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Solar radius is a unit of distance used to express the size of NASA RHESSI oblateness measