Finding Sigma Octantis

27 February 2019

We're always being asked how to get a good polar alignment on an equatorial mount.

There are several ways, and how you do it is going to be determined by what hardware and software you have, so I won't bore you with details (although you can ask us).

But the most important thing that helps is being able to locate the pole in binoculars. It's difficult, especially in the inner city, but with a bit of practice and perseverance (and insect repellent) you can find it, and then come back to it again.

Then, once you've got it in your sights, you'll know immediately where "roughly polar aligned" is, so you can get your mount set up quickly.

Even some experienced photographers think this is too hard for them. It's not!

The first big tip is don't start with your polar scope or telescope - those magnify too much. Start with low power binoculars.

My first photo shows you (best on a screen) how to get into the area from the Southern Cross.

The second photo I took last night, from my front garden in Kew. I've marked some stars and a few things for you to take note of.

The actual Pole is in the yellow circle.

The two triangles (one flat, one equilateral) two thirds of the way to the right are very good landmarks for you to look out for.

The red dotted line is the field of view of some 8x42 binoculars (I've modelled this one on the data for the Vortex Diamondback, but they're all very similar).

You'll notice that if you get the three Gamma Octantis triplet stars (marked as γ1 Oct, γ2 Oct and γ3 Oct) in the very edge of binocular field, you should be able to get most of the archery-bow-shaped asterism with Sigma (σ) Octantis in as well.

Remember that the whole sky revolves around the Pole. So my most useful tip is that if you imagine the Gammas are a really flat arrowhead, they point to Chi (χ) Octantiss, which might be a tiny bit more than one binocular field width away. Knowing how far it is in your binocular field will stop you overshooting.

Good hunting!