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DSC-60: Sigma Orionis – an easy triple that would get more attention if it wasn’t in such a great neighborhood!

This is a DSC-60 Project observation – for project details go here.
Sigma Orionis 05h 38m.7 -02° 36′ 4.0, 7.5,
12.9″,43″ 84°, 61°

Sometimes it doesn’t pay to be in such a good neighborhood – it’s too easy for folks to ignore you. even when, like Sigma Orionis, you’re a beautiful and easy triple. Well, a quadruple really, but the DSC list it as a triple and the fourth star can be difficult to dig out.  OK, it’s actually five stars, but the last one is next to impossible, so I don’t count it – but it’s why you see the primary referred to sometimes as “AB” rather than just “A.”  Sigma is just an easy hop away from the dazzling Trapezium, a quadruple that is so good – and so in reach of everyone – that I hardly think of the Trapezium as a multiple star. It seems to be in a class by itself.

But if you like the Trapezium, take a little trip up to the eastern end of Orion’s belt. The bright star is Alnitak, but a bit less than a degree to the southwest (PA 218) of it is Sigma. The two can fit in a low power eyepiece. John includes some nice charts and some other neighborhood highlights in his post here. You will be delighted with Sigma as an easy triple. You will be challenged, but pleased to see you can turn it into a quadruple.  And as I said,  don’t even think about that fifth star – there’s only a quarter of a second separation between it and the primary.  And while we’re on the subject there are really a couple more stars that go with the Trapezium, but they too are difficult – though not impossible – targets.

Meanwhile, Sigma is just fine as an easy triple – the three main stars are bright and the separations wide. I come to this star often, but my first try with the 60/360 was on the first night out with that small scope, February 14, 2011. Using a 7mm Nagler (51X)  I had a solid split of the three components listed in the Double Star Club – absolutely charming. The primary is a whitish blue, the star closest to it is a steely blue and the third star I see as yellowish. I could not see the fourth star, even though I know right where to look for it. I did see it easily a couple weeks later when using an 8-inch SCT and it can be dug out with smaller scopes.

But what strikes me here goes to the heart of why multiple stars are so much fun – they are so different from one another! Look at Sigma, then look at the Trapezium, and while you’re in the neighborhood, swing over to Beta Moncerotis. Three multiple stars giving you three distinctive looks – all different in the pattern they form with one another, in their colors, and in their different magnitudes and separations.!


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