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What Is the Sun's Luminosity Class?

While the sun is unique in terms of its impact on the Earth and the solar system, in terms of the overall universe, it is a star of average properties. Two of these properties help astronomers to classify all stars. The first is a star's surface temperature, and the second is the star's luminosity. The sun is classified as a class G2V star. The G2 refers to the sun's surface temperature classification, while the V refers to its luminosity classification.

Solar Measuring Stick
- The sun serves as the astrological measuring stic, by which astronomers compare other stars in the universe. Based on the properties of the sun, astronomers have defined key units of measure. For example, one solar mass equals the mass of the sun. Likewise, solar luminosity equals the luminosity of the sun. All the systems for classifying stars are based around these solar units.
Temperature Classification
- The primary system for categorizing main sequence stars, such as the sun, is the Harvard classification. Devised in 1910, this system classifies main sequence stars according to their surface temperate, determined by their spectral composition. The surface temperatures of stars range from 2,000 to 40,000 Kelvin. The Harvard system divides this into seven classes. From hottest to coldest, these classes are assigned the letters O, B, A, F, G, K and M. Each of these is divided into 10 subclasses, numbered from zero to nine.
Luminosity Classification
- In 1943, astronomers devised the Morgan-Keenan, or MK, classification system. This system uses the Harvard system of letters and number, but adds another variable. This additional property represents the luminosity of a star. This luminosity equals the total amount of energy radiated by the star each second. There are five classes of luminosity, represented by roman numerals I through V. The V class is comprised of main sequence stars.
Classification of the Sun
- According to these systems of star classification, the sun is a G2V star. A G class star has a surface temperature between 5,200 and 6,000 Kelvin. As a G2 star, the sun falls in the hottest 30 percent of all G class stars. G class stars, such as the sun, appear yellow in color. Stars that fall within the G classification have masses that range between 0.85 and 1.1 solar masses, or the mass of the sun. Stars within the G classification have luminosities that range between 0.66 and 1.5 solar luminosities, or the brightness of the sun. In terms of the luminosity class of the sun, it falls within the V class, representing all main sequence stars.

Astronomy