Tau Sagittarii
Encyclopedia
Tau Sagittarii is a star
in the constellation
Sagittarius
, 120 light years from Earth. In ancient Chinese astronomy, it is the 5th star of 6 stars in the Dipper
or 'South Dipper' mansion of the Black Tortoise of the North. Tau Sagittarii is located on the "handle" between Ascella (Zeta Sgr) and Nunki (Sigma Sgr) on the teapot
asterism
.
It is a spectral type
K1 or K2 giant
, 1.5 - 2 Solar masses, with an apparent magnitude
of +3.32. It is slightly cooler than our sun, of a light orange color. It is a suspected double star although no companion has been confirmed yet. A lower metal content (Fe to H ratio is 70%) and a high velocity (64 km/s, 4x the local average) relative to the Sun suggest the star is a visitor from a different part of the Galaxy.
It is also the closest visible star in the night sky to the origin of the 1977 Wow! signal
, the only radio signal that has been received that may be a sign of extraterrestrial intelligence.
The location of the signal was, at (epoch
J2000.0):
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
Sagittarius
Sagittarius (constellation)
Sagittarius is a constellation of the zodiac, the one containing the galactic center. Its name is Latin for the archer, and its symbol is , a stylized arrow. Sagittarius is commonly represented as a centaur drawing a bow...
, 120 light years from Earth. In ancient Chinese astronomy, it is the 5th star of 6 stars in the Dipper
Dipper (Chinese constellation)
The Dipper mansion is one of the Twenty-eight mansions of the Chinese constellations. It is one of the northern mansions of the Black Tortoise.-Asterisms:-Stars:* ζ Sgr* τ Sgr* σ Sgr* φ Sgr* λ Sgr* μ Sgr...
or 'South Dipper' mansion of the Black Tortoise of the North. Tau Sagittarii is located on the "handle" between Ascella (Zeta Sgr) and Nunki (Sigma Sgr) on the teapot
Teapot
A teapot is a vessel used for steeping tea leaves or a herbal mix in near-boiling water. Tea may be either in a tea bag or loose, in which case a tea strainer will be needed, either to hold the leaves as they steep or to catch the leaves inside the teapot when the tea is poured...
asterism
Asterism (astronomy)
In astronomy, an asterism is a pattern of stars recognized on Earth's night sky. It may form part of an official constellation, or be composed of stars from more than one. Like constellations, asterisms are in most cases composed of stars which, while they are visible in the same general direction,...
.
It is a spectral type
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
K1 or K2 giant
Giant star
A giant star is a star with substantially larger radius and luminosity than a main sequence star of the same surface temperature. Typically, giant stars have radii between 10 and 100 solar radii and luminosities between 10 and 1,000 times that of the Sun. Stars still more luminous than giants are...
, 1.5 - 2 Solar masses, with an apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
of +3.32. It is slightly cooler than our sun, of a light orange color. It is a suspected double star although no companion has been confirmed yet. A lower metal content (Fe to H ratio is 70%) and a high velocity (64 km/s, 4x the local average) relative to the Sun suggest the star is a visitor from a different part of the Galaxy.
It is also the closest visible star in the night sky to the origin of the 1977 Wow! signal
Wow! signal
The Wow! signal was a strong narrowband radio signal detected by Dr. Jerry R. Ehman on August 15, 1977, while working on a SETI project at the Big Ear radio telescope of The Ohio State University then located at Ohio Wesleyan University's Perkins Observatory, Delaware, Ohio. The signal bore...
, the only radio signal that has been received that may be a sign of extraterrestrial intelligence.
The location of the signal was, at (epoch
Epoch (astronomy)
In astronomy, an epoch is a moment in time used as a reference point for some time-varying astronomical quantity, such as celestial coordinates, or elliptical orbital elements of a celestial body, where these are subject to perturbations and vary with time...
J2000.0):
- Right ascensionRight ascensionRight ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
(on the positive horn): 19h25m31s +/- 10s - Right ascensionRight ascensionRight ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
(on the negative horn): 19h28m22s +/- 10s - DeclinationDeclinationIn astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
(the same for both horns): -26d57m +/- 20m