Summer Constellation Spotlight: Sagittarius

One of the most famous constellations in the zodiac, Sagittarius, the Archer, is shown as a centaur—half man, half horse—poised to shoot with his bow and arrow. It is easy to find thanks to its brightest stars, which seem to form a “teapot.” Because Sagittarius lies in the Milky Way and is in the same direction as the Galactic Center, it contains a variety of well-known deep sky objects, including dwarf galaxies, nebulae, star clouds, and globular and open star clusters—many of which are visible to the naked eye, binoculars or telescopes.

Sagittarius is one of the 48 constellations listed by the 2nd-century astronomer Ptolemy and remains one of the 88 modern constellations today. The best time to view it is during the summer months, particularly in mid-August, when it is at its highest point in the night sky. You’ll find it following Scorpius just below the ecliptic. Sagittarius offers plenty to explore, so let’s get to know a few of its most popular targets.

Kaus Australis

Kaus Australis, Epsilon Sagittarii, is the brightest star in the constellation, with an apparent magnitude of +1.85. It’s a binary star system located approximately 143 light-years away from Earth. The primary star in the system is a blue giant, while the secondary star is a white dwarf. Kaus Australis is derived from the Arabic phrase “kaus al-jenūb,” which means “the bow of the south,” the southern tip of the archer’s “bow.”

Sigma Sagittarii

Sigma Sagittarii, also known as Nunki, is the second brightest star in Sagittarius, shining at an apparent magnitude of +2.05. Due to its brightness and position, it is a significant navigation star. Sigma Sagittarii is a young blue-white star about 228 light years away with a mass 7.8 times that of the Sun with a luminosity 3,300 times greater.

Sagittarius A*

Sagittarius A*, or Sgr A*, is a notable feature of the Sagittarius constellation. However, it is not a star—it’s a supermassive black hole at the center of our Milky Way galaxy, the Galactic Center. Although the black hole is immense, we can’t see it with the naked eye. Astronomers can only observe it using high-powered telescopes and special techniques to detect the radio waves it emits.

Sagittarius is easily recognizable due to its asterism of stars, which look more like a “teapot” than a centaur. The galactic center Sagittarius A* is near the spout’s top.

Lagoon Nebula (Messier 8)

The Lagoon Nebula (Messier 8) gets its name from a dark, winding dust lane that runs through the nebula. It is a large gas cloud (approximately 130 light-years across) near the center of our Milky Way Galaxy, about three times the size of the full Moon. It is bright enough to be seen with the naked eye from a dark sky, but using a binocular or telescope provides astonishing views. A bright open cluster, NGC 6530, comprised of young, hot, blue stars, lies within the nebula and is easily visible. M8 is an emission nebula. Like its wintertime counterpart, the Orion Nebula, M8 is a star-forming region—a stellar nursery where young stars are born.

Eagle Nebula (Messier 16)

Also known as Messier 16, the Eagle Nebula is one of the most popular celestial targets in the Summer skies for backyard stargazers. Located in the direction of Serpens the Serpent, it is one of the most famous celestial targets due to its appearance as a spread-out eagle and because of its iconic towering structures, the "Pillars of Creation." This nebula is an active star-forming region of gas and dust. The Eagle Nebula is a relatively young open star cluster with areas of dark nebulae that do not shine any light themselves but rather block light from other sources. In 2017, the Hubble Space Telescope captured a stunning image of the Pillars of Creation that remains one of the most spectacularly detailed celestial images today.

Swan Nebula (Messier 17)

Also known as the Swan Nebula (Messier 17), the Omega Nebula shines at an apparent magnitude of 6.0, so you will get the best views in binoculars or a low-power telescope. It is near another prominent object, the Eagle Nebula. Both nebulae are near the center of our Milky Way galaxy, where many other bright star clusters and nebulae reside. Look for the teapot asterism in Sagittarius and draw an imaginary line from the bottom star Kaus Australis to Kaus Media. Then, move up about 15 degrees to M17. Both M17 and M16 are highest in the sky in late August evenings.

Open Star Cluster (Messier 18)

Sometimes called NGC 6613, the Black Swan Cluster, M18, is an open star cluster between the Swan Nebula (M17) and the Sagittarius Star Cloud (M24). It contains a group of around 20 young, bright stars approximately 4,900 light years from Earth. Charles Messier discovered the cluster in 1764. It has an apparent magnitude of 7.5, making it well within range of binoculars and telescopes from a dark sky location.

