VX Sagittarii is a late-type red supergiant

Red supergiant

Red supergiants are supergiant stars of spectral type K or M. They are the largest stars in the universe in terms of volume, although they are not the most massive...

 star (likely even a red hypergiant

Hypergiant

A hypergiant is a star with a tremendous mass and luminosity, showing signs of a very high rate of mass loss.-Characteristics:...

) located more than 1.7 kiloparsec away from Sun in the constellation of 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...

.

Stellar characteristics

It is classed as a cool semiregular variable with a pulsational period of 732 day

Day

A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun...

s and spectral type varying between M5.5 (close to visual maximum) and M9.8 (at minimum light). The effective temperature spans between a minimum of 2,400 and a maximum of 3,300 kelvin degrees. Average temperature is estimated 2,900 K . Stellar behaviour mostly resembles that of Mira

Mira

Mira also known as Omicron Ceti , is a red giant star estimated 200-400 light years away in the constellation Cetus. Mira is a binary star, consisting of the red giant Mira A along with Mira B. Mira A is also an oscillating variable star and was the first non-supernova variable star discovered,...

-type pulsating giants and shows hints of molecular water layers and SiO masers in the atmosphere.