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Featured Deep Sky Objects
61 Cygni

Deep Sky Object Chart | Deneb & NGC 7000 | Albireo | Chi Cygni | Omicron 1 Cygni | Cygnus X-1 | M29 | M39 | NGC 6828 | NGC 7027 | Veil Nebula
61 Cygni is a fainter naked eye star about 5.5 degrees northeast of the eastern wing star (epsilon Cygni). A telescope actually shows two orangish stars, about as far apart as Jupiter's disk looks from Earth.

There are lots of the stars in Cygnus, so what's the big deal? Well, firstly, early observers could see that as the years went by, these two orbited one another - a true double star, and what's more they obeyed Newton's laws of gravitation, so we knew old Sir Isaac was on to a law of the universe, not just the solar system. The stars take about 700 years to finish a cycle, and they are separated by about three times the diameter of our solar system...not as close as they seem in the scope, and doubtless mail delivery is a hassle from one star to another.
Adding to the scientific bonus for early astronomers, the pair seemed to wobble slightly in the sky in a period of exactly one year; in 1838, German mathematician Freidrich Bessel figured out that this motion was the result of Earth orbiting the sun and offering us a slightly different angle on 61 Cygni compared to more distant stars. This first measurement of "parallax" gave a calculation of the stars' distance: 10 light years, very close to today's more precise estimate of 11.1. Compared to Deneb's 1600 light year distance, this is nothing, and it's why the motion of 61 Cygni is more obvious - they're quite close, in galactic terms (4th nearest among all naked eye visible stars). These stars are not supergiants like Deneb, but smaller, cooler suns like our own, and it's fun to imagine what it would be like to live on a planet which has two sun rises and two sunsets every day!

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There are lots of the stars in Cygnus, so what's the big deal? Well, firstly, early observers could see that as the years went by, these two orbited one another - a true double star, and what's more they obeyed Newton's laws of gravitation, so we knew old Sir Isaac was on to a law of the universe, not just the solar system. The stars take about 700 years to finish a cycle, and they are separated by about three times the diameter of our solar system...not as close as they seem in the scope, and doubtless mail delivery is a hassle from one star to another. Adding to the scientific bonus for early astronomers, the pair seemed to wobble slightly in the sky in a period of exactly one year; in 1838, German mathematician Freidrich Bessel figured out that this motion was the result of Earth orbiting the sun and offering us a slightly different angle on 61 Cygni compared to more distant stars. This first measurement of "parallax" gave a calculation of the stars' distance: 10 light years, very close to today's more precise estimate of 11.1. Compared to Deneb's 1600 light year distance, this is nothing, and it's why the motion of 61 Cygni is more obvious - they're quite close, in galactic terms (4th nearest among all naked eye visible stars). These stars are not supergiants like Deneb, but smaller, cooler suns like our own, and it's fun to imagine what it would be like to live on a planet which has two sun rises and two sunsets every day!

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