The Constellation Cygnus
The Constellation Cygnus, also known as the Swan or Northern Cross, is one of the most fascinating and recognisable constellations in the night sky.
Cygnus’ northerly location makes it very accessible for observers in the northern hemisphere and its rich star fields and numerous deep sky objects have captivated astronomers for centuries.
In this post, we will explore how to find Cygnus it in the night sky and when is the best time of the year to view it. We will look into some of the key facts about this constellation, including its brightest and most interesting stars as well as explore the many nebulae and deep sky objects it contains.
Cygnus is a very rich and rewarding area of the night sky for both visual and astrophotographers alike, so whether you’re a seasoned astronomer or a curious beginner Cygnus has something to offer you.
Cygnus Constellation History
Cygnus is Latin for Swan. The constellation depicts a swan in flight with its wings opened and neck outstretched in front. It is one of the few constellations that has some resemblance to the thing it is trying to depict.
Cygnus is depicted as a swan in flight.
The Constellation Cygnus has been known since ancient times, perhaps as far back as the ancient Egyptians,
It has been depicted as a Swan since the time of the ancient Greeks and there are several stories and characters from Greek Mythology that have been associated with the constellation.
Cygnus was later listed as one of the 48 constellations contained within Ptolemy’s Almagest, written in about 150 AD, the Almagest contains some of the most comprehensive historical records about astronomy that we know of.
The constellation was officially recognised by the International Astronomical Union (IAU) in 1922, and it is now one of the 88 officially recognised constellations in the night sky.
If you want to read more about the story behind the constellation Cygnus you can find out more in my related post about the history and mythology of this fascinating constellation here.
How to find the Cygnus Constellation?
The best way to find where Cygnus is located in the night sky is first to familiarise yourself with the Summer Triangle asterism. The Summer Triangle is made up of the three bright stars Deneb in Cygnus, Altair in Aquila and Vega in Lyra.
It is referred to as the summer triangle as the centre of the triangle is located towards the zenith (directly overhead) during the summer months in the northern hemisphere. Due to the long twilight conditions at high northern latitudes during the summer months, the three bright stars of the Summer Triangle asterism are often the first to appear as it gets dark making it easy to identify.
The Summer Triangle asterism is made up of three stars: Deneb (in Cygnus), Vega (in Lyra) and Altair (in Aquila). Deneb (circled) is the most easterly star of the triangle
The Summer Triangle is an elongated isosceles triangle, that is, it has two long sides and one short side. It is a large triangle and covers a large area of the night sky. Deneb in Cygnus is located at the eastern corner of the triangle, shown in the chart above.
The star Deneb is a 1st magnitude star and is the brightest star in the constellation Cygnus, it marks the tail of the swan and it is from here that you can trace out the rest of the constellation Cygnus.
The Constellation Cygnus with names of the stars that make up the constellation’s outline (the Summer Triangle outline is included for reference).
Cygnus is also known as the Northern Cross due to its easily recognisable crucifix shape. From Deneb, the next star is the 2nd magnitude star Sadr which is located at the centre of the cross. Two further 3rd magnitude stars follow this line, Eta Cygni and Alberio. These comprise the ‘Neck’ and ‘Head’ of the Swan respectively.
Back from Sadr, the two other branches of the cross can be found. Moving southeast from Sadr are the 2nd magnitude star Gienah then the 3rd magnitude star Zeta Cygni. In the opposite northwesterly direction from Sadr, there is Fawaris and then three fainter stars Zeta, Iota and Kappa Cygni. These stars collectively make up the wings of the Swan in flight.
When is Cygnus visible?
August and September is the best time of the year to view Cygnus as the constellation will be high in the sky at a reasonable time of the night.
Cygnus will begin to appear in the spring months rising from the northeast at around midnight. During the spring months, Cygnus will continue to climb into the early morning sky until it is drowned out by the morning twilight.
Moving into the Summer months Cygnus will rise earlier and earlier. In July Cygnus will rise in the northeast at about 7 pm, however, due to the long twilight evenings, particularly at higher northern latitudes by the time it is dark enough to see Cygnus it will already be much higher in the sky.
The position of the Constellation Cygnus through the year is shown for a latitude of 51°N. Click the image for a larger view.
The months of August and September are often the best time of the year to view Cygnus. As Summer ends and autumn begins Cygnus will be high in the sky, close to the Zenith, at a reasonable time in the evening. The nights will also be drawing-in so you won’t need to wait long until it gets dark enough to be able to view it.
