Sagittarius is one of the constellations of the zodiac. It is one of the 48 constellations listed by the 2nd-century astronomer Ptolemy and remains one of the 88 modern constellations. Its name is Latin for the archer, and its symbol is (Unicode U+2650 ♐), a stylized arrow. Sagittarius is commonly represented as a centaur pulling back a bow. It lies between Scorpius and Ophiuchus to the west and Capricornus and Microscopium to the east.
|Area||867 sq. deg. (15th)|
|Main stars||12, 8|
|Stars with planets||32|
|Stars brighter than 3.00m||7|
|Stars within 10.00 pc (32.62 ly)||3|
|Brightest star||ε Sgr (Kaus Australis) (1.79m)|
|Visible at latitudes between +55° and −90°.|
Best visible at 21:00 (9 p.m.) during the month of August.
As seen from the northern hemisphere, the constellation's brighter stars form an easily recognizable asterism known as "the Teapot". The stars δ Sgr (Kaus Media), ε Sgr (Kaus Australis), ζ Sgr (Ascella), and φ Sgr form the body of the pot; λ Sgr (Kaus Borealis) is the point of the lid; γ2 Sgr (Alnasl) is the tip of the spout; and σ Sgr (Nunki) and τ Sgr the handle. These same stars originally formed the bow and arrow of Sagittarius.
To complete the teapot metaphor, under good conditions, a particularly dense area of the Milky Way can be seen rising in a north-westerly arc above the spout, like a puff of steam rising from a boiling kettle.
The constellation as a whole is often depicted as having the rough appearance of a stick-figure archer drawing its bow, with the fainter stars providing the outline of the horse's body. Sagittarius famously points its arrow at the heart of Scorpius, represented by the reddish star Antares, as the two constellations race around the sky. Following the direct line formed by Delta Sagittarii (δ Sgr) and Gamma2 Sagittarii (γ2 Sgr) leads nearly directly to Antares. Fittingly, Gamma2 Sagittarii is Alnasl, the Arabic word for "arrowhead", and Delta Sagittarii is called Kaus Media, the "center of the bow," from which the arrow protrudes. Kaus Media bisects Lambda Sagittarii (λ Sgr) and Epsilon Sagittarii (ε Sgr), whose names Kaus Borealis and Kaus Australis refer to the northern and southern portions of the bow, respectively.
α Sgr (Rukbat, meaning "the archer's knee") despite having the "alpha" designation, is not the brightest star of the constellation, having a magnitude of only 3.96. It is towards the bottom center of the map as shown. Instead, the brightest star is Epsilon Sagittarii (ε Sgr) ("Kaus Australis," or "southern part of the bow"), at magnitude 1.85.
Sigma Sagittarii (σ Sgr) ("Nunki") is the constellation's second-brightest star at magnitude 2.08. Nunki is a B2V star approximately 260 light years away. "Nunki" is a Babylonian name of uncertain origin, but thought to represent the sacred Babylonian city of Eridu on the Euphrates, which would make Nunki the oldest star name currently in use.
Eta Sagittarii (η Sgr) is a double star with component magnitudes of 3.18 and 10, while Pi Sagittarii (π Sgr) ("Albaldah") is actually a triple system whose components have magnitudes 3.7, 3.8, and 6.0.
The Bayer designation Beta Sagittarii (Beta Sgr, β Sagittarii, β Sgr) is shared by two star systems, β¹ Sagittarii, with apparent magnitude 3.96, and β² Sagittarii, magnitude 7.4. The two stars are separated by 0.36° in the sky and are 378 light years from earth. Beta Sagittarii, located at a position associated with the forelegs of the centaur, has the traditional name Arkab, meaning "achilles tendon."
Nova Sagittarii 2015 No. 2 was discovered on 15 March 2015, by John Seach of Chatsworth Island, NSW, Australia. It lies near the center of the constellation. It reached a peak magnitude of 4.3 before steadily fading.
Sagittarius contains several well-known nebulae, including the Lagoon Nebula (Messier 8), near λ Sagittarii; the Omega Nebula (Messier 17), near the border with Scutum; and the Trifid Nebula (Messier 20), a large nebula containing some very young, hot stars.
In addition, several other nebulae have been located within Sagittarius and are of interest to astronomy.
