Solar System

(The Eagle)

Aquila is a fantastic bright constellation visible in summer skies. It contains a wide variety of deep sky objects and also the Milky Way runs through it. It also contains one of the 20 brightest stars, Altair. Altair is one of the stars that makes up the summer asterism known as the Summer Triangle alongside with Deneb in Cygnus and Vega in Lyra. This makes the constellation easy to find near the horizon in the north and high in the sky in the south.

Aquila is akin to being an interstellar graveyard, there are at least a dozen planetary nebulae within its boundaries.

NGC 6709:
  A very old open star cluster at about 300 million years old, NGC 6709 is a fairly easily visible cluster that contains about 50 stars. It lies at a distance of 550 light years and can be found southwards of the star Zeta Aquilae.
NGC 6781   NGC 6781:
  A quite bright planetary nebula that is similar in colour to the Helix Nebula. The gases inside the nebula are expanding constantly but there will be no noticeable difference in a lifetime. The central star is a blue dwarf, which can be seen in the image to the left.
Barnard's E (B142-3) :
This is a dark nebula that blocks out the light of the Milky Way behind it. It can be seen with the naked eye in dark places such as Namibia. B142 is a C shaped nebula and B143 is a stripe underneath B142 and both form an E. It was discovered by the astronomer Edward Emerson Barnard.
NGC 6781 is reminiscent of the Helix Nebula in Aquarius. Subtle hints of a halo can be seen towards the southern part. Click on the image for a larger version.
Image copyright Capella Observatory

Barnard during the early 20th century took very widefield photographs of the Milky Way and found a myriad of dark dust clouds that looked like ink spilt on the sequinned golden blanket that was the Milky Way. He catalogued them and his initial publication was in 1919 and consisted of 182 objects. Unfortunately he died in 1923 and posthumously, his catalogue was published as the Photographic Atlas of Selected Regions of the Milky Way. The final version contained 370 dark nebulae and is popular with amateur astronomers. The most famous of the Barnard nebulae is B33, more commonly known as the Horsehead Nebula. Another one that is popular is B72, the Snake Nebula in Ophiuchus.

Other achievements of Edward Emerson Barnard include the first discovery of a comet via photography as well as the little known yet brilliant fact that he discovered the fifth moon of Jupiter, which earned him the Lalande Gold Medal awarded to him by the French Academy of Sciences. He also challenged the perceptions surrounding the nature of dark nebulae, the general consensus of his time was that they were literal holes in the sky. He was the first to consider that they might be clouds of dust between us and the Milky Way. He was indeed a remarkable individual who was both resilient and persistent in his study of the universe.

NGC 6772:
An endearingly odd planetary nebula, NGC 6772 stands out from the crowd in Aquila by being oval shaped as opposed to spherical. As with many others, it has a thin outer part that is rosy pink and an inner part that is blue. This could be considered as the challenge object of Aquila, it is magnitude 14. If that's too easy for you to see through a telescope, try glimpsing the central blue star that is magnitude 18!
NGC 6804:
A round greenish planetary nebula with a torus shaped structure. It also has an outer halo that is visible with special filters. Other planetaries that have outer haloes are the Ring Nebula in Lyra and the Dumbbell Nebula in Vulpecula. NGC 6804 is 4200 light years away and would appear vastly larger if placed at one tenth of its distance as it isn't too small.
NGC 6814:

Since most of Aquila has the gushing ocean of the Milky Way running through it, it would be unexpected to find a fairly bright galaxy within its confines. NGC 6814 is a highly enchanting gem of a spiral galaxy that despite being the brightest, is still only magnitude 13. The cause for the lack of luminosity is interweaving strands of dust within the Milky Way.

Numerous spiral arms sprout from a very active nucleus that has been found to have a regular period of x-ray variability. Since it is a very active galaxy, there are multiple HII regions adorning the spiral arms.


Another planetary nebula, but with a difference, this one is red and is also bipolar. This means that instead of being spherical, it has two parts that are opposite each other. It slightly resembles a pair of lips and this unreal structure is caused by a binary star near the centre. Sh2-71 was discovered in 1946 by Rudolph Minkowski.

The Sh stands for Sharpless and is a catalogue of HII regions that were catalogued in the 1950's by an astronomer called Stewart Sharpless. The number 2 refers to "HII", this is an abbreviation used to describe objects that contain ionized hydrogen. Objects that contain doubly ionized gas have three "I's". If you're wondering what "HI" represents, it is neutral hydrogen.

Altogether there are 313 nebulae in this catalogue. Famous Sharpless nebulae include the Cave Nebula (Sh2-155) in Cepheus and Barnard's Loop (Sh2-276) in Orion.

Abell 70:

The universe is an unimaginably vast place, incomprehendible distances can separate objects. On the other hand, they can also be brought closer together by sharing a line of sight with two objects of wildly differing distances being daubed on the canvas of the night sky.

This intriguingly faint planetary nebula is one example of this. It lies at a distance of thousands of light years and is a thin shell of ionized gas. The northern part is thinner than the rest, as if it has a crown, the bright milky glow of a small galaxy can be seen twinkling from a huge distance of tens of millions of light years! This poignant juxtaposition of the near and the far is a lesson in how obstacles can be crossed to create a memorable vista, saddeningly this cannot last forever. Planetary nebulae usually only last for ten thousand years and the shell will fade away to nothingness, nothing remaining to suggest that they once occupied a little piece of the universe.

Abell 53:

A faint reddish orb of a planetary, the small apparent size makes large apertures a necessity to see its feeble disk. The edges are brighter because the gas is more concentrated in those areas, this is known as limb brightening.

The Abell catalogue of planetary nebulae, not to be confused with the Abell galaxy cluster catalogue, was published in 1966. They were found by George Abell who also catalogued thousands of galaxy clusters by using the exact same methodology, closely scrutinizing photgraphic plates taken by the Palomar Observatory in the 1950's. Several of them are actually not planetary nebulae. For example Abell 85 in Cassiopeia is in fact a supernova remnant. Other astronomers have also made mistakes while compiling their catalogues. One of the "nebulae" in the Sharpless catalogue is actually a galaxy! In 1976, it was found that Sh2-191 in Cassiopeia was actually a galaxy, now known as Maffei 1.

Even though there are only 86 in total, they are regarded as difficult to observe so they are usually sought out by advanced observers with large telescopes. If you don't have one already, an OIII filter is an essential requirement in hunting them down.
The most well known one is the also the only Abell planetary with a popular name, the Medusa Nebula (Abell 21) in Gemini. Others familiar to some include Abell 39 in Hercules and Abell 33 in Hydra.