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Scorpius, The Constellation of Winter

Each time of the year has a recognisable constellation that seems to dominate the night sky. In summer it is Orion, with its easy to spot belt of three stars. It’s hard to pick a constellation for each season that seems more important or recognisable than the others so my criteria for saying that Scorpius is the constellation of winter is pretty loose, though it is the zenith constellation for New Zealand. In Autumn I’d pick Canis Major as this seems to be the constellation that dominates the sky with Sirius being nice and high, and being the brightest star in the night sky, it is hard to miss. But now as winter is here it’s Scorpius that is the prominent constellation and it heralds the rising of the galactic centre.

Our video on how to find Scorpius

So why Scorpius? It’s probably because of its distinctive shape of curved stars that bend around towards the red star of Antares, that star most often mistaken for Mars due to its colour. There’s plenty of stories about Scorpius and many cultures around the world organise the night sky to include this grouping of stars and assign it different names. To me, the real story is in the stars themselves.

The Constellation of Scorpius in its IAU boundary

The way constellations go is that the stars are named based on their brightness, so the brightest star in the constellation carries an ‘alpha’ then ‘beta’ and so on down to the dimmest star. Of course there’s plenty of different versions of which stars make up a constellation so fortunately the IAU introduced constellation boundaries, which are the brown dashed boxes in the above image. Most stars have many different names and as almost all cultures had names for the various stars it can be easy to use a name that someone else doesn’t recognise. Fortunately astronomers, being the practical people they, came up with a solution for that, they assigned catalog numbers to each of the stars depending on the catalog. So for the red supergiant, commonly known as Anatres, is 80763 in the Hipparchus catalog or 148478 in Henry Draper’s catalog and is 6134 in the Yale Catalogue of Bright Stars.

To help you find your way around Scorpius I’ve helpfully labelled each star by its Hipparchus Catalog number. The colours are relative to the star’s colour indices.

Now that we’ve gotten over any star naming concerns and have a standard we can use across the galaxy, let’s talk about 80763, or as mentioned above , Antares (Rehua). This star is amazing, it is a huge red supergiant, you would need to line up nearly 500 of our Sun’s to get an idea of the size of this star. If it was in our Solar System, the edge of the star would be somewhere between Mars and Jupiter, we’d be well within the star and sizzling away. The other two reddish stars in the diagram are 82396 and 82729. These are both K class stars which means they should be a bit more yellow as they are hotter than the the relatively cool M class, Antares.

82396 or Epsilon Scorpii is the closest star to us in Scorpius at about 63 light years and 82729, Zeta Scorpii, is the third closest at 132 light years. The most distant star in Scorpius is 87073 or Iota Scorpii at 1900 light years. This massive range in the distance of these stars demonstrates that the constellations only make patterns we ascribe to them from our line of sight to the stars, they seldom mean anything more that. Another example of this is the blue star 82514 or Mu Scorpii. If you look through binoculars you will see two blue stars very close together but they are actually hundreds of light years apart.

The four stars in the head of the Scorpion, 78104, 78265, 78401 and 78820 are all reasonably close to each other along with 81266. If we exclude 78820 (Graffias or Beta Scorpii, though not the second brightest star in Scorpius) then the other four stars are all within about 50 light years of each other, which is quite close in stellar terms.

This is a ‘fly around’ of Scorpius to demonstrate how far the stars are spread out.

The above ‘fly around’ of the constellation shows just how spread out the stars are and it also indicates the relative sizes of the stars compared to each other. This constellation is a marker that we often use to help find other interesting things in the night sky so it’s well worth getting familiar with.

CategoriesAstronomy