Cygnus will move further west into the winter months and appear lower in the sky. At more southerly northern latitudes Cygnus will disappear entirely below the horizon over the winter months. From the UK (around 51 degrees North) most of the constellation will dip below the Horizon during the winter months, but some of it will remain visible all year, albeit very low in the sky and difficult to view.
How many stars does Cygnus have?
The constellation Cygnus contains several bright and easily recognisable stars, including Deneb, which is the brightest star in the constellation and one of the most luminous stars known in the Milky Way galaxy.
Other notable stars in Cygnus include Albireo, which is one of the most striking double stars in the night sky, and Sadr which marks the centre of the cross and is surrounded by a large HII emission nebula region.
Below is a table showing how many stars of each magnitude are within the Cygnus constellation boundary. The 10 stars that make up the constellation’s distinctive swan outline are named the right-hand column.
| Magnitude range | Number of stars | Includes |
|---|---|---|
|
Brighter than 1st magnitude (<0.50) |
|
|
|
1st Magnitude (+0.50 to +1.49) |
1 |
Deneb |
|
2nd Magnitude (+1.50 to +2.49) |
2 |
Sadr, Gienah |
|
3rd Magnitude (+2.50 to +3.49) |
3 |
Fawaris, Albireo, Zeta Cygni |
|
4th Magnitude (+3.50 to +4.49) |
17 |
Iota Cygni, Kappa Cygni, Eta Cygni, Theta Cygni |
|
5th Magnitude (+4.50 to +5.49) |
51 |
|
|
6th Magnitude (+5.50 to +6.49) |
197 |
|
|
Total number of stars visible to the naked eye |
271 |
|
The constellation Cygnus is located within the plane of the Milky Way and contains many more stars that are fainter than magnitude 6.5 (the limit of human vision under very dark skies). Scanning over the constellation with a pair of binoculars will reveal rich star fields containing hundreds if not thousands of stars.
Deneb, Cygnus’ Brightest Star
Deneb, the brightest star in Cygnus, has an apparent magnitude of 1.25, which makes it one of the brightest stars in the night sky. This hot star is a blue-white super giant and is one of the most luminous stars in the night sky.
Deneb has a diameter 200 times larger than our Sun and combined with a high surface temperature of 8500K it is estimated that Deneb has a luminosity of up to 196,000 times that of the Sun.
Comparison in size of the star Deneb to our Sun, (sizes are approximate).
Due to Deneb’s high surface temperature, it has a blueish appearance which can be enhanced by viewing the star through binoculars or a small telescope.
Despite Deneb being located over 2600 light years from the Earth (the exact distance is still not known exactly) it is still the 19th brightest star in the night sky. Deneb’s absolute magnitude (its brightness when viewed from 10 parsecs away) is a staggering -8.40, at this distance, it would be brighter than the planet Venus and would easily cast clear shadows on a dark night.
Sadr
Sadr, also known as Gamma Cygni, is one of the brightest stars in the constellation Cygnus and is located about 1800 light years from Earth. With an apparent magnitude of 2.23 Sadr is easily visible to the naked eye and marks the centre of Northern Cross, close to Deneb.
Due to its surface temperature, which is approximately 5800K, Sadr has a white-yellow appearance. It has a large diameter of around 150 times that of the Sun, and its high surface temperature gives it a luminosity of 33,000 times that of the Sun.
Sadr is surrounded by a vast region of ionised hydrogen gas, this prominent HII emission nebula is one of the night sky’s largest and most beautiful. It can be seen visually through a telescope as a faint glow, but the best way to reveal its size and beauty is to photograph it.
Sadr is located just below the centre in this image and is surrounded by a large HII nebula region of ionised hydrogen. By Mike Soulby © stellardiscovery.com
The Sadr Region is a popular target for astrophotographers due to its size, brightness and relative ease to find.
Above is an image I took of the Sadr Region using a simple astro-modified DSLR camera on a star tracking mount. The image is in monochrome as it was shot through a hydrogen alpha narrowband filter clipped into my DSLR. This filter helps to isolate the specific emission wavelength of the ionised hydrogen improving the signal-to-noise. Sadr is the star located just below the centre in this image.
