Solar System


One of the heroic constellations, Hercules was one of the classical Greek heroes that many people recognise due to epic motion pictures.

Hercules was the son of Zeus and Alkmene although Zeus was actually married to Hera at the time. Because the unfaithfulness of Zeus enraged Hera, she punished Hercules with one gigantic task. This task is actually what made Hercules famous, the undertaking of the twelve labours.

The most well known of these was the quest to destroy Hydra the nine headed serpent. During the battle with Hydra, Hercules also ended up killing Cancer the crab although this wasn't one of the twelve labours. Other labours included strangling the lion of Nemea, killing the Stymphalion Birds and to tame the maneating horses of King Diomedes. What most people don't know is that the actual Greek name of Hercules is Heracles, the name that is popularly used is Roman in origin.

The constellation of Hercules is quite bright with the main part being made up of four stars. These four stars form a well known summer asterism, the Keystone. The four stars are Pi, Eta, Epsilon and Zeta Herculis. Unknown to some individuals is the fact that Hercules is actually the fifth largest constellation in the sky. The brightest star is called Ras Algethi and is interestingly both a variable and double star. It has an unmistakably deep red colour and has a blue companion that is unrelated to it and requires a small telescope to be seen.

One of the greatest globular clusters resides in Hercules, M13 is undoubtedly the most spectacular globular in the northern sky and a brilliant attraction for newcomers to astronomy. It even shares the noble heroic qualities of Hercules, it can convince people to get interested in astronomy! A superb showcase object to observe at summer star parties, not once has it failed to delight! If you don't believe this, convince yourself by taking a glance at the dazzling image below!

Other deep sky objects that are brilliant are numerous planetary nebulae and densely populated galaxy clusters.

Great Hercules Cluster    
An icon of astronomy, the Great Hercules Cluster is undoubtedly the greatest globular in the northern celestial hemisphere. Even though it is 12 billion years old, it will continue to twinkle in the eyes of both the young and the old for many centuries to come.    
Image copyright R. Croman
Great Hercules Cluster (M13):

A deep sky object with the word 'great' in its name has huge expectations to live up to, fortunately this impressive globular cluster exceeds those expectations with considerable aplomb. It can be seen in the sky as a faint magnitude 5.6 point of light below Eta Herculis, the star that consitutes the upper right corner of the Keystone asterism. It wasn't until 1714 that its true nature was revealed by Edmond Halley.

The stellar population is vastly abundant with an estimated number of 700 000 members. The distance of M13 has been calculated to be 25 000 light years. Observers with large telescopes might be able to find a galaxy near M13, NGC 6207.


Woefully ignored in favour of its more famous cousin, M92 is a truly fantastic globular cluster but its lack of attention is quite unfair as it is spectacular in its own right. It is quite similar to M13, the distance is 26 000 light years and the brightness is only one magnitude fainter. It was discovered in 1777 by Johann Bode.

Turtle Nebula (NGC 6210):
This planetary nebula actually does resemble a turtle when seen through a large telescope! It is very bright at magnitude 9 and looks like a blue star in small scopes. Since the size is small, you might think that it is very distant, a large gap of 5000 light years separates it from us and the diameter is less than one light year!
Hercules Galaxy Cluster (Abell 2151):

When you look at this galaxy cluster, the light that reaches your eyepiece is 500 million years old! This is another celestial object that demonstrates the infinitely incomprehensible vastness of the universe and how humanity is virtually nonexistent in the enormity of the cosmos.

Despite the immense distance, the galaxies in the cluster look fairly large in size suggesting that they are behemoths. The number of galaxies in the cluster is quite considerable at a number of 100 and the cluster has a diameter of 6 million light years! The brightest galaxies are magnitude 13 so very dark skies are a necessity.

Abell 2151 is a spiral rich galaxy cluster and this suggests that it is quite young.
More evolved galaxy clusters are populated with mostly elliptical galaxies. As time goes on, the members of a galaxy cluster interact with each other and gas and material is stripped from some galaxies and added to others and this process is responsible for reducing bright blue spirals into golden featureless ellipticals.

Abell 2151 is a treasure for fans of peculiar galaxies, numerous interacting pairs can be seen as well as mergers. One example is the largest galaxy in the cluster,
IC 1182. This galaxy looks like an elliptical with what looks like a huge jet bursting out from the centre as well as remnants of a spiral arm attached to the left side of it.

