows.

Showing an image of Orion the Hunter superimposed on the constellation of Orion
Orion, the Hunter

Orion has an area of 594 square degrees making it the 26th largest of the 88 recognized constellations. Its asterism, ‘Orion’s Belt’, is one of the most prominent asterisms in the sky.

If you’ve observed the annual Orionid meteor shower (peaks ~Oct 21) you may recognize this constellation as the location of its radiant. Additionally, this constellation contains two of the ten brightest stars in the night sky, Rigel and Betelgeuse.

Unlike most other constellations, the area of the sky designated part of Orion pretty much matches the shape of the constellation we’re familiar with, as shown in the image below.

Area of Orion, IAU boundaries shown as blue lines
Area of Orion, IAU boundaries are shown as blue lines (click for full-screen)

In the next section discover how to find Orion.

How To Find Orion In The Night Sky

Orion is part of the Orion family of constellations and is visible to observers at latitudes between +85° and -75°.

Northern Hemisphere observers can see Orion in the evening from late autumn to early spring, while Southern Hemisphere observers can see it during their summer months. The constellation of Orion is bordered by the constellations Eridanus, Gemini, Lepus, Monoceros, and Taurus, as shown in the image above.

Orion is known as a ‘trivial’ find because it is so recognizable, i.e. we don’t need to begin our hunt somewhere more obvious and move towards it.

Instead, face generally south on a fall/winter evening, and carry out a naked-eye search for the four bright ‘corner’ stars, Betelgeuse, Bellatrix, Rigel, and Saiph, and the three bright stars of Orion’s Belt, Mintaka, Alnilam, and Alnitak.

These are all shown clearly in the image below, which you can click on to get a full-screen version.

Showing the brightest stars of Orion to make it easy to find
The bright stars of Orion make it a trivial find (click for full-screen)

To find Orion’s exact position for your location on any night, use software such as Stellarium (free) or SkySafari 6, which is paid software used to generate the images on this page.

Orion’s Brightest Stars

Orion has a large number of bright stars, which is part of the reason it is so easily recognized. Below, we look at all the stars brighter than magnitude five, which are shown with their formal names on the image below.

The image, from SkySafari 6, is quite crowded, so click on it to open up a full-screen version.

The bright stars of Orion
The bright stars of Orion, click for full-screen

Alpha Orionis (Betelgeuse) – This variable, double star has a combined magnitude of 0.45, making it the second brightest star in Orion and the ninth brightest star in the night sky. This star marks Orion’s right shoulder.

The 0.56 magnitude orange-red supergiant primary and 14.50 magnitude secondary components are 38.0 arcseconds apart. The primary is a semi-regular, pulsating variable whose magnitude varies from 0.4 to 1.3 over a period of ~5.7 years and has a shorter period of 150-300 days.

Hipparcos satellite measurements suggest Betelgeuse is 425 light-years away but more recent measurements suggest 500-840 light-years.

Betelgeuse, Sirius (in Canis Major), and Procyon (in Canis Minor) form an asterism known as the Winter Triangle. Along with Rigel, Aldebaran (in Taurus), Capella (in Auriga), and Castor and Pollux (both in Gemini), Betelgeuse forms another asterism known as the Winter Hexagon.

Beta Orionis (Rigel) – This is the brightest star in Orion and the seventh brightest star in the night sky. The 0.28 magnitude blue-white supergiant primary and 6.80 secondary components are 9.4 arcseconds apart.

While Hipparcos satellite measurements suggest Rigel is 775 light-years away, spectroscopic estimates suggest 700-900 light-years. Rigel is a binary star, the B component is a spectroscopic binary in its own right, meaning it has a companion star but not one we can see in a telescope.

‘Rigel’ is derived from the Arabic for ‘foot’ and this star is located near Orion’s left foot.

Gamma Orionis (Bellatrix) – Is the third brightest star in Orion. It is also a double, but the B star is too faint for most backyard telescopes at magnitude 13.13. The primary shines at magnitude 1.65 and is a blue-white color giant star.

Bellatrix is 240 light-years away and marks Orion’s left shoulder. Its name is Latin for ‘the female warrior’.

Delta Orionis (Mintaka) – This double star is the seventh brightest star in Orion and the westernmost star in Orion’s belt. The 2.23 magnitude blue-white giant primary and 14.20 magnitude pale blue secondary components are 33.4 arcseconds apart.

Mintaka is 900 light-years away. It’s the closest bright star to the celestial equator and rises and sets almost exactly east and west.  ‘Mintaka’ is derived from the Arabic for ‘belt’.

Epsilon Orionis (Alnilam) – This is another double star and the fourth brightest in the constellation of Orion; it is the middle star in Orion’s belt. The 1.75 magnitude blue-white supergiant primary and 11.34 magnitude secondary components are 179.3 arcseconds apart.

Alnilam is 1,340 light-years away and its name is derived from the Arabic phrase meaning ‘string of pearls’.

Zeta Orionis (Alnitak) – This is a multiple star system and the fifth brightest in Orion. It is also the easternmost star in Orion’s belt.