Trifid Nebula (Messier 20)

Discovered by Charles Messier in 1764, the Trifid Nebula (Messier 20) is a star-forming region located near the center of the Milky Way and just two degrees northwest of the Lagoon Nebula. Both objects are often imaged together in the same field of view. M20 has an apparent magnitude of 6.3 and appears as a fuzzy patch of light in binoculars. Its name means 'three-lobe.' The Trifid is easy to see in a telescope from a dark sky location. Some sports fans have noted that the three dark dust lanes resemble Nike's "Air Jordan" logo when viewed from a certain angle.

Open Star Cluster (Messier 21)

Messier 21, also known as NGC 6531, is a beautiful open star cluster near the Trifid Nebula (M20). Charles Messier discovered it in 1764. It lies approximately 3,900 light years from Earth. With an apparent magnitude of 6.5, it is visible in binoculars and small telescopes from dark skies. M21 contains about 57 stars.

Sagittarius Cluster (Messier 22)

Messier 22, also known as the Sagittarius Cluster or NGC 6656, is a bright globular cluster with an apparent magnitude of 5.1, making it one of the more remarkable objects visible from the Northern and Southern Hemispheres. German astronomer Abraham Ihle discovered it in 1665. M22 lies approximately 10,600 light-years from Earth. It contains around 70,000 stars. It is one of the few globular clusters known to contain a planetary nebula.

Open Star Cluster (Messier 23)

Messier 23, also known as NGC 6494, is a beautiful open star cluster near the Teapot asterism. Charles Messier discovered it in 1764. M23 lies 2,150 light years from Earth. It shines at an apparent magnitude of 6.9, making it visible in binoculars and small telescopes. The cluster contains about 176 stars.

Sagittarius Star Cloud (Messier 24)

The Sagittarius Star Cloud, also known as Delle Caustiche, is striking when viewed through binoculars or a telescope. It is often described as a “carpet of stellar jewels” due to its dense and bright star field. It lies approximately 10,000 light years from Earth. Notably, it includes two prominent dark nebulae, Barnard 92 and Barnard 93. Both appear as dark patches against a bright backdrop of stars.

Open Star Cluster (Messier 25)

Also known as IC 4725, Messier 25 is a prominent open star cluster near the Teapot asterism, approximately 2,000 years from Earth. With an apparent magnitude of 4.6, it is within the range of naked eye visibility from a dark sky in good seeing conditions. M25 contains around 600 stars.

Globular Star Cluster (Messier 28)

Also known as NGC 6626, M28 is a globular cluster discovered by Charles Messier in 1764. Its distance from Earth is approximately 18,000 light years. The cluster shines at an apparent magnitude of 7.7, making it visible in binoculars and telescopes from a dark sky. Astronomers estimate that M28 contains tens of thousands of stars.

Globular Star Cluster (Messier 54)

Also known as NGC 6715, M54 is a unique globular cluster. It was the first globular cluster to be discovered that belonged to another galaxy, the Sagittarius Dwarf Elliptical Galaxy (SagDEG). It is suspected to have a black hole at its core. M54 was discovered in 1778 by Charles Messier. It lies approximately 87,000 light years from Earth and has an apparent magnitude of 7.6, making it visible in binoculars and telescopes, especially from dark skies.

Globular Star Cluster (Messier 55)

Also known as NGC 6809 or the Summer Rose Star, M55 was discovered by French astronomer Nicolas Louis de Lacaille in 1752 but cataloged by Charlies Messier in 1778. It is a globular cluster containing about 100,000 and 55 variable stars. One of its notable features is that it lacks a dense core, making the stars appear more evenly distributed compared to other globular clusters. M55 lies approximately 17,600 light years from Earth with an apparent magnitude of 6.3. It is visible in binoculars and telescopes from a dark sky.

Barnard’s Galaxy (NGC 6822)

Barnard’s galaxy, also known as NGC 6822, IC 4895, or Caldwell 57, is a barred irregular galaxy that is part of the Local Group of galaxies and is similar in composition and structure to the Small Magellanic Cloud. Edward Emerson Barnard discovered it in 1884. The galaxy lies approximately 1.6 million light-years from Earth. With an apparent magnitude of 9.3, it is visible in small aperture telescopes under dark sky conditions.