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Sagittarius (constellation)

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Sagittarius is a prominent constellation located in the Southern celestial hemisphere. It is one of the 88 modern constellations used by astronomers today. It was also one of the 48 constellations listed by the astronomer Ptolemy in the 2nd century.

Sagittarius symbol (Moskowitz, fixed width)
Sagittarius symbol (Moskowitz, fixed width)

The name Sagittarius is Latin for "archer." In many depictions, it represents a centaur, a creature that is half man and half horse, drawing a bow. Because it is a zodiac constellation, it holds a special place in astronomy.

SagittariusCC
SagittariusCC

It sits between Scorpius and Ophiuchus to the west, and Capricornus and Microscopium to the east.

Many observers find Sagittarius by looking for a recognizable pattern of stars called an asterism. This specific pattern is known as "the Teapot."

Sagittarius-teapot-asterism
Sagittarius-teapot-asterism

The stars Delta Sagittarii, Epsilon Sagittarii, Zeta Sagittarii, and Phi Sagittarii form the main body of the pot. Lambda Sagittarii serves as the lid, while Gamma2 Sagittarii marks the tip of the spout. The stars Sigma Sagittarii and Tau Sagittarii form the handle. Under dark skies, the Large Sagittarius Star Cloud appears to rise from the spout like steam from a boiling kettle. This cloud is a very dense region of the Milky Way galaxy.

The stars in this asterism actually form the components of the archer's weapon. Delta Sagittarii is called Kaus Media, meaning the "center of the bow." Gamma2 Sagittarii is named Alnasl, which is the Arabic word for "arrowhead." The arrow appears to point directly at the heart of Scorpius, which is the reddish star Antares. Lambda Sagittarii and Epsilon Sagittarii are known as Kaus Borealis and Kaus Australis, representing the northern and southern portions of the bow.

Sidney Hall - Urania's Mirror - Sagittarius and Corona Australis, Microscopium, and Telescopium
Sidney Hall - Urania's Mirror - Sagittarius and Corona Australis, Microscopium, and Telescopium

This connection between the stars and the archer imagery creates a clear visual story in the night sky.

History and star names provide a deep connection to the past. The star Sigma Sagittarii, also called Nunki, has a Babylonian name. It is thought to represent the sacred city of Eridu on the Euphrates. This makes Nunki the oldest star name currently in use. The constellation's position relative to the Sun changes over long periods due to a process called precession. In classical antiquity, the Sun was in Capricorn during the December solstice. By the Roman Empire, precession had shifted this position to Sagittarius. By approximately 2700 AD, the Sun will be located in Scorpius during the December solstice.

Sagittarius is a vital region for studying the structure of our galaxy. The center of the Milky Way lies in the westernmost part of the constellation.

Within this region lies Sagittarius A*, a supermassive black hole. Astronomers estimate this black hole has a mass of 2.6 million solar masses. Because the Milky Way is so dense here, the area contains many star clusters and nebulae. One such cluster is the Small Sagittarius Star Cloud, or Messier 24. This cloud has a depth of 10,000 to 16,000 light-years and contains the dense star cluster NGC 6603.

Several famous nebulae are located within the boundaries of Sagittarius. The Lagoon Nebula, or Messier 8, is an emission nebula located 5,000 light-years away. It measures 140 light-years by 60 light-years and has a bright magnitude of 3.0. It was discovered by John Flamsteed, Guillaume Le Gentil, and Charles Messier at different times. The Omega Nebula is another bright object, sometimes called the Swan Nebula. It is located 4,890 light-years from Earth.

Omega Nebula
Omega Nebula

The Trifid Nebula, or Messier 20, is also nearby. It is an emission nebula where hydrogen is ionized by a central triple star, creating a pink interior and blue exterior.

Other deep-sky objects add to the complexity of this region. Messier 54 was the first globular cluster discovered outside the Milky Way.

Messier 54 HST
Messier 54 HST

Astronomers also study "Baade's Window," an area with very little dust. This allows them to see objects closer to the galactic center, such as the globular clusters NGC 6522 and NGC 6528. These clusters are located between 20,000 and 24,000 light-years from Earth. Even more distant is the globular cluster NGC 6638, which sits about 26,000 light-years away. These objects help scientists map the vast distances and structures within our galactic neighborhood.

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🖼️ Images & Media (9)
File:Sagittarius symbol (Moskowitz, fixed width).svg
Sagittarius symbol (Moskowitz, fixed width).svg
File:Sagittarius-teapot-asterism.jpg
Sagittarius-teapot-asterism.jpg
File:Sagittarius region .jpg
Sagittarius region .jpg
File:SagittariusCC.jpg
SagittariusCC.jpg
File:Large Sagittarius star cloud.jpg
Large Sagittarius star cloud.jpg
File:Omega Nebula.jpg
Omega Nebula.jpg
File:Messier 54 HST.jpg
Messier 54 HST.jpg
File:Sidney Hall - Urania's Mirror - Sagittarius and Corona Australis, Microscopium, and Telescopium.png
Sidney Hall - Urania's Mirror -...
File:Terebellum asterism.png
Terebellum asterism.png
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