December Night Sky

One of the frustrating things about observing in a UK autumn is mist and fog. Those mild, sunny days that we have had recently under high pressure quickly yield to misty evenings that may obscure deep sky objects, and cause dewing problems. Planets are not so badly affected, but only Uranus, and Neptune if you are persistent (I finally managed to spot it last night from my back garden in Bath despite a nearby first quarter moon!),  are available.

But there are also double stars, and they can be enjoyed in pretty well any conditions that allow observing at all. The best example visible mid evening in December is Gamma Andromedae. It is easy enough to find as the westernmost of the 4 bright stars that make up the backbone of the constellation, starting with the top left star of the square of Pegasus. In any serious telescope you will see an orange primary with a blueish companion, making a lovely colour contrast. (This also makes it very useful for convincing doubters that stars have colours!). The companion star is itself a double, but the components are too close to be separated visually. A little further south is Gamma Arietis, another pleasing double, but no colour contrast this time as both components are whitish.

The map below shows where you can find each of these doubles. A little later in the evening, Gemini will come into view, with the first magnitude heavenly twins, Castor and Pollux. Castor is itself a very pleasing double, though again with no colour contrast. Heavenly twins can be as hard to distinguish as earthly ones, but I find Castor’s more northerly position the most reliable way of homing in on the right one!

Winter Double stars