First Light Guides #19: Great Orion Nebula

The object: Messier 42

A detailed guide to finding / observing the nebula in Orion

First Light Guide 19 graphicFirst Light Guides #19 is a detailed written and video reference to finding and observing the nebula Messier 42, sometimes called the Great Orion Nebula, that is located in the constellation of Orion. This guide is ideal for beginners, but many advanced amateur astronomers may find it useful. It is designed to help you locate this nebula with almost any telescope. There is a video to using a magnified finderscope, red dot finder, or setting circles along written tips on observing Messier 42.

Visitors who are new to this site may wish to get started here, while more advanced observers can search the First Light Guides by constellation, or by right ascension


Find Messier 42 in the sky

Messier 42 is perhaps the single best nebula to observe in the entire night sky, especially for northern hemisphere observers. It is located within our Milky Way galaxy, and is a giant cloudy of gas that is in the process of forming stars that will one day become an open cluster in that part of the sky. The integrated magnitude of this nebula is very bright - around 4th magnitude - and therefore this glowing cloud of gas is not hard to find or see from most anywhere, and with most any telescope. However, larger telescopes will show more of it, and darker skies will help as well. 

If you have a magnified finderscope on your telescope, start here to find Messier 42:

If you have a red dot finder on your telescope, start here to find Messier 42:


Observing tips:

The heart of Messier 42 is easy to see - it is very bright, and in it's center are 4 stars that were initially named as Theta Orionis. But the multiple nature of these stars was later revealed, so there are A, B, C and D components that most any modern telescope can split and allow the observer to see. These are called the Trapezium. Two more difficult components, E and F, require larger telescopes and more steady skies. 

For the nebula itself, observers spend a lifetime viewing it an teasing out detail. Here are a few tips to get more from seeing this fantastic object:

  1. Use a larger telescope if possible. More light collected from larger aperture will reveal more.
  2. Although observing it whenever it is clear is helpful, observing when the skies are more transparent - that is, free from dust and humidity - will reveal more, and for some observers, some color or more color.
  3. Speaking of color, younger eyes will see lots of it. Older observers may see less, or none at all. Larger aperture helps. 
  4. To try to see color, if you are able, intentionally do not dark adapt. Dark adaptation means the cones of human eyes, that perceive color, are not working. To force the cones to work, try shining a flashlight into your eyes, then observe the nebula. Again, larger aperture helps because the greater light gathering brightens the image. 
  5. Try using averted vision. The fainter wisps of the nebula are revealed in lower light conditions; this is where being dark adapted helps. Averted vision is the process of concentrating on a specific area to observe, but then looking slightly away from that area. This causes the rods of the human eye, which are outside of the center of the field of vision, to perceive light. 

The Orion Nebula is a fascinating, complex object that is best observed over the course of many nights, and even years. 

Useful filter(s): An Ultra High Contrast (narrow band) light pollution filter and/or an O-III filter can both help enhance the visibility of structure in this nebula. Each will bring out slightly differing views, so one is not necessarily recommended over the other, as each enhances it substantially. If a viewer only has a budget to choose one, get a UHC light pollution filter first. 

What should I see?

Below is an approximate view of Messier 42 and the surrounding stars as seen with a 70mm telescope at 38x magnification, and a 1.40 degree telescopic field of view.  

M42 graphic at 38x in 1.40 FOV

Details of Messier 42

Type: Emission nebula

Distance: 1,344 light years

Angular size: Over 1 degree

Apparent magnitude: 4.0 (integrated)

Right ascension: 05h 35m 17.3s

Declination: -05° 23′ 28










Because telescopes and observers are all different, here are some alternate sketched/drawn views of Messier 42:

Jeremy Perez at 38x in 8" reflector

Jeremy Perez at 38x in 6" reflector

Michael Vlasov at 80x in 8" reflector

Kiminori Ikebe at 30x using 30x125 binoculars

Mark Seibold in 10" Newtonian, comparing dark skies, suburban, and urban views


The constellation: Orion

General information can be found here about Orion the Hunter, where Messier 42 is located.  This will help you know where to find the constellation in the sky and be able to locate and identify its brightest stars.

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Name of constellation: Orion

Abbreviation: Ori

Genetive form: Orionis

Common names: The Hunter

Associated asterisms: Belt stars (three bright stars that form a "belt" across the hunter's midsection)

Original 48 of Ptolemy: Yes

Area by size: 594 square degrees

Relative size: 26 out of 88 (Cassiopeia is next larger, and Cepheus is next smaller)

First Light Guides objects: Messier 42, Delta Orionis, NGC1981, NGC2169, Struve 747, Sigma Orionis

Brightest stars, in order of magnitude 

First lists the Bayer designation, then the "traditional" star name (often Arabic, but not always - see each star's notes for details). Graphic shows the constellation on the meridian while facing south from the northern hemisphere.

  • β (beta) Orionis (Rigel) magnitude 0.18, the 7th brightest star in the sky. There is not a traditional name precisely for Rigel, but one of them that may have been attributed to it riǧl al-ǧabbār came from Arabic which meant, "Foot of the Great One."
  • α (alpha) Orionis (Betelgeuse) magnitude 0.43, the 9th brightest star in the sky. The word itself does not mean anything in any prior language, and was often spelled differently in many texts. Paul Kunitzsch, Professor of Arabic Studies at the University of Munich has proposed that the full name is a corruption of the Arabic يد الجوزاء Yad al-Jauzā' meaning "the Hand of al-Jauzā'"i.e., Orion.
  • γ (gamma) Orionis (Bellatrix) magnitude 1.62, the 27th brightest star in the sky. Traditional name comes from Latin and means "female warrior" which explains it sometimes being referred to as the "Amazon star."
  • ε (epsilon) Orionis  (Alnilam) magnitude 1.68, the 30th brightest star in the sky. It's name comes from Arabic which means "string of pearls."
  •  ζ (zeta) Orionis (Alnitak) magnitude 1.70, the 31st brightest star in the sky. It's traditional name means "the girdle."
  • κ (kappa) Orionis (Saiph) magnitude 2.05, the 52nd brightest star in the sky. The traditional name is from the Arabic saif al jabbar, ' which means "Sword of the Giant." This name was originally applied to the star now known as Eta Orionis.
  • δ (delta) Orionis (Mintaka) magnitude 2.21, is the 69th brightest star in the sky. It's traditional name is derived from Arabic, and means, "The Giant's belt."
  • ι (iota) Orionis magnitude 2.75, and is 1,325 light years distant.
  • π 3 (pi 3) Orionis magnitude 3.19, and is 26 light years distant.
  • η (eta) Orionis magnitude 3.35, and is 901 light years distant.