Below are lists of the largest stars currently known, ordered by radius and separated into categories by galaxy. The unit of measurement used is the

radius of the Sun Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: :1\,R_ = 6.9 ...

(approximately ). The angular diameters of stars can be measured directly using stellar interferometry. Other methods can use lunar occultations or from eclipsing binaries, which can be used to test indirect methods of finding stellar radii. Only a few useful supergiant stars can be occulted by the Moon, including Antares A (Alpha Scorpii A). Examples of eclipsing binaries are Epsilon Aurigae (Almaaz), VV Cephei, and V766 Centauri (HR 5171). Angular diameter measurements can be inconsistent because the boundary of the very tenuous atmosphere (

opacity Opacity or opaque may refer to: * Impediments to (especially, visible) light: ** Opacities, absorption coefficients ** Opacity (optics), property or degree of blocking the transmission of light * Metaphors derived from literal optics: ** In lingu ...

) differs depending on the wavelength of light in which the

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

is observed. Uncertainties remain with the membership and order of the lists, especially when deriving various parameters used in calculations, such as stellar

luminosity Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...

and

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

. Often stellar radii can only be expressed as an average or be within a large range of values. Values for stellar radii vary significantly in different sources and for different observation methods. All the sizes stated in these lists have inaccuracies and may be disputed. The lists are still a work in progress and parameters are prone to change.

Caveats

Various issues exist in determining accurate radii of the largest stars, which in many cases do display significant errors. The following lists are generally based on various considerations or assumptions; these include: * Stellar radii or diameters are usually derived only approximately using Stefan–Boltzmann law for the deduced stellar

and effective surface temperature. * Stellar distances, and their errors, for most stars, remain uncertain or poorly determined. * Many supergiant stars have extended atmospheres, and many are within opaque dust shells, making their true effective temperatures and surfaces highly uncertain. * Many extended supergiant atmospheres also significantly change in size over time, regularly or irregularly pulsating over several months or years as variable stars. This makes adopted

luminosities Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In astronomy, luminosity is the total amount of electromagnetic energy emitted per unit of time by a st ...

poorly known and may significantly change the quoted radii. * Other direct methods for determining stellar radii rely on lunar occultations or from eclipses in binary systems. This is only possible for a very small number of stars. * Most distance estimates for red supergiants come from stellar cluster or association membership, because it is difficult to calculate accurate distances for red supergiants that are not part of any cluster or association. * In these lists are some examples of extremely distant extragalactic stars, which may have slightly different properties and natures than the currently largest known stars in the Milky Way. For example, some red supergiants in the Magellanic Clouds are suspected to have slightly different limiting temperatures and

. Such stars may exceed accepted limits by undergoing large eruptions or changing their spectral types over just a few months (or potentially years).

Lists

The following lists show the largest known stars based on the host galaxy.

Milky Way

Magellanic Clouds

M31 and M33

Other galaxies (within the Local Group)

Outside the Local Group

Notes

References

External links

Giant Stars
An interactive website comparing the Earth and the Sun to some of the largest known stars
Three largest stars identified
BBC News
What is the Biggest Star in the Universe?
Universe Today {{DEFAULTSORT:Largest stars, List of Hypergiants Supergiants Largest Stars, largest Largest stars