Top 10 Best Double Stars to Observe in Autumn

Top 10 Best Double Stars to Observe in Autumn

Alpha Capricorni.jpg

This autumn, why not take advantage of the earlier sunsets and longer nights to get acquainted with some double stars? Double stars occur when two stars appear very close to each other in the night sky. This can simply be because they lie in the same direction, though they may actually be at vastly different distances from us. But some are in a binary star system, which means that they are gravitationally connected to each other. Binary stars (and also systems with three or more members) are in fact quite common. They can also be gorgeous to look at! Here are ten of the best to look out for:

1. Albireo

This lies in the constellation Cygnus, can be seen with a small telescope; it marks the head of the swan. The two stars which make up the double are different in colour, one being bluey-green, the other amber. It's a beautiful sight. It is the star marked with the arrow on the map below.

Position beta Cyg Alberio.png

2. Epsilon Lyrae

This star system is sometimes called the 'double double'. It lies in Lyra, close to the bright star Vega. It is possible to make out a binary star with binoculars, but with greater magnification, it can be seen that the two stars are in fact four. you can find it marked as star 4.6 on the chart below, not far from the bright star, Vega.


3. Polaris, the Pole Star 

Not many people realise that Polaris, one of the most instantly recognisable stars in the northern sky is actually a double star, although the companion star is much fainter, so needs a good telescope to be visible.

Polaris system.jpg

4. Mintaka 

Is easy to locate, as it is the westernmost of the three bright stars making up Orion's belt. It is actually a complex multiple system, but can be seen with a small telescope as a binary star with one star much brighter than the other. Mintaka is the star labelled 2.2 on Orion's belt


Alpha Capricorni.jpg

5. Alpha Capricorni

This double star in the Capricorn constellation was known to the mediaeval Arab astronomers, who called it Algiedi, the billy goat. It is bright enough to be seen with the naked eye on a dark night.

6. Epsilon Pegasi, known as the 'pendulum star'

This double star forms the 'nose' of the Pegasus constellation. There's an optical illusion associated with this double star, noted many years ago by the famous astronomer Sir John Herschel; if the telescope is moved whilst the double star is being observed, the fainter star seems to swing relative to the brighter one. The brighter star often appears as bright orange in colour. The star is otherwise known as Enif.

7. Gamma Delphini

In the constellation Delphinus, the dolphin. This one is bright enough to be seen with a small telescope as a pair of warm golden stars , and it forms the dolphin's snout. It is the star labelled 4.3 on the chart below


8. Eta Cassiopeiae

This one needs a good telescope to be seen properly, but the colours are worth looking out for - they appear as bright yellow and red. This double star is in the constellation Cassiopeia, which is one of the most distinctive features of the autumn sky. This binary is otherwise known as Achird. 

9. Zeta Aquarii 

Found in Aquarius, where it forms part of the 'water jar'. This one is difficult to see without a good telescope, but it has a lovely clear blue-white colour. The gap between the two component stars is slowly widening.

10. Gamma Arietis

Located in Aries is bright enough to be seen with the naked eye, although the stars are close together and a telescope will help to resolve them. Then they appear as 'cat's eyes', two white spots of nearly equal intensity. This is another double star with a history - Robert Hooke first realised that it was two stars rather than one in 1664.

There are plenty more double stars in the autumn sky, and these are just some of the most distinctive. They are beautiful to look at and fascinating to study. Let's hope for some clear skies this autumn!

Find more on: Observing the Night Sky

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