In 1999 a violent outburst at V4641 Sgr was thought to have revealed the location of the closest known black hole to Earth, but later investigation increased its estimated distance by a factor of 15. The complex radio source Sagittarius A is also in Sagittarius, near its western boundary with Ophiuchus. Astronomers believe that one of its components, known as Sagittarius A*, is associated with a supermassive black hole at the center of the galaxy, with a mass of 2.6 million solar masses. The Sagittarius Dwarf Elliptical Galaxy is located just outside the Milky Way.
Baade's Window is an area with very little obscuring dust that shows objects closer to the Milky Way's center than would normally be visible. NGC 6522, magnitude 8.6, and NGC 6528, magnitude 9.5, are both globular clusters visible through Baade's Window. 20,000 and 24,000 light-years from Earth, with Shapley classes of VI and V respectively, both are moderately concentrated at their cores. NGC 6528 is closer to the galactic core at an approximate distance of 2,000 light-years.
2MASS-GC02, also known as Hurt 2, is a globular cluster at a distance of about 16 thousand light-years from Earth. It was discovered in 2000 by Joselino Vasquez, and confirmed by a team of astronomers under the leadership of R. J. Hurt at 2MASS.
The space probe New Horizons is moving on a trajectory out of the Solar System as of 2016 that places the probe in front of Sagittarius as seen from the Earth. New Horizons will exhaust its radioisotope thermoelectric generator long before it reaches any other stars.
The Wow! signal was a strong narrowband radio signal that appeared to have come from the direction of Sagittarius.
The Babylonians identified Sagittarius as the god Nergal, a strange centaur-like creature firing an arrow from a bow. It is generally depicted with wings, with two heads, one panther head and one human head, as well as a scorpion's stinger raised above its more conventional horse's tail. The Sumerian name Pabilsag is composed of two elements – Pabil, meaning 'elder paternal kinsman' and Sag, meaning 'chief, head'. The name may thus be translated as the 'Forefather' or 'Chief Ancestor'. The figure is reminiscent of modern depictions of Sagittarius.
In Greek mythology, Sagittarius is usually identified as a centaur: half human, half horse. However, perhaps due to the Greeks' adoption of the Sumerian constellation, some confusion surrounds the identity of the archer. Some identify Sagittarius as the centaur Chiron, the son of Philyra and Cronus, who was said to have changed himself into a horse to escape his jealous wife, Rhea, and tutor to Jason. As there are two centaurs in the sky, some identify Chiron with the other constellation, known as Centaurus. Or, as an alternative tradition holds, that Chiron devised the constellations Sagittarius and Centaurus to help guide the Argonauts in their quest for the Golden Fleece.
A competing mythological tradition, as espoused by Eratosthenes, identified the Archer not as a centaur but as the satyr Crotus, son of Pan, who Greeks credited with the invention of archery. According to myth, Crotus often went hunting on horseback and lived among the Muses, who requested that Zeus place him in the sky, where he is seen demonstrating archery.
The arrow of this constellation points towards the star Antares, the "heart of the scorpion", and Sagittarius stands poised to attack should Scorpius ever attack the nearby Hercules, or to avenge Scorpius's slaying of Orion.
As of 2002, the Sun appears in the constellation Sagittarius from 18 December to 18 January. In tropical astrology, the Sun is considered to be in the sign Sagittarius from 22 November to 21 December, and in sidereal astrology, from 16 December to 14 January.
56 Sagittarii (56 Sgr) is a class K1III (orange giant) star in the constellation Sagittarius. Its apparent magnitude is 4.87 and it is approximately 208 light years away based on parallax.HD 164604
HD 164604 is a K dwarf star in the Sagittarius constellation. It has a single gas giant planet detected by the Magellan Planet Search Program in 2010.HD 169830
HD 169830 is a yellow-white dwarf star (spectral type F9V) in the constellation of Sagittarius, 118.46 light years from the Solar System. It is known to be orbited by two large Jupiter-like planets.HD 187085
HD 187085 is a yellow main sequence star about 147 light-years away in the constellation Sagittarius. It is estimated to be younger than our Sun, at about 3.3 (± 1) billion years old, and more massive at 1.22 solar masses.