Albireo
Albireo is one of the most striking double stars in the night sky, located at the head of the swan with an apparent magnitude of 3.21 it is easily visible to the naked eye.
When viewed with the unaided eye Albireo appears as just a single yellow star, however, when viewed through a small telescope it is resolved into two stars of contrasting colour. The brighter of the pair Beta Cygni A (magnitude of 3.2), is amber-coloured, and its fainter companion star Beta Cygni B (magnitude 5.1) is blue.
Albireo and its contrasting companion star in Cygnus by Davide Simonetti (CC BY-NC 2.0)
The two stars are separated by 35 seconds of arc so can be easily separated in a small telescope. It is not certain if the two stars are gravitationally bound or if the pair is a chance line of sight double.
Once split in a telescope the colour contrast between the two is immediately apparent, the warm golden colour of the brighter star against the cool blue of the fainter companion makes this one of the most satisfying double stars to observe.
Cygnus Constellation Deep Sky Objects
Cygnus contains numerous beautiful nebulae and deep sky objects; it is one of the main reasons why the constellation is loved by astrophotographers. Not only are the nebula incredibly beautiful but they are also large and easy to find, making Cygnus a great starting place for any avid astrophotographers out there.
The positions of the major deep-sky objects in the constellation Cygnus are shown in the chart above.
Below are some highlights of the deep sky objects in Cygnus, including details about these nebulae and where they are located. I have also included some images that I have captured of these objects using relatively modest kit, consisting of a star tracker and a DSLR camera.
North America Nebula (NGC 7000)
The North America Nebula, or NGC7000 is a large nebula in the constellation Cygnus. Its distinctive shape resembles the North American continent and is how it gets its name.
The North America Nebula is one of the brightest nebulae in the night size making it an excellent target for astronomers. It has an apparent magnitude of +4.0 so it is technically visible to the naked eye, however, due to the nebula’s diffuse nature it requires very dark moonless skies to see even a hint with the naked eye. Even telescopes will only show this as a faint foggy patch.
As with almost all nebulae in the night sky, the best way to view the North America Nebula is to take a long-exposure photograph of it. Below is an image I took using a DSLR fitted with the fantastic Samyang 135mm f/2 lens. This 50-minute exposure (25x2min sub-exposures) was taken from a Bortle 3 sky.
The North America Nebula (NGC 7000) region in Cygnus by Mike Soulby © stellardiscovery.com
The North America Nebula (NGC7000) is on the left of the image.
The North America Nebula is located close to the bright star Deneb making it an easy target to find for beginners. This is also a large nebula and spans an area of approximately 2.0° x 1.6° which is equivalent to about four times the diameter of the full Moon.
The North America Nebula is an example of an HII region, which is an emission nebula where the hydrogen gas is ionised by the intense radiation emitted by very hot nearby stars.
The Pelican Nebula (IC 5070 / IC 5067)
The Pelican Nebula (IC 5070 / IC 5067) is located immediately next to the North America Nebula in Cygnus and the two nebulae are often featured together in images. The Pelican Nebula is part of the same nebula complex as the North America Nebula but they are separated by a dark dust band that lies in front, blocking the nebula’s light.
The Pelican nebula gets its name from its resemblance to a pelican, with its long bill and large throat pouch.
Below is an image I captured of the Pelican Nebula (right) and the North America Nebula (left). This image was taken using the William Optics Zenithstar 73 II APO widefield telescope and an astro-modified Canon EOS 200D DSLR camera.
The Pelican Nebula (IC 5070 / IC 5067) (right) and the Cygnus Wall within the North America Nebula (left) by Mike Soulby © stellardiscovery.com
Butterfly Nebula / Sadr Region
The Butterfly Nebula and surrounding region around the star Sadr is a very large HII gas cloud complex that covers a large area of the constellation Cygnus.
It is also possibly one of the easiest deep-sky objects to locate and photograph. By simply centring the star Sadr in your camera’s frame you will capture large parts of this nebula, particularly if you are using a DSRL and lens or a small widefield telescope setup (up to about 300mm focal length).
The Butterfly Nebula region is located just below the star Sadr in the image below. It contains two large bright areas that look like the wings of a butterfly.
The Sadr HII region and the Butterfly Nebula, Sadr is located just below the centre in this image. The Crescent Nebula is also visible in the top right. By Mike Soulby © stellardiscovery.com
To help reveal the detail and structure of the hydrogen gas within the nebula I used a 12nm hydrogen-alpha (Ha) clip-in filter with my astro-modified DSLR camera. The filter only lets through the specific hydrogen-alpha emission wavelength of 656nm.
