Getting to Know Orion: Stars, Nebulas, Meteors, Oh My!

We’ve reached the end of this little miniseries on the wonders of the sky in the vicinity of the popular constellation Orion the Hunter (here’s part 1, part 2, and part 3). While I could drag this out longer, there are other space stories coming up that I’m going to want to be blogging about (Artemis 2 anyone?), so I’ve decided to round up some of the more interesting facets of the Orion part of the sky that I have yet to cover and put them all together.

But have no fear! There’s still plenty of cool objects to gush about, from honkin’ huge stars to spectacular cosmic clouds, and I’ll even throw in a solid mention for the meteor shower named for this constellation just as the cherry on top.

Seeing Stars

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Obviously I’ve already covered several of Orion’s stars, namely the Belt stars of Alnitak, Alnilam, and Mintaka, and of one the Hunter’s shoulders, the red supergiant Betelgeuse. That’s over half of the big, bright stars making up the main part of the constellation. But what about those remaining ones?

I’m talking about the other shoulder star, Bellatrix, and Orion’s two knees, Rigel and Saiph. Together with Betelgeuse they make up the Hunter’s frame, with the Belt marking his middle. Bellatrix is the rightmost (or westernmost) shoulder, above and to the right of the Belt, Rigel is the westernmost knee below and to the right of the Belt, while Saiph is the easternmost knee, below and to the left of the Belt. 

Let’s begin with Rigel which, as the brightest star in Orion, is the most easily visible of the three (not that any of them are faint). The star we think of as Rigel is actually the brightest of a four-star system about a thousand light years away. The blue supergiant is enormous, over 70 times the Sun’s radius with a surface temperature well over 20,000 F (11,000 C).

Not far from this blue supergiant (technically Rigel A) is a trinary system. In this system two stars orbit each other every ten days while the third star orbits the inner two every 63 years. This triple star system and Rigel A then orbit around a common center of gravity once every 24,000 years. It’s complex and rather spread out, but the fact that they are all gravitationally bound to each other does mean they are considered to belong to a single system, though when you look at Rigel in the sky the supergiant is the vast majority of the light you’re seeing.

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Then there’s Bellatrix, a star that nobody knew the name of until it was adopted as one of the characters in the Harry Potter franchise. The name, meaning “female warrior” is undeniably cool, and the star outburns Rigel A with a surface temp of nearly 40,000 F (22,200 C). Despite burning so hot, at less than seven times the Sun’s radius Bellatrix is much smaller than Rigel (though obviously still way bigger than our Sun).

Interestingly, like Betelgeuse this star may also be holding out on us with a hidden companion. There has been evidence that Bellatrix is concealing within its bright light a small, dim, companion star. But if it’s there it’s so small and dim that we have yet to be able to conclusively pick it out from Bellatrix’s glare.

Which leaves us with Saiph. Of the seven stars in Orion I have called out by name over this miniseries, only the Belt star Mintaka appears dimmer than Saiph. Being only pretty bright among the super bright stars of this constellation and having no franchise characters named for it, Saiph is often overlooked, even among astronomical types. Full confession: it took quite a while into my astronomy career before I bothered to look up and remember Saiph’s name.

Which is unfair because if you lined up those seven bright Orion stars next to each other Saiph would outshine Betelgeuse and Bellatrix as well as Mintaka (it would be about equal to Alnitak, though Alnilam and especially Rigel would outshine them all). Saiph is a baby, less than six million years old, and burning even hotter than Bellatrix with a surface temp of nearly 46,000 F (25,500 C)! It puts the brilliance of the rest of the constellation into perspective when you think that this is the star getting ignored!

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Cloudy with a Chance of Stars

We’ve already covered numerous nebulas in this miniseries: the Orion Nebula, of course, but also the Flame and Horsehead Nebulas. But wait, there’s more! In fact, there are several more nebulosities to be found with Orion, too many to call them all out individually. So I’ll just pick out a few of my personal favorites, starting with Messier 78.

Why do I like this one in particular? It’s just pretty is all! It is a star-forming region, like the Orion Nebula, but far more enshrouded with dark dust lanes that obscure what lies within it. Two bright stars are lighting up some slightly less dusty parts of this cloud, leading to a visually pleasing dichotomy between the parts shining with reflected brightness and the dark twists of the surrounding dust lanes. It’s just pretty, and it’s earned the nickname “The Casper the Friendly Ghost Nebula” and who wouldn’t love that?

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In a similar vein, just to the east of Rigel one can find a nebula that gets called out every Halloween for being a spooky sky object, the Witch Head Nebula. This is a possible supernova remnant close enough to Rigel in space to be glowing with reflected light from the massive star. And, if you flip it upside down, it does indeed appear to be a profile of a stereotypically depicted witch character a la Margaret Hamilton as the Wicked Witch in “The Wizard of Oz”.

Far fainter but far more extensive is the nebulosity known as Barnard’s Loop. This giant arc of clouds is something around 360 light years long, an almost perfect semicircle beginning in what would be the chest region of Orion the Hunter, looping right around the Belt and the Sword, curling just above Saiph and coming to a halt right before it would appear to touch Rigel (meaning Rigel appears to be bracketed by the Witch Head Nebula on one side and the end of Barnard’s Loop on the other in deep pictures of this sky region). 

All of these nebulas are considered to be a part of a truly gigantic structure many hundreds of light years across known as the Orion molecular cloud complex. It stretches from what would be the Hunter’s head all the way to his feet and is made up of a number of different cloudy pieces. These include, obviously, a number of star-forming regions as well as at least a few possible supernova remnants and some clouds that are just sitting there minding their own business. It’s a very busy part of the sky!

Whence the Orionids?

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I feel like it’s weird for me to have a whole miniseries about the Orion region of the sky and not mention the Orionid meteor shower, even though it doesn’t actually have anything to do with the constellation or this region of deep space. Things just happen to line up well for the meteor shower to steal the constellation’s name. 

Meteor showers are named for the constellation from which they appear to emanate from our point of view here on Earth. Why that happens is something I’ll have to go into in more detail in a different post, but for now let’s just say that the meteor shower we know as the Orionids is called that because these meteors appear to have the Orion area of the sky as their origin point.

To be clear again: they are not coming from anything that is part of the constellation Orion. They are actually bits of debris left behind by Halley’s Comet that Earth plows through every mid-to-late October, providing us with this annual shower. But it does share a name with the constellation so I figured I should at least mention it.

Just Look Up

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What a piece of sky this constellation takes up! So many newborn stars! So many bright stars! So many, many nebulas! Stellar birthplaces and a harbinger of fiery supernova star death! All in one single constellation!

The thing is there are many patches of sky that can claim similar adornments. It’s just that the ones in Orion are close enough to us that it’s easier than normal to spot them and that handy Belt trio of stars makes the entire constellation one of the easiest to find in the sky.

So whether you’re hunting with a telescope, scanning the sky with binoculars, or just taking a moment to gaze up at the cosmos, this is the time of year to hunt down the Hunter Orion. Look for his sparkling belt, take in his dying shoulder star, wonder at the incredible powers of creation being mustered in the sword.

Or just, you know, enjoy looking up at the sky. That’s also a very cool thing to do. The important thing is to just look up.