The 1.74 magnitude blue supergiant primary and 3.70 magnitude blue-white giant secondary components are 2.2 arcseconds apart. There is a 5.21 magnitude tertiary component and a 9.55 magnitude quaternary component, which is probably an optical companion (i.e. not gravitationally associated with the other stars).

Alnitak is 820 light-years away from Earth and its name derives from the Arabic word for ‘girdle’.

Eta Orionis (Saipha al Jabbar) – This variable double star is 900 light-years away. The magnitude 3.39 blue-white main sequence primary, and its magnitude 4.87 secondary component are 1.8 arcseconds apart.

While its traditional name is derived from the Arabic phrase for ‘sword of the giant’, it is the stars Kappa Orionis and Iota Orionis that more commonly represent the sword of Orion.

Iota Orionis (Nair al Saif) – Is yet another bright double star, this one is 1,300 light-years away from us. The magnitude 2.77 blue giant primary and its magnitude 7.73 secondary component are 11.6 arcseconds apart.

This star is also famed for being the location of the Orion Nebula (M42), one of the brightest and most spectacular nebulae in the night sky.

Its traditional name means ‘bright one of the sword’ in Arabic.

The Orion Nebula
The Orion Nebula (source)

Kappa Orionis (Saiph) – This 2.05 magnitude blue-giant star is the sixth brightest in Orion and marks the lower-left corner of Orion’s main quadrangle.

Saiph is 720 light-years away. Its traditional name comes from the Arabic phrase meaning ‘sword of the giant’.

Lambda Orionis (Meissa) – This double star is 1,100 light-years away and marks Orion’s head.

The 3.39 magnitude blue-white giant and its 5.45 magnitude blue-white dwarf secondary component are 3.4 arcseconds apart.

‘Meissa’ comes from the Arabic phrase for ‘the shining one’.

Mu Orionis – This double star is 155 light-years away. The white main sequence primary shines at magnitude 4.13, while its secondary is magnitude 6.27. They are too close together to be separated in a regular telescope.

Nu Orionis – This 4.42 magnitude blue-white main-sequence star is 516 light-years away. Its mass is seven times that of our Sun, it is 4.4 solar diameters in size, and 3.3 times hotter than the Sun.

Xi Orionis – This double star is 607 light-years away. The 4.46 magnitude blue-white subgiant primary and magnitude 13.00 secondary components are 37.8 arcseconds apart.

Omicron1 Orionis – Sitting in the northwest corner of Orion, close to the boundary with Taurus, this is a magnitude 4.73 orange-red star. It is a pulsating semi-regular variable with a magnitude variation from 4.7 to 4.9 over 30 days. Omicron1 Orionis is 651 light-years away.

Omicron2 Orionis – This double star is 186 light-years away. The 4.07 magnitude orange giant primary and its 11.30 magnitude secondary component are 39.5 arcseconds apart.

Pi1 Orionis – Is 116 light-years away and is another double star. The primary shines at magnitude 4.65 and is a white, main-sequence star. The secondary component shines at magnitude 8.95 magnitude and is 172 arcseconds from the primary.

Pi2 Orionis – This 4.36 magnitude white main sequence star is 224 light-years away. It is 1.6 times hotter than the Sun, 3.5 times the Sun’s diameter, and 2.7 times the Sun’s mass.

Pi3 Orionis (Tabit) – Is a double star located just 26 light-years from Earth. The primary is a magnitude 3.19 magnitude yellow-white main-sequence star (like the Sun), its secondary shines at magnitude 11.31 and is 73 arcseconds away.

Pi4 Orionis – This 3.68 magnitude blue-white giant is 1,052 light-years away. It is an eruptive variable whose magnitude varies from 3.6 to 3.7 with an unknown period.

Pi5 Orionis – This 3.71 magnitude blue-white giant is 1,342 light-years away. It’s a rotating variable whose magnitude varies from 3.66 to 3.73 with a period of 3.7 days.

Pi6 Orionis – This 4.46 magnitude orange giant is 945 light-years away. It’s an eruptive variable whose magnitude varies from 4.4 to 4.5 with an unknown period.

Rho Orionis – This double star is 350 light-years away. The 4.48 magnitude orange giant primary and 8.50 magnitude secondary components are 6.4 arcseconds apart.

Sigma Orionis – This quintuple star system is 1,150 light-years away. The 3.79 magnitude blue main-sequence primary and 8.43 magnitude secondary component are 0.3 arcseconds apart. The tertiary and quaternary components are dwarf stars with magnitudes of 6.52 and 6.66.

Tau Orionis – This double star is 494 light-years away. The 3.59 magnitude blue-white giant primary and 11.00 magnitude secondary component are 33 arcseconds apart.

Upsilon Orionis – Is a magnitude 4.61 blue main-sequence star 2,861 light-years away.

Phi1 Orionis – This unsplittable double star is 1,087 light-years away. The primary shines at magnitude 4.40 magnitude and is a blue-white giant star. The secondary component is 0.1 arcseconds away and its orbit is unknown.

Phi2 Orionis – This 4.09 magnitude yellow-orange giant is 117 light-years away. It is fractionally more massive than our Sun (1.1 solar masses) but 9.4 solar diameters in size and 19% cooler than the Sun.

