A Winter Night’s Sojourn in Orion’s Belt

Orion's Belt is a magnetic sight on February nights. Take the bait and revel in a bounty of double and multiple stars, nebulae, and more.

Belt bounty

Orion's Belt is a magnetic sight on February nights. It's home to an assortment of double stars and nebulae. The Flame Nebula (left, above star) and IC 434 and the Horsehead Nebula (left, below star) are faintly visible in this image.
Bob King

Orion's Belt, the most recognizable starry asterism in the sky, stands front and center at 8 p.m. on February evenings. Visible from virtually everywhere on Earth, the belt is everything: a naked-eye treasure, a handsome binocular sight aglitter with dozens of stars, and a rich hunting ground for telescope users.

The most famous dark nebula in the sky, the Horsehead, resides here, as do nine other nebulae, a unique star cluster, and the remarkable multiple star Sigma (σ) Orionis. Plus, one of the Belt stars is a double and the other a triple. The only thing the asterism lacks is a bright nebula or star cluster, but you can resolve that deficiency by descending 4° south to the Orion Nebula and friends.

Although the following observations were made with a 15-inch (37-cm) Dobsonian reflector, I'll note when objects can be seen in smaller instruments. Let's start with several fine double and multiple stars in order of increasing right ascension (RA). STF refers to a double star in the Friedrich Struve catalog:

  • 31 Orionis: Beautiful orange primary paired with a delicate 11th-magnitude companion 12.7″ almost due east. The primary's color combined with the imbalance in magnitudes makes this a striking pair.
  • Delta (δ) Orionis (Mintaka): The westernmost star in the Belt, Mintaka appears searingly white at low power. It's joined by a bright 6.5-magnitude companion 53″ due north. If you like sapphires, you'll love Mintaka.
  • STF 734: A nice triple, though rough seeing for much of the winter has squelched my attempts at splitting the 7th-magnitude primary's 8.5-magnitude companion 1.5″ to the north. The third star, however, is very easy, shining 30″ to the west-southwest at magnitude 8.3.
  • HV 118: Magnitudes 6 and 10 with the companion 28″ almost due west.
  • STF 751: Magnitudes 8 and 9, separation 15″. Easy, low-power double 13′ northwest of the central Belt star, Alnilam.
Stellar Multiplication

Sigma Orionis (center) and the triple star Struve 761 will add a lot of sparkle to your wintertime observing. The inset shows the stars' labels and separations. North is up.
Photo: Peter Wienneroither / Inset: S&T

  • Sigma (σ) Orionis: A stunning quadruple with four stars like an elaborate earring easily resolved at 64×. The fainter triple star Struve 761 lies just 3.5′ to the northwest, making these side-by-side multiple stars a must-see in telescopes 3-inches and up. Stick to the lowest power required to split them to preserve their crisp, fiery beauty.
  • Zeta (ζ) Orionis (Alnitak): The easternmost star in the Belt. The pure white, brilliant 1.9-magnitude primary dominates its dim 9.9-magnitude companion 58″ to the north-northeast. The pair resembles Mintaka but with a fainter secondary star. Increase the magnification to 200× or higher and you'll spy the magnitude-3.7 companion just 2.2″ southeast (P.A. 166°) of the primary, elevating Zeta from double to triple star status. A 4-inch scope should be up to the task on nights of good seeing.
Loosening up the Belt

Use this map of Orion's Belt to find our featured double stars and deep-sky objects. Click for a larger version you can print and use at the telescope.
Stellarium, with additions by the author

Orion is home to the Orion Molecular Cloud Complex, an extensive group of bright and dark nebulae of which the Orion Nebula is only the brightest manifestation. Located between 1,500 and 1,600 light-years away and spanning about 25°, the cloud is hundreds of light-years across and home to thousands of new and "in utero" stars. Some of these suns light up patches of dust through reflection, others excite gases to fluoresce. We'll examine a variety of these clouds (and a lone star cluster) located within 1° of the Belt:

  • NGC 2024 (Flame Nebula): Although listed as an emission nebula and seemingly a great candidate for enhancement with an O III filter, I discovered to my surprise that the view was much better without a filter. Either way, you have to deal with light trespass from nearby Zeta Ori. Use a medium magnifications of around 100×–125× both to darken the sky and better keep Zeta out of the field view. With this setup, the amount of detail visible was amazing. A prominent dark rift "rips" the nebula in two, with smaller dark rifts chopping up the eastern half of the mass. Viewed south up, NGC 2024 resembles the Greek letter pi (π). (Dimensions: 30′ x 30′, Type: Emission)
Equine excellence

This amazing view of the Horsehead Nebula was taken in infrared light in 2013 by the Hubble Space Telescope. The nebula is backlit by the light from the nearby multiple star, Sigma Orionis.
NASA / ESA

  • IC 434 and the Horsehead Nebula (B33): IC 434 is the faint, diffuse emission nebula that provides the luminous backdrop for the shadowy Horsehead. The Horsehead was invisible without a nebular filter and, despite very dark skies, extremely difficult to pick out with the O III. But the hundred bucks I spent for an H-beta filter was well spent. Using a 142× eyepiece with the filter in place, the Horsehead appears surprisingly large (8′ × 6′ across) and opaque. With averted vision I could trace the neck and the head, and occasionally could tell what direction the nose pointed (north). Still, the Horsehead is vague and requires dark skies (you won't see it if you can't see the winter Milky Way) and averted vision.
    Often overlooked

    NGC 2023 reveals texture and dark nebulae "biting" into its periphery at higher magnifications and with use of averted vision.
    Hunter Wilson

    When using an H-beta filter, allow time for your eyes to adapt to the extra-dark field of view. Observers with telescopes as small as 6-inches have dug out the Horsehead with an H-beta under dark skies, so give it a try! (IC 434 dimensions: 60′ × 10′, Type: Emission; B33 dimensions: 8′ × 6′, Type: Dark nebula)

  • NGC 2023: Bright, diffuse emission-reflection nebula centered on a 7.6-magnitude star. Very easy to see with and without nebular filters, appearing like a luminous fog with a star shining through. At 124× without a filter the nebula was extended north-south with subtle variations in light and hints of dark mottling around the edges from encroaching dark nebulae. (Dimensions: 10′ × 10′, Type: Emission and Reflection)
    Realm of the nebulae

    The region around Zeta Orionis (above center) is replete with nebulae and double stars, including the patchy Flame Nebula (NGC 2024, left of Zeta), the pink curtain of IC 434 notched by the dark Horsehead Nebula, and side-by-side nebulae, IC 435 and NGC 2023, located above and to the left of the Horsehead. North is up.
    Miroslav Horvat

  • IC 435: This nebula is very easy to spot just 0.5° east of brighter IC 2023 and centered on an 8th-magnitude star. It's a little fainter than IC 2023 and only about half as large. (Dimensions: 4′ × 3′, Type: Reflection)
  • IC 432: This largish, faint reflection nebula extends north and south of a 6.5-magnitude star. Some texture was seen. (Dimensions: 8′ × 4′, Type: Reflection)
Ghost eyes

The reflection nebulae IC 432 (left) and IC 431 make a pair of fuzzy eyes north-northwest of Alnitak. North is up.
Rick Johnson

  • IC 431: A small, fairly dense ball of nebulosity centered on a 7.5-magnitude star. (Dimensions: 5′ × 3′, Type: Reflection)
  • IC 426: A dim but obvious haze extending east and north of a pair of stars with magnitudes of 8.6 and 10.7. (Dimensions: 7′ × 7′, Type: Reflection)
  • IC 424: Another small reflection nebula. Despite my best efforts, I could not confirm seeing it. (Dimensions: 2′ × 2′, Type: Reflection)
  • IC 423: A large, diffuse, faint, and vague patch, like frosty breath on the verge of dissipation. Partially fills the southern half of a rectangular figure of stars. No condensation and no obvious stars associated with the nebula. (Dimensions = 6′ × 4′, Type: Reflection)
  • Berkeley 20: This small patch of haze looks exactly like a faint comet at 64×. But using 224× I could make out four ~14.5-magnitude stars poking out of the mist. The cluster lies immediately west of a magnitude 11 foreground star. Be 20 is one of the most ancient open star clusters known with an age around 6 billion years. It's also one of the most distant — more than 27,000 light-years away. No wonder it's so faint! Photo here. (Diameter: 2′, approx. 20 stars total)

10 thoughts on “A Winter Night’s Sojourn in Orion’s Belt

  1. Walter ClaytonWalter Clayton

    Bob!

