How to Find the Sagittarius Constellation in the Night Sky

Northern hemisphere summer constellations.
Northern hemisphere summer skies, looking south.

Carolyn Collins Petersen

The skies of July and August provide an excellent view of the constellation Sagittarius. Easy to spot and filled with fascinating deep-sky objects, Sagittarius is an ideal subject of study for stargazers and astronomers alike.

The constellation Sagittarius is often referred to as a teapot because of its appearance: the main boxy shape is the body of the teapot, from which a handle and a spout extend outward. Some observers add that the Milky Way appears to be rising up out of the spout like steam.

Finding the Sagittarius Constellation

In the northern hemisphere, Sagittarius reaches its highest point in the southern part of the sky during July and August and into early September. Sagittarius is also visible high in the northern part of the sky for regions south of the equator.

Sagittarus has such a distinctive shape that it's not too hard to spot in the sky. Simply look for the teapot shape next to the curved body of Scorpius the Scorpion. Not only are these constellations filled with fascinating celestial bodies to observe, they are also on either side of the core of our galaxy, where the black hole Sgr A* lives.

scorp_sag.jpg
A chart of the sky containing Scorpius and Sagittarius. Ross 154 is a faint star in Sagittarius. Carolyn Collins Petersen

All About Scorpius

Sagittarius is best-known as the figure of a cosmic archer, although the Greeks saw it as a starry representation of a mythical creature called a centaur.

Alternatively, some mythology identifies Sagittarius as the son of Pan, the god who created archery. His name was Crotus, and he was put into the sky by the god Zeus so that everyone could see how archery worked. (However, most viewers don't see an archer when they look at Sagittarius—the teapot shape is far easier to identify.)

The Stars of the Scorpius Constellation

Sagittarius Constellation chart
The entire constellation of Sagittarius shown with IAU boundaries and the brightest stars that make up the pattern.  IAU/Sky & Telescope

The brightest star in the constellation Sagittarius is called Kaus Australis (or Epsilon Sagittarii). The second-brightest is Sigma Sagittarii, with a common name of Nunki. Sigma (Nunki) was one of the stars that the Voyager 2 spacecraft used for navigation as it was traveling to the outer solar system to study the gas giant planets. 

There are eight bright stars that make up the "teapot" shape of the main constellation. The rest of the constellation as outlined by the IAU boundaries has a couple of dozen more stars. 

Sagittarius constellation
Sagittarius constellation is outlined by eight bright stars, and scattered among them are globular clusters (yellow circles), open clusters (yellow broken line circles), and nebulae (squares). It's best to search this area with a good pair of binoculars just to get an idea of the many fascinating objects in the Sagittarius region.  Carolyn Collins Petersen

Selected Deep Sky Objects in Constellation Sagittarius

Sagittarius is right on the plane of the Milky Way and its teapot spout points almost directly to the center of our galaxy. Because the galaxy is so well-populated in this part of the sky, observers can spot many star clusters, including a number of globular clusters and open star clusters. Globulars are spherical-shaped collections of stars, many much older than the galaxy itself. Open star clusters are not as tightly gravitationally bound as the globulars.

Sagittarius also contains some lovely nebulae: clouds of gas and dust lit up by radiation from nearby stars. The most prominent objects to search out in this area of the sky are the Lagoon Nebula, the Trifid Nebula, and the globular clusters M22 and M55. 

Nebulae in Sagittarius

Because we look at the galaxy from inside, it's very common to see clouds of gas and dust in the plane of the Milky Way. This is especially true in Sagittarius. The Lagoon and Trifid Nebulae are the easit to spot, although they can generally only be seen well with binoculars or a small telescope. Both of these nebulae contain regions where star formation is actively taking place. Astronomers see both newborn stars as well as protostellar objects in these regions, which helps them track the process of starbirth.

The Trifid is also known as Messier 20 and has been studied by many ground-based observatories as well as Hubble Space Telescope. It will look somewhat dim but should be easy to spot in a small telescope. Its name comes from the fact that it looks like a little pool next to the brighter regions of the Milky Way. The Trifid looks like it has three "lobes" connected together. They lie just over four thousand light-years away from us. 

The Trifid Nebula in Sagittarius.
The Trifid Nebula in full glorious color provided by the European Southern Observatory. Smaller telescopes will not show these colors, but a long-exposure photograph will.  European Southern Observatory

Globular Clusters in Sagittarius

Globular clusters are satellites of the Milky Way Galaxy. They often contain hundreds, thousands, or sometimes millions of stars, all tightly bound together by gravity. M22 (which is the 22nd objects in Charles Messier's list of "Faint fuzzy objects" that he compiled in the 18th century), was first discovered in 1665 and contains about 300,000 stars all packed together in a region of space about 50 light-years across. 

Messier 22 in Sagittarius
This view of the globular cluster M22 in Sagittarius was taken using an amateur telescope.  Hunter Wilson, via Creative Commons Attribution Share-Alike 3.0

Another interesting globular cluster is also in Sagittarius. It's called M55, and was discovered in 1752. It contains just under 300,000 stars all gathered into an area bout 48 light-years across. It lies nearly 18,000 light-years away from us. Search out Sagittarius for other clusters and nebulae, especially using a pair of binoculars or a small telescope.