TSS Monthly DSO Challenge – August 2021
Posted: Sun Aug 01, 2021 7:56 pm
Welcome back and here we are in another new month, with another new list of objects for you to pursue. Last month we relied heavily on the Messier list, but this time we only have one such object. For the northerners among us, we shall visit the constellation of Cygnus the swan and Cepheus the king. For our southern friends, we shall swing by Pavo the celestial peacock and Telescopium the telescope. So let’s dig into the offerings for this month and do some observing, sketching and imaging – your choice! 
Northern Celestial Hemisphere
Messier 29 / NGC 6913 (Cygnus, open cluster, mag=6.6, size=10.0’, class= III3p):
MonsieurMessier discovered this object 257 years ago, on 29 July 1764. While not the richest open cluster in his list, it is nonetheless a pretty little grouping that is roughly trapezoidal in shape. Well detached in a rather rich field, it is located less than 2° SSE of mag 2.2 Gamma Cygni (Sadr). It carries the curious nickname of the “Cooling Tower” which I guess is up to one’s imagination.
NGC 6939 (Cepheus, open cluster, mag=7.8, size=10.0’, class= I1m):
In the western extension of Cepheus, that juts westward between Draco and Cygnus one can find this nice open cluster. Discovered by William Herschel in 1798, he described it as "a beautiful compressed cluster of small stars.” It is indeed a pretty and well compressed cluster that responds well to increases inaperture and magnification, revealing more and more resolution with the persistent presence of unresolved members forming a gauzy backdrop.
NGC 6946 (Cygnus, barred spiral galaxy, mag=8.8, size=11.5’x9.8’, SBr=13.8):
This showpiece face-on barred spiral has the unique nickname of the “Fireworks Galaxy” because of the 10 (so far) supernovae that have been observed within it during the 20th and 21st centuries. Discovered by William Herschel during the same sweep in 1798 asNGC 6939, the two objects lie only about 29.5’ apart, with the cluster positioned northwest of the galaxy. They form an interesting contrast in a lower magnification wide field view. Don’t let the brighter visual magnitude of NGC 6946 fool you, as it can be challenging from more light polluted areas due to its large angular size and face-on orientation. This lowers its surface brightness to the point that it is frequently seen as only a very dim hazy patch that struggles to overcome the sky glow imparted by artificial lighting. Where it really shines, visually, is in darker locations where its lower surface brightness is not as much of an issue. Under those conditions it can be an obvious large oval glow that may reveal delicate and diaphanous spiral structure to the eye.
Southern Celestial Hemisphere
NGC 6584 (Telescopium, globular cluster, mag=7.9, size=6.6’, class=8:
The celestial telescope is one of 14 constellations still in use today that were created by Nicolas-Louis de Lacaille to honor key inventions, in this case the telescope. Though not a bright constellation (brightest star Alpha is mag 3.5), we nonetheless enter its realm in pursuit of this small globular cluster. Discovered by James Dunlop in 1826, he described it as “a pretty bright round nebula.” Located about 3.5° SSW of mag 4.1 Zeta Telescopii, it forms a triangle with two 7th mag stars to its north and northwest. In smaller apertures one might see some subtle core brightness, and even with largeraperture it yields only very modest resolution of member stars.
NGC 6752 (Pavo, globular cluster, mag=5.3, size=29.0’, class=6):
South of Telescopium one enters the realm of the celestial peacock. Though not a particularly bright constellation as a whole, its main star, Alpha Pavonis (Peacock), does shine brightly at magnitude 1.9. First up is this showpiece globular cluster. Another Dunlop discovery from 1826, it is a stunning visual and imaging target that may reveal significant resolution in its halo and across the core with moderately largeaperture (8 to 12 inches). When seen nicely elevated above the horizon it can be a naked eye object and easily swept up in small instruments. Images reveal a dizzying array of stellar points. Look for this stunning visual treat 1.5° east of mag 5.1 Omega Pavonis, and be prepared for a visual treat!
NGC 6744 (Pavo, barred spiral galaxy, mag=8.5, size=20.1’x12.9’, SBr=14.3):
We wrap up this month by staying in Pavo to hunt down this beautiful barred spiral galaxy. Once again, Dunlop gets the credit in 1826 for its discovery. As withNGC 6946 in Cygnus, don’t be fooled by its bright visual magnitude. Another face-on spiral with a larger angular size ensures its surface brightness is lower. Therefore in areas with noticeable light pollution, or when it is at lower elevations, its visual appearance becomes muted. In darker locations it may reveal very subtle hints of spiral structure in moderate apertures, but it is not boldly evident, even in larger apertures. Overall it is a delicate diaphanous oval glow that has a ghostly appearance to the eye.
Okay folks, there you go. I've given you just a few treats to add to your observing/imaging plans this month. I know they are not new to everyone, but it never hurts to revisit an old friend from time to time. Though our sky friends get older just like we do, they always seem to look the same and no worse for the wear of aging – unlike us! Good luck and please report any observations, sketches and/or images of the above objects here so that we can share in your successes.
Northern Celestial Hemisphere
Monsieur
In the western extension of Cepheus, that juts westward between Draco and Cygnus one can find this nice open cluster. Discovered by William Herschel in 1798, he described it as "a beautiful compressed cluster of small stars.” It is indeed a pretty and well compressed cluster that responds well to increases in
This showpiece face-on barred spiral has the unique nickname of the “Fireworks Galaxy” because of the 10 (so far) supernovae that have been observed within it during the 20th and 21st centuries. Discovered by William Herschel during the same sweep in 1798 as
Southern Celestial Hemisphere
The celestial telescope is one of 14 constellations still in use today that were created by Nicolas-Louis de Lacaille to honor key inventions, in this case the telescope. Though not a bright constellation (brightest star Alpha is mag 3.5), we nonetheless enter its realm in pursuit of this small globular cluster. Discovered by James Dunlop in 1826, he described it as “a pretty bright round nebula.” Located about 3.5° SSW of mag 4.1 Zeta Telescopii, it forms a triangle with two 7th mag stars to its north and northwest. In smaller apertures one might see some subtle core brightness, and even with larger
South of Telescopium one enters the realm of the celestial peacock. Though not a particularly bright constellation as a whole, its main star, Alpha Pavonis (Peacock), does shine brightly at magnitude 1.9. First up is this showpiece globular cluster. Another Dunlop discovery from 1826, it is a stunning visual and imaging target that may reveal significant resolution in its halo and across the core with moderately large
We wrap up this month by staying in Pavo to hunt down this beautiful barred spiral galaxy. Once again, Dunlop gets the credit in 1826 for its discovery. As with
Okay folks, there you go. I've given you just a few treats to add to your observing/imaging plans this month. I know they are not new to everyone, but it never hurts to revisit an old friend from time to time. Though our sky friends get older just like we do, they always seem to look the same and no worse for the wear of aging – unlike us!
Good luck and please report any observations, sketches and/or images of the above objects here so that we can share in your successes.