5.2 KiB
| name | created_by | created_date | updated_by | updated_date |
|---|---|---|---|---|
| Cygnus | skybber | 2021-06-19 08:02:54.697503 | skybber | 2022-02-11 18:36:31.714709 |
The most prominent summer constellation of the richest region of the Milky Way in the Northern Hemisphere. The constellation is very striking and is sometimes called the Northern Cross because of its shape (it is made up of stars, the centre of which is marked by the star γ Cygni, with the star Deneb at the apex and the famous double star Albireo at the base. When the Swan is in the east, the cross lies on the left side. Only as it moves westward, sometime around Christmas, does the cross gradually rise. The constellation includes a large number of individual objects, both pretty to look at and astronomically interesting. Among the binaries, Albireo and 61 Cygni are particularly well known, the North American emission nebula, which with luck can be detected in small binocular, and above all the jewel of the whole sky, the Algal Nebula, which, together with the Crab Nebula, is the best observable remnant of a supernova explosion. There are also a large number of planetary nebulae and open clusters in the constellation.
The Swan contains arguably the most visually beautiful part of the northern Milky Way. The Great Rift here, with its sharp boundaries with the starry clouds, exhibits high contrast. The most striking cloud (by far the brightest part of the Milky Way north of the celestial equator) extends in a westerly direction all the way from Albireo to the γ Cygni region and is elongated in shape. It extends about two degrees to the east of the conjunction of these two stars, and a degree farther to the west. First notice that it has a different brightness than the Cloud in the Shield - it is not as hazy and is more of a fluffy white color. In the binocular, there is a very high density of stars visible in this region. The western half of the cloud contains a very bright circular brightening around Albireo, this is the most striking formation ever in this part. The eastern half of the cloud is exceptional because of the abundant excess of stars of 6mag to 10mag brightness and there is a second brightening which includes a string of bright stars 28, 36, 40 Cygni and others. In addition, there is a system of dark nebulae throughout the cloud, the most striking of which is Fish in a Bowl (Barnard 144), in the vicinity of the star η Cygni. It takes the form of a slightly curled oval in the shape of the letter S. When we look into this region, we are actually looking along the spiral arm of our Galaxy, the Orion arm. Its edge curves toward the center in the Swan, while on the other side of the sky, in the Ship's Back and in the constellation Sail, it points away from the center.
A very interesting region is that around the star Deneb. The Great Rift ends here, the two main streams of the Milky Way join each other in a rather complicated way, and the Milky Way itself continues on with only one branch. The dark region centred roughly between Deneb and Gamma Cygni is called the Northern Coal Sack (LDN 896). To the east of it is a conspicuous star cloud that lies roughly in the region between the stars ξ, 57, 59 and 68 Cygni. It includes the well-known emission nebula North America. A long and narrow, but striking black rift cuts into the cloud from the north (from the α - η Cephei junction). It includes a very dark, oval-shaped region four to six degrees wide (Le Gentil 3), visually perhaps even darker than the sky itself, and containing not a single star visible to the naked eye. It is indeed black as coal and looks like a hole in the sky. After the Southern Cross Coal Sack and the Hadonous Pipe, it is perhaps the easiest dark nebula to observe in the sky. Yet in excellent viewing spots it does not disappear from the sky even with a ten-day-old Moon, especially if the atmosphere is so clear that scattering of moonlight in the atmosphere is minimal and there is no more light pollution.
The dark nebula continues in the form of a narrow section further on (Funnel nebula - Chimney) less distinctly, but uniformly with a constant width of one degree across the star ρ Cygni crossing the Milky Way, and at the other edge it passes smoothly into its surroundings. The optical binary ω Cygni is visible as a solitary hazy spot above Deneb. About four degrees east of Deneb, you can try to see an inconspicuous half-degree fog spot, in this case the open cluster M39, under good conditions. This is the centre of a small local brightening, located in the western half of another white star cloud. This is oblong in shape and on the other side extends to the northeastern limits of the constellation of the Lizard. It is perhaps comparable in size and brightness to the one in the western part of the Swan (there is no more conspicuous formation further out). Its brightness is uneven at first sight. The first conspicuous oval-shaped dark spot, Barnard 168 (Dark Cigar), in which no stars are visible to the naked eye, is four degrees slightly southeast just off M39. It has sharp edges and contrasts with its surroundings - a truly vast cloud of dusty material that prevents us from seeing into the more distant parts of the Galaxy.