Narrowband Ha exposures like this one are often used to enhance full colour (RGB) images, improving the luminosity, detail and contrast of faint nebulae.
Veil Nebula (Cygnus Loop)
The Veil Nebula is a fascinating supernova remnant in the constellation Cygnus. This nebula is the remains of a supernova explosion that occurred only 15,000 – 20,000 years ago; yesterday by cosmic standards.
The entire nebula is referred to as the Cygnus loop as the bubble of expanding gas creates a kind of loop shape. This loop is made up of several main nebula components. The Eastern Veil Nebula (on the left of the image below), Pickering’s Triangle (top/centre right part of the loop) is a faint triangle or wedge-shaped feature and the Western Veil Nebula (right) is referred to as the Witch’s Broom due to its long thin flowing filaments.
The Veil Nebula or Cygnus Loops is a supernova remnant in the constellation Cygnus. By Mike Soulby © stellardiscovery.com
The red colour in this image is ionised hydrogen (H-alpha) and the teal colour is ionised oxygen (OIII). I used the Optolong L’eNhance triband filter to capture this image, it helps to isolate the key wavelengths emitted by the nebula.
More importantly, the filter helps to reduce the effects of light pollution dramatically! Allowing images like this one to be captured from a light-polluted backyard.
The Crescent Nebula (NGC 6888)
The Crescent Nebula (NGC 6888) is a small but distinctive emission nebula in the constellation Cygnus. The nebula is irradiated by a close-by Wolf-Rayet star, these massive stars have burnt through their hydrogen fuel and are now fusing Helium. These stars are some of the hottest known with surface temperatures in excess of 200,000°K.
The outer layers of the Wolf-Rayet star that radiates the Crescent Nebula are being thrown out into space creating ferocious stellar winds that buffet and collide with other more slowly moving gas that was previously ejected from the star. The collision of these fast-moving gasses excites the gas clouds
The Crescent Nebula (NGC 6888) by Darko7411 (CC BY-SA 4.0 via Wikimedia Commons)
Visually the nebula is small, faint and diffuse (magnitude 7.4). A telescope with a large aperture would be needed to reveal this nebula visually and will likely require an additional filter to bring out any detail.
Photographically the nebula can be captured with modest equipment or a widefield setup, but it will appear small. A telescope with a longer focal length will reveal a close-up and more detailed image.
Other Deep Sky Objects in Cygnus
Due to the position of Cygnus in the plane of the Milky Way it has a high density of stars which makes scanning across the constellation with a pair of binoculars very rewarding, particularly if you can do this during the new Moon phase and well away from light-polluted skies.
There are also several open star clusters in Cygnus. If you are observing with a pair of binoculars or a small telescope at low magnification these are definitely worth seeking out.
Open Cluster M29
Located close to the star Sadr this small open cluster has an apparent magnitude of +7.1 so it is not visible to the naked eye, but worth seeking out with binoculars under dark skies.
The cluster is small and can seem insignificant against the rich star fields in Cygnus. It has an angular size of just 7 arc minutes and contains more than 20 stars, its brightest stars create a small quadrilateral shape and is sometimes referred to as the Cooling Tower.
Open Cluster M39
M39 is located a little way out from the main constellation, about 9 degrees away from the bright star Deneb. It has an apparent magnitude of +4.6 so can be seen with the naked eye as a small fuzzy patch north of Deneb under dark skies.
M39 contains about 30 to 40 stars spread across about 30 arc minutes of the sky (about the same size as the full Moon). A pair of binoculars or a small telescope at a low magnification will begin to resolve the individual stars in the cluster.
Final Thoughts
This has turned out to be quite a long post, but that just goes to show what a fascinating constellation Cygnus really is; with the many interesting stars and deep-sky objects that it contains.
Its distinctive shape and dense star fields make this a great constellation to seek out and scan across with binoculars or a small low-powered telescope.
For astrophotographers, Cygnus has a special attraction due to the many large, bright and beautiful nebulae it has to offer. There is enough to photograph in just this one constellation to keep you busy for years!
All star charts in this post were generated by Starry Night Enthusiast 8 © Copyright Simulation Curriculum Corp. All rights reserved. www.starrynight.com
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