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Cygnus

by | Oct 22, 2021 | 0 comments

Cygnus, the Swan, is one of the best-known constellations of late summer and fall. This constellation lies high overhead after dark at mid-northern latitudes during October, although it has already been well-placed for observing for the last several months. Along with forming the shape of a swan, most of the stars of Cygnus make up an asterism (grouping of stars that is not a constellation) called the Northern Cross. Deneb, the brightest star of Cygnus, marks the tail of the Swan and the head of the Northern Cross. This star is also the northeastern star in another asterism, the Summer Triangle.

Thanks to its location along the Milky Way, Cygnus is loaded with star clusters and nebulas. It also contains a couple of outstanding double stars.

Albireo, the star marking the head of Cygnus, is one of the most famous and beautiful double stars in the sky. With its blue and gold component stars, Albireo is the benchmark against which other color-contrast double stars are measured. This double is wide enough to split in any telescope, and a good 10× binocular should even be able to split it. A telescope at low magnification will probably give the most pleasing view.

A very different pair of stars, 61 Cygni, lies on the other side of Cygnus. This double is one of the nearest stars to Earth, at a distance of about 11 light-years. In fact, it is so close to Earth that careful telescopic observation over a number of years will allow you to see the pair moving in relation to the more distant stars around it. Both stars appear orange, with the fainter one appearing slightly deeper orange. Low magnification will nicely split the pair. To find 61 Cygni, first locate Tau Cygni, which completes a lopsided rectangle with the stars Deneb, Sadr, and Gienah. Our target double lies about 1.5° northwest of Tau Cyg.

The Veil Nebula (NGC 6960, 6992, 6995), Cygnus’ most impressive nebula, spans several degrees and lies 2–4° south and southeast of Gienah. The Veil is a supernova remnant that is divided into several sections of wispy filaments of nebulosity. The eastern section of the Veil is the brighter section. The western half is slightly dimmer, but it passes directly behind a (comparatively) bright star, 52 Cygni. Incidentally, this star is a beautiful double. You may need moderate to high magnification to split this double since it is somewhat tight (6”), and the secondary component star is 4.5 magnitudes fainter than the primary.

Since the Veil Nebula is such a large object, it generally looks best at low magnifications. The eastern and western halves of the Veil are much too far apart to fit in the same telescopic field of view, so plan to look at them individually. Also look for fainter nebulosity between the two brighter sections. The Veil can be quite difficult to see without a filter under mildly light-polluted skies, but an OIII or UHC filter enhances the nebula’s contrast considerably. Of course, a really dark sky also helps a lot.

North American Nebula
North American Nebula. Photo © Shaphan Shank

The North America Nebula (NGC 7000) is nearly as large as the Veil, although it gets a bit less attention from stargazers. This nebula, which is actually shaped much like the continent, lies about 3° east of Deneb. The North America Nebula is more of a large cloud than a finely structured wisp like the Veil. However, it is still a fascinating sight at low magnifications.

Under dark skies, the North America Nebula is visible to the unaided eye as a slight brightening of the Milky Way. A binocular may begin to show the nebula’s shape, but the best views come with a telescope using the lowest magnification possible. The North America Nebula is too large to completely fit in the field of view of most telescopes, so look for the contrast between the edge of the nebula and the darker sky around it. The nebula’s surface brightness is fairly low, so its edges will be the easiest parts to see. The nebulosity around the “Gulf of Mexico” is especially easy to see.

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