Two big birds

The Constellations
This article features a pair of celestial birds going head-to-head. To find Cygnus, the Swan, and Aquila, the Eagle, start at Vega in Lyra, seen in last month’s article. The bright stars Vega, Deneb and Altair form a brilliant asterism known as the Summer Triangle.

Blue-white Deneb, which marks the swan’s tail, is the 19th brightest star in our skies. The point where the swan’s neck meets the wings you see another fairly bright star, named Sadr. Once you have Deneb and Sadr, you can trace out the two large triangular wings. From there, you should be able to follow the few dim neck stars to Alberio. Alberio is a beautiful double star, easily split in a small scope or steady binoculars. The colour difference is remarkable; put your instrument slightly out of focus and look directly at the stars to enhance the colours. It’s my current favourite double.

Altair, the Eagle’s eye, is the sky’s 12th brightest star. The eagle is a bit of a stick figure, even for a constellation, but easy to trace.

Sagitta, the Arrow, is small but surprisingly easy to find.

I have marked a few of the region’s telescopic treats on the map. M57, the Ring Nebula, and M27, the dumbbell, are planetary nebulae. M71 is a globular cluster.

The Milky Way
In June, we start to see the summer’s splendid Milky Way. Thin in Perseus, it spreads through Cassiopeia and is quite thick and rich when it reaches Cygnus. At Deneb, the Milky Way splits into two distinct channels, with a dark band between.

What produces the Milky Way’s pale glow? Why is it thin in Perseus, and thick half a sky away in Sagittarius? Why does it have dark patches and great rifts, as seen in Cygnus? The nature of the Milky Way remained a mystery, even after Galileo turned his small telescope on the Milky Way in 1610 and discovered that it is countless stars too small to see without aid. In 1750, Thomas Wright deduced, from the way the Milky Way forms a band around the sky, that we live in a great, flat disk of stars, and since it’s thinner in one area and thicker in another, that we live near the edge. The full story was uncovered only in the first half of the 20th century, with large telescopes and photography. We are looking through a disk of stars, as Wright said, but it has spiral arms, and enormous clouds of dust that hide any stars behind. What’s more, it’s just one of many separate galaxies.

Observing distant galaxies is a distinct pleasure for many amateur astronomers, but you should take every opportunity this summer to grab some binoculars and take in the nearest and most easily observed galaxy – our own Milky Way.