In 2006, an extrasolar planet was announced orbiting HD 187085.HD 190647
HD 190647 is a yellow subgiant star located approximately 177 light years away in the constellation of Sagittarius. The apparent magnitude is 8 and absolute magnitude is 4. It is also called HIP 99115. In 2007, a planet was found to be orbiting the star.MOA-2007-BLG-192L
MOA-2007-BLG-192L is a low-mass red dwarf star or brown dwarf, approximately 3,000 light-years away in the constellation of Sagittarius. It is estimated to have a mass approximately 6% of the Sun's. In 2008, an Earth-sized extrasolar planet was announced to be orbiting this object.MOA-2007-BLG-400L
MOA-2007-BLG-400L is a star located approximately 20000 light-years away in the constellation of Sagittarius. This star is presumed to be a red dwarf with a spectral type of M3V, based on its mass of 0.35 MS.MOA-2009-BLG-387L
MOA-2009-BLG-387L is a red dwarf in the Sagittarius constellation that is host to the planet MOA-2009-BLG-387Lb. The star is estimated to be nearly 20,000 light years away and approximately one fifth the mass of the Sun, although large confidence intervals exist, reflecting the uncertainties in both the mass and distance. The star drew the attention of astronomers when it became the lens of gravitational microlensing event MOA-2009-BLG-387L, in which it eclipsed a background star and created distorted caustics, an envelope of reflected or refracted light rays. Analysis of the caustic events and of follow-up observational data led to the planet's discovery, which was reported in February 2011.Nova Sagittarii 1898
Nova Sagittarii 1898 (also called V1059 Sagittarii) was a nova, which lit up in 1898 in the constellation Sagittarius. Nova Sagittarii 1898 reached magnitude 4.5.OGLE-TR-56
OGLE-TR-56 is a dim, distant, magnitude 17 Sun-like star located approximately 1500 parsecs away in the constellation of Sagittarius.
This star is listed as an eclipsing type variable star with the eclipse due to the passage of the planet as noted in the discovery papers.V1017 Sagittarii
V1017 Sagittarii is a cataclysmic variable star system in the constellation Sagittarius. It first erupted in 1919, reaching magnitude 7. Its other eruptions in 1901, 1973 and 1991 only reached magnitude 10, leading it to be reclassified from a recurrent nova to a dwarf nova.V4024 Sagittarii
V4024 Sagittarii is a star in the constellation Sagittarius. Its apparent magnitude is 5.56.V4641 Sagittarii
V4641 Sagittarii (V4641 Sgr) is a variable X-ray binary star system in the constellation Sagittarius. It is the source of one of the fastest superluminal jets in the Milky Way galaxy.
In 1999 a violent X-ray outburst revealed it to contain a black hole. At the time, it was considered to be the closest known black hole to Earth, at a distance of approximately 1,600 light-years (490 pc). Later observations showed it to be at least 15 times farther away.V4650 Sagittarii
V4650 Sagittarii (qF362) is a luminous blue variable star (LBV) in the constellation of Sagittarius. Located some 25,000 light years away, the star is positioned on the edge of a starburst cluster known as the Quintuplet cluster.V4743 Sagittarii
V4743 Sagittarii (V4743 Sgr) was a bright nova in the constellation Sagittarius which peaked at magnitude of 5.0 in September 2002.V5668 Sagittarii
V5668 Sagittarii was a bright nova in the constellation Sagittarius discovered by John Seach of Chatsworth Island, New South Wales, Australia on March 15 and which peaked at magnitude of 4.3 in late March 2015.V725 Sagittarii
V725 Sagittarii (V725 Sgr) is a semiregular pulsating variable star in the constellation of Sagittarius. As recently as a century ago, it was a Population II Cepheid; its transformation was documented by Henrietta Swope beginning in 1937, and is one of the most exciting and instructive events in variable-star astronomy.W33A
W33A is a protostar located approximately 12,000 light-years away from Earth, in the constellation Sagittarius. As a star in the early stages of formation, so has attracted the interest of astronomers, who observed that while the protostar is accumulating material from surrounding clouds of gas and dust, it is simultaneously ejecting fast moving jets of particles from its north and south poles.WR 102ea
WR 102ea is a Wolf–Rayet star in the Sagittarius constellation. It is the second most luminous star in the Quintuplet cluster after WR 102hb. With a luminosity of 2,500,000 times solar, it is also one of the most luminous stars known. Despite the high luminosity it can only be observed at infra-red wavelengths due to the dimming effect of intervening dust on visual light.
It is an evolved massive star which has an emission line spectrum from a strong stellar wind caused by high luminosity and the presence of elements heavier than hydrogen in the photosphere. The spectrum is dominated by ionised helium and nitrogen lines due to convectional and rotational mixing of fusion products to the surface of the star. However it is still in a core hydrogen burning phase and hydrogen lines are also visible in the spectrum, in contrast to WN stars without hydrogen which are older, less massive, and less luminous. Despite being a relatively unevolved star, WR 102ea has lost over half its mass already.
Stars of Sagittarius