What is evident in the abundance of interacting and merging galaxies is that the members of the cluster are closely packed together and the gravity of each member is wreaking havoc on adjacent galaxies. It is a true joy to explore this galaxy cluster with a very large telescope and witnessing the bizarre and chaotic forms of the deformed galaxies is a memorable sight that will fill you with awe of the majestical nature of the universe.

The Hercules Galaxy Cluster is part of a larger supercluster that is comprised of 12 Abell galaxy clusters. The Hercules Supercluster is a component of one of the largest structures ever found, the Great Wall.

The Great Wall is a huge sheet like structure that spans 500 million light years and it was discovered in the 1980's by Margaret Geller and John Huchra. The Great Wall consists of many rich galaxy clusters that include Abell 1367 in Leo, Abell 1656 in Coma Berenices and Abell 2147, Abell 2151, Abell 2197 and Abell 2199 in Hercules.

Abell 39:
An unbelievably faint planetary nebula, this is only visible to owners of very large telescopes. The magnitude 14 shell is 5 light years across at a relatively nearby distance of 7000 light years. Through and around the shell are dozens of miniscule background galaxies that can only be seen in photographs.
Abell 2199:

Located towards the north of the Hercules Supercluster, this galaxy cluster is also the closest in the supercluster at a distance of 400 million light years. Unlike Abell 2151, a centrally dominant elliptical galaxy is present and is the largest member of the group. This galaxy is NGC 6166 and shines at a faint magnitude of 13.

Altogether there are 90 galaxies in Abell 2199 and the brightest can be seen in medium sized scopes. Below NGC 6166 is a chain of face on and edge on spiral galaxies, the distribution of the other members is rather dispersed and the space surrounding the main region is sprinkled with many other spiral galaxies.

Another factor that isn't shared with Abell 2151 is the 'normal' state of the galaxies, it is likely that interactions between the member galaxies happened many millions of years ago and resulted in the giant elliptical galaxy NGC 6166. Another possibility is the slightly wider dispersal of the cluster prevents galaxies from gravitationally interacting with each other.


One of the most popular galaxy clusters is Abell 2151 and one unique aspect is the lack of a centrally dominant galaxy as well as the distribution being mainly spiral. Many of the galaxies are tearing each other apart and many are in the process of merging. Since we see it as it looked 500 million years ago, it is plausible that right now some of the interacting pairs have merged into large single galaxies although we will never be able to see the completion of the mergers. IC 1182 is the largest galaxy and can be seen towards the bottom of the image, it is the one with the giant jet like structure. This feature is actually a tidal tail and if you look closely, knotted regions can be seen at the end of it. These might either be HII regions or tidal dwarf galaxies forming in the aftermath of the collision.

The Hercules Galaxy Cluster contains four galaxies that are catalogued in the Arp Atlas. The interacting pair that is below centre is NGC 6050 and IC 1179 and both have the alternative designation of Arp 272.
The spindle shaped edge on galaxy that is to the left of NGC 6050 is NGC 6045, also known as Arp 71. The exotic looking interacting elliptical and spiral in the top left corner is Arp 122. The spiral galaxy is NGC 6040A and the elliptical galaxy is NGC 6040B. The bizarre tangle of galaxies that is the interacting pair near the top right corner with streamers stretching outwards is Arp 172. In the pair, the one on the left is IC 1178 and the other one is IC 1181.

Besides the large galaxies visible, hundreds of small background galaxies can also be seen, particularly noteworthy is the distant chain of galaxies above Arp 122. Most of the background galaxies aren't members of the cluster and are even more distant than the 500 million light years distance of Abell 2151! Even more unbelievable is that this galaxy cluster shares a line of sight with 12 quasars that are estimated to be 11 billion light years away! If you are unsure about which galaxy is which, then mouseover each one.

Image copyright T. Hallas
NGC 6050 and IC 1179 (Arp 272) NGC 6045 (Arp 71) IC 1182 NGC 6040A and NGC 6040B (Arp 122) NGC 6041A and NGC 6041B NGC 6042 IC 1178 and IC 1181 (Arp 172) IC 1185 NGC 6043 IC 1170 NGC 6044 NGC 6047 NGC 6054 IC 1184 UGC 10190