Chi1 Orionis – This double star is only 28 light-years away from Earth. Its magnitude 4.40 primary is a yellow main-sequence star. The magnitude 7.5 secondary is 0.1 arcseconds away and so too close to be resolved in a backyard telescope.

Chi2 Orionis – This double star is 1,802 light-years away. Again, the two component stars are too close to be split in a telescope. The primary is a magnitude 4.63 magnitude yellow-white supergiant, while the B component shines at magnitude 6.30.

Psi Orionis – This double star is 1,136 light-years away from Earth. The 4.61 magnitude yellow-blue subgiant primary and its 8.62 magnitude secondary are 3.0 arcseconds apart.

Omega Orionis – This 4.53 magnitude blue-white giant is 1,382 light-years away. It is nine times larger than the Sun, 12.2 times the Sun’s mass, and 3.6 times hotter than the Sun.

Star Hopping From Orion

Orion is the starting point for several star hops.

Sirius – Draw an imaginary line from Mintaka to Alnitak (~3°) in Orion’s Belt. Extend this line ~20° to Sirius, the brightest star in the constellation Canis Major.

Aldebaran – Draw an imaginary line from Alnitak to Mintaka (~3°) in Orion’s Belt. Extend this line ~20° to Aldebaran, the brightest star in the constellation Taurus.

Follow Orion's Belt to find Aldebaran and Sirius
Follow Orion’s Belt to find Aldebaran and Sirius (click for full-screen)

Pollux – Draw an imaginary line from Mintaka to Betelgeuse (~10°). Extend this line ~30° to Pollux, the brightest star in the constellation Gemini.

Capella – Draw an imaginary line from Alnilam to Meissa (~11°). Extend this line ~36° to Capella, the brightest star in the constellation Auriga.

M42 – Draw an imaginary line from Alnilam toward Orion’s feet. You should see a row of three dim stars, oriented north-south ~5° from Alnilam. The fuzzy middle star is M42, the Orion Nebula.

M78 – The bright nebula M78 is 2.5° northeast of Alnitak. Draw an imaginary line ~1° north from Alnitak to blue-white star HR 1952, extend this line another 1.5° to HR 1955, then draw an imaginary line 1.5° east to M78. See details here.

Objects To See Within Orion

Orion contains three Messier objects and some other deep sky objects for small telescopes.

M42 (NGC 1976, Orion Nebula) – This bright nebula has a magnitude of 4.00 and an apparent size of 85.0 x 60.0 arcminutes. It is 1,350 light-years away and can be found at right ascension 05h 35m 24s and declination -05° 27’ 00”.

M43 (NGC 1982, De Mairan’s Nebula) – This bright nebula is next door (and practically part of) M42. It has a magnitude of 9.00 and an apparent size of 20.5 x 15.0 arcminutes. It is 1,400 light-years away from us and is located at right ascension 05h 36m 36s and declination -05° 16’ 00”.

M78 (NGC 2068) – This bright reflection nebula has a magnitude of 8.30 and an apparent size of 8.0 x 6.0 arcminutes. It is 1,600 light-years away and is at right ascension 05h 46m 42s and declination +00° 03’ 00”.

Barnard 33 (Horsehead Nebula) – This dark nebula is visible as the silhouette of a horse’s head against the background of emission nebula IC 434. Its apparent size is 6.0 x 4.0 arcminutes. The Horsehead Nebula is 1,600 light-years away at right ascension 05h 40m 44s and declination -02° 28’ 00”.

The horsehead nebula
The Horsehead Nebula (source)

Barnard’s Loop (Sharpless 2-276) – This emission nebula has a magnitude of 10.00 and a huge apparent size of 600.0 x 30.0 arcminutes. Spread over such a huge area, it is very faint for telescope work but a spectacular astrophotography target. It’s 1,600 light-years away and is at right ascension 05h 48m 00s and declination +01° 00’ 00”.

NGC 2023 – This bright nebula has a magnitude of 10.00 and an apparent size of 10.0 x 10.0 arcminutes. The nebula lies 1,533 light-years away from us at right ascension 5h 41m 36s and declination -02° 14’ 00”.

NGC 2024 (Sharpless 2-2777, Flame Nebula) – In the same region as NGC 2023, this emission nebula also has a magnitude of 10.00 but its apparent size is 30.0 x 30.0 arcminutes. It is 900 light-years away at right ascension 05h 41m 42s and declination -01° 52’ 00”.

NGC 2169 – This open cluster has a magnitude of 5.90 and an apparent size of 5.0 arcminutes. It is 3,600 light-years away at right ascension 06h 08m 24s and declination +13° 57’ 00”.

NGC 2174 (Monk Head Nebula) – This bright nebula has a magnitude of 7.59 and an apparent size of 40.0 x 30.0 arcminutes. It is 1,370 light-years away and is at right ascension 06h 09m 42s and declination +20° 30’ 00”.

Summary

Orion is a large constellation with many notable stars and deep sky objects. It’s the starting point for several star hops. Look south this winter to enjoy this constellation’s wonders.


Written by Tanya C. Forde