    Thank you for the map of Sigma Ori!

    I use the “C” star to test sky conditions. If I can see it at low power, then, it’s a good night. But, I have never been able to find a map that labels the stars in the system to tell me that “C” is “C”. It doesn’t appear on star charts normally (too close to the AB pair?) and in photos, it’s always washed out (definitely too close to the AB pair).

    Really good article! I hope to get a chance to put it to use this weekend (if it doesn’t rain).

    Thanks Again!

  2. Tom-Reiland

    Bob, Thanks for another informative article. It’s been a while since I have been able to observe the Horsehead Nebula. I used LP filters to enhance my views of it many years ago. At locations with dark sky conditions, it’s not too difficult to spot. I observed with it my 8″ f/5 in the 1980s and later with my 16″ Dob in the 1990s and the 21″ at Wagman Observatory up until about 5 years ago. Is your H-Beta filter an 1.25″ diameter that you bought for $100? I use 2″ Explore Scientific eyepieces and I will probably order their 2″ H-Beta for $150. I also enjoy observing the multiple stars Sigma Orionis and Struve 761. There are many fine objects near the Orion Nebula that observers often miss. The Open Cluster, NGC 1981 reminds me of a small pagoda and it’s an easy binocular object.

    1. Bob KingBob King Post author

      Hi Tom,
      I use a Lumicon 1.25-inch H-beta filter. Wish I had the 2-inch version for some of the wider-field objects. Speaking of which, have you ever used it on the Orion Nebula? The view is quite different from what you see without a filter or with an OIII or UHC.

      1. Tom-Reiland

        Bob, I haven’t ordered the H-beta filter yet, but when I get it I’ll give it a try. I get some spectacular views of the Orion Nebula with the 2″ O III filter on the 20 mm, 9 mm and 5.5 mm Explore Scientific 100 deg FOV eyepieces. The detail is amazing at 462X, especially in the region of the Trapezium. Though the Horsehead Nebula is the dark nebula that observers try to spot, the dark lane that you mentioned cutting through NGC 2024 is much easier to see and can be viewed without a filter. I keep hoping for some clear nights, but this February has been awful. I’ve only spent one night at Wagman Obs so far. I did see the SN in NGC 3941that’s about 12.5 mag on Monday night. Here’s hoping for a clearing very soon.

    1. Bob KingBob King Post author

      Thanks, Frank. Never heard of the North Arrow before. Yet another way to find north. I bet you could come up with additional north-pointing alignments for other seasons using other prominent stars.

      1. Frank-ReedNavigation.comFrank-ReedNavigation.com

        And it’s not just north! 🙂 The inclination of your thumb (relative to the horizontal plane) shows your approximate latitude, much like the gnomon of a sundial. For other star groupings that work the same way, there are none so bright and near the celestial equator. But there are a couple that are faint and can serve when Orion is hiding. In the (northern) summer sky there’s an asterism in Ophiuchus that I call the “sleeping rabbit” (runs from 70 Oph to beta Oph), but I’ll leave that for another time. Another excellent case is the water jar of Aquarius, which is aligned right along the equator and rather close to the First Point of Aries, too:
        http://fer3.com/arc/m2.aspx/g38306
        One can use the same trick: aim your hand at the water jar, this time perpendicular to the neck of the jar, and then your thumb points north and has an inclination equal to your latitude. Like the more prominent “Orion North Arrow”, this works anywhere on the globe –anywhere, that is, where there’s little light pollution and the skies are dark enough to see the fainter stars of Aquarius.

  3. Fabrice MoratFabrice Morat

    Hello Bob,
    In one of your thought above, you’ve said an important fact : M42 is fantastic with HBêta filter, it brings new informations on this nebula. When you draw, additional gaseous extensions become obvious mainly on the outside wings which close again the great bubble. And of course, this filter is a must on M43.
    Fabrice M.

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