Before this post, most of the constellations I have explored have been those visible in the Northern Hemisphere, but I wanted to explore some which are located in the Southern hemisphere as I don’t know half as much about them as I do with those constellations in the Northern hemisphere. Sagittarius is a constellation that is located right on the richest area of the milky way and contains several star clusters, nebulae and the supper massive black hole that is thought to be the very centre of our galaxy. I think that makes it a very special constellation that is worth exploring a bit.
Sagittarius is typically known as the archer, as the Ancient Greeks imagined it to be a centaur with a bow and arrow although other ancient civilizations saw it as a horse and rider. the constellation borders several other ancient constellations such as Scorpius the scorpion and Aquila the eagle as well as a few of the more modern constellations like Microscopium.
As I mentioned earlier, Sagittarius is rich in deep sky objects. the Trifid nebula is one of the finest objects to observe in Sagittarius. It gets its name from the dark ribbons of dust that split the bright areas of gas into three sections. the Trifid nebula which is also known as M20, is rare by the fact that it is made up of an emission nebula which gives the nebula a pink glow; a reflection nebula that adds shades of blue as well as a star cluster, making it a beautiful site through a small telescope.
Sagittarius also holds a globular star cluster known as M54 which on the surface seemed to be like any other globular star cluster. But on closer inspection it was found that M54 didn’t originate from our galaxy at all. it came from a dwarf galaxy that was in the process of colliding with the milky way, called Sagittarius Dwarf Elliptical or SagDEG meaning that M54 was a globular cluster from another galaxy that was in the process of being captured by our galaxy, the Milky Way.
Another nebula located in Sagittarius is M8 or the Lagoon nebula is home to a star forming region that is visible to the naked eye at magnitude 6, of which there are only 2 in the northern hemisphere. However it is best to use binoculars or a small telescope if you want to see the detail in all its glory. binoculars will show a bright nucleus in the glowing cloud of gas and dust which is spread across the equivalent area of 3 full moons. A small telescope will reveal this plus more detail of the nebula including streams of dust that give the nebula its name. there is also a star cluster named NGC 6530 that is located in the eastern half of the nebula and is thought to be full of young stars which have emerged in the previous 2 million years.
Sagittarius is the constellation that is home to an object that has the potential to be a super massive black hole which is responsible for holding our entire galaxy together under its eminence gravitational strength. This area that has been frequently investigated by the Hubble space telescope, is known as Sagittarius A* and these observations have found several star clusters containing giant stars, that have been orbiting this object that contains 4 million solar masses of material in an area that is smaller than the orbit of the planet Uranus. this object is not visible and so has provided evidence for a supper massive black hole that is at the heart of the Milky Way.
Sagittarius is a constellation that is well worth exploring if you can, and if i am ever under clear skies in the southern hemisphere I will grasp the opportunity to look up. it is not only full of beautiful objects for us to look at but also contains one of the most powerful sources of gravity ever known, and I think that really adds to its mystery and wonder.
- information on Sagittarius and all the objects mentioned in the above article is sourced from ‘Constellations A field guide to the night sky’ by Giles Sparrow (ISBN: 978-1-78087-815-7)