Constellation Profile - Sagittarius

The constellation of Sagittarius is well known as it one of the most popular in the zodiac.  The zodiac is a region in the sky approximately 8° North and South of the ecliptic.  This is the area of the sky the Sun, Moon and Planets transit.  If you were to look at the planets in the sky they would likely be within the borders of a zodiac constellation.

There are several myths associated with Sagittarius.  It is well known that this constellation represents the archer.  The Greeks represent Sagittarius as a centaur who is aiming his arrow toward the heart of Scorpius--the bright red star Antares.  In mythological tradition the scorpion killed Orion and is now seen chasing the great hunter out of the sky in the Spring.  Sagittarius keeps a watchful eye on Scorpius to ensure he does not sting Orion again.

The chief librarian at the Library of Alexandria, Eratosthenes, believed that Sagittarius represented a satyr and not a centaur.  The satyr Crotus is a mythological being known to be the son of Pan.  He is credited with inventing archery and was an excellent hunter.  He kept the company of the Muses and is also credited with inventing applause.  The Muses, in their great love for him, requested Zeus to put him in the sky.

Sagittarius (Artist Interpretation)

For observers in Calgary, most of Sagittarius can be found transiting the southern sky just above the horizon throughout the Summer around midnight.  If you are at a dark site you will notice the Milky Way and the Galactic Center find their home in this constellation.  Within the constellation, the radio signal known as Sagittarius A* is thought to be the location of the supermassive black hole around which our galaxy orbits.

Sagittarius was the most difficult constellation to map so far in my journey through the sky.  It's declination runs from about 12°S to 46°S.  At the latitude in Calgary (~51°N) we can only see to approximately 39°S depending on altitude and topography.  This rendered the southern regions of the constellation forever buried beneath the horizon.  The Summer is the best time to map Sagittarius as it reaches its greatest height above the horizon while the Sun is on the opposite side of the Earth.  This poses additional challenges from 51°N with constant astronomical twilight from the end of May to mid-July.  The Summer also offers a plethora of bugs that can completely destroy an entire night of observing.

I mapped Sagittarius over the course of 3 separate calendar days.  I started late on July 9, 2018 which carried me into the morning of July 10, 2018.  I went out during the evening of July 11, 2018 to a high altitude location with a clear view of the southern horizon.  On this night I was able to find Epsilon, Eta and Theta Sagittarii hovering just a few degrees above the horizon.  Alpha, Beta, Iota and Kappa Sagittarii are permanently below the horizon from Calgary and thus so indicated on the observation record below.

Sagittarius Observation Record

Sagittarius is the 15th largest constellation and it contains many Bayer stars.  It took a long time scaling my observations onto the Powerpoint slide above.

There are several interesting asterisms that can be seen above.  The most famous is the teapot.  The westernmost part of the constellation contains many bright stars in the pattern of a teapot.  Adding to the effect is a lemon wedge on a spoon to the upper left of the teapot.  The Milky Way flows right through the teapot making it look like an enormous amount of steam billowing out.  This is why a spoon is needed, you don't want to get your fingers too close to that steam!

Another asterism, although less famous, is the Terebellum.  The Terebellum is a quadrilateral pattern on the easternmost regions of the constellation.  They are close together in the sky but in reality they are not gravitationally linked at all.

There are many famous deep sky objects found within the boundaries of the constellation.  Fifteen Messier objects call this region of the sky home.  The table below highlights these objects.

Messier	Name/Type
M8	The Lagoon Nebula (Emission Nebula)
M17	The Omega Nebula, The Swan Nebula, The Checkmark Nebula (Emission Nebula)
M18	Open Cluster
M20	The Trifid Nebula (Open Cluster, Emission Nebula, Reflection Nebula, Dark Nebula)
M21	Open Cluster
M22	Globular Cluster
M23	Open Cluster
M24	The Sagittarius Star Cloud (Open Cluster)
M25	Open Cluster
M28	Globular Cluster
M54	Globular Cluster
M55	Globular Cluster
M69	Globular Cluster
M70	Globular Cluster
M75	Globular Cluster

This rich area of the sky is filled with many open clusters and globular clusters.  There are also several notable nebulae that have been viewed over the centuries.  I have viewed the deep sky objects on this list and I can vouch for their beauty.  I will revisit this area of the sky each Summer.