ÎçÒ¹¸£Àû1000¼¯ºÏ

CYGNUS the swan is a beautiful constellation filled with plenty of interesting stars and deep-sky objects. It is visible this time of year almost anywhere in the world: in the northern hemisphere it sits high overhead throughout the night, while in the southern hemisphere it appears lower in the sky, towards the north, as soon as it gets dark, and sets a few hours later.

To find Cygnus, you can use a pattern of stars, or asterism, called the summer triangle, so named because it is directly overhead in the northern hemisphere during summer. In the northern hemisphere, look east when it is dark to see the three brightest stars making up a large triangle. Vega will shine highest in the sky, with Deneb, which is in Cygnus, to its left and Altair below. In the southern hemisphere, Altair will be highest, with Vega and Deneb closest to the horizon.

To find the rest of Cygnus, look between Deneb and the other stars of the summer triangle. Within them you will see four more bright stars making up a cross shape, sometimes called the northern cross. Deneb – which forms the tail of the swan – is at one end, while directly opposite, and in line with Vega and Altair, is a star called Albireo – the head of the swan. The rest of the cross, and the wings of the swan, stretches out in a line perpendicular to an imaginary line drawn between Deneb and Albireo.

Albireo is a double star, meaning it is made up of two stars. This makes it one of the loveliest stars to look at through a small telescope because you can easily see both stars: one larger and yellowy orange in colour and the other smaller with a blue-green hue. Technically, the brightest star is called Albireo and the other, which is about 390 light years away, is Beta Cygni B.

Cygnus is also a great constellation to look at through binoculars because its position along the Milky Way means there is plenty to spot. The stars 30 and 31 Cygni make up a double star that can be seen with binoculars, while there are a few visible open clusters of stars, including Messier 29, close to the centre of the swan.

There are historically important stars in Cygnus, too. In the 19th century, the star 61 Cygni was the first to have its distance from Earth measured by German astronomer Friedrich Wilhelm Bessel. He did this by measuring how the position of the star in the sky appeared at different points in Earth’s orbit around the sun. This was the first example of measuring interstellar distances using a technique called parallax, which is still important today.

It works on smaller scales, too. With one eye closed, extend your arm in front of you and make a thumbs up. Then, open your closed eye and shut the other: your thumb appears to move. This is because you are viewing it from your other eye.

For other projects visit newscientist.com/maker

Abigail Beall is a features editor at New Scientist and author of The Art of Urban Astronomy. Follow her @abbybeall