Astronomers have been making remarkable progress in discovering far away stars that seem to be of impressive size even though there are important uncertainties in values and sizes also coming from the way that this distance influences the size measurements. Moreover, many such stars are surrounded by extended atmospheres or pulsate making radius determination even more difficult. But even so, here is a list of the 10 largest stars in radius that have been discovered thus far:

  1. NML Cygni

This red hypergiant star (hypergiants are stars with enormous luminosity and mass, that have a high rate of mass loss) is currently the largest known star and one of the most luminous cool hypergiants. In radius, NML Cygni is approximately 1650 times larger than our Sun and it is located about 5300 Light Years from Earth. Surrounding the star, there is a dusty environment composed of 2 discrete envelopes as well as an asymmetric, bean –shaped nebula that coincides with the distribution of water vapor marsers (these are spectral line emissions that arise in stellar atmospheres). Acording to astronomers, it is an oxygen-rich star that has a unique location within our galaxy and does not dominate its interstellar environment.


  1. WHO G64

Located in the Large Magellanic Cloud (a nearby galaxy 163000 Light years from the Earth), this red hypergiant is, at 1540 times the radius of the Sun, the largest star in the Large Magellanic Cloud and one of the largest in the known universe. Sadly, because of the distance, the solar masses of dust and the visual faintness, other physical parameters are poorly known.

This image from NASA's Spitzer Space Telescope shows infant stars "hatching" in the head of the hunter constellation, Orion.

  1. VX Sagittarii

This red supergiant is located about 1.5 kiloparsec away from the sun and is a pulsating variable star which means that its brightness ( apparent magnitude) fluctuates as seen from Earth. It has a pulsational period is of 732 days and luminosity class 1a (bright supergiant). Because of this pulsation, the radius of the star cannot be accurately measured, therefore the actual radius ( 1520 times of that of our Sun) is an estimate that takes into consideration the peak luminosity and its relationship to peak temperature, in this case coincident, although astronomers believe that peak luminosity is found at a lower temperature in pulsating stars and that therefore the peak radius is likely larger.


  1. KW Sagittarii

At 1460 times the radius of our Sun, this supergiant finds itself at the top of the list when it comes to large stars. Located approximately 10000 Light Years away from our Sun, towards the Sagittarius constellation, this red supergiant is otherwise not so known by astronomers.


  1. Ky Cygni

Another red supergiant star belonging to the M spectral class, this star is located in the Cygnus constellation about 5000 Light Years away from Earth. Astronomers describe this star as having about 300000 times the Sun’s luminosity. What is curious about this star is that there are contradicting radiuses that have been measured: the lowest estimate, 1420 times the radius of our Sun consists with similar stars and with theoretical models; the upper estimate, 2850 times the Sun’s radius is thought to be an artifact due to a reddening correction error.


  1. Westerlund 1

This star cluster in the Milky Way is considered to be the most massive young one to be found in the Local Group of galaxies (this group includes 54 galaxies, including the Milky Way, the Andromeda, the Triangulum, Canis Major Dwarf and many more ). Although it was discovered in the 1960s it remained unstudied because of the high interstellar absorption in its direction, but has now been shown to contain 6 yellow hypergiants, 4 red supergiants, 24 Wolf Rayet stars (evolved, massive stars that are rapidly losing mass due to strong stellar winds) and many OB supergiants.


  1. VY Canis Majoris

As the name would have it, this red hypergiant is located in the Canis Major constellation and is one of the most luminous stars of its type. At approximately 1420 times the solar radii, VY Canis Majoris is described as a single, semiregular variable with an estimated period of 2000 days. To picture its size, if it were placed at the center of our Solar System, it would extend beyond Jupiter’s orbit.


  1. RW Cephei

Located in the Cepheus constellation, this red hypergiant is considered to be 1260-1610 times the solar radii (this discrepancy exists because this star is variable both in brightness and in spectral type).


  1. PZ Cassiopeiae

A red suprgiant consistent with theoretical models, PZ Cassiopeiae is located, as the name suggests, in the Cassiopeia constellation and is one of the extreme luminous stars. Its size is estimated at about 1190-1940 times the solar radii, this great difference due to measurement corrections and it is believed to be at 17800 Light Years from the Earth.


  1. VV Cephei

Also known as HD 208816 is a binary star system located in the Cepheus constellation, 5000 Light years from Earth. The composing stars are VV Cephei A, a red supergiant and a companion blue star to which matter seems to flow from the former. Because it is surrounded by shells of extended atmosphere, the star is not spherical and therefore, measuring its radius is difficult, but it is estimated at around 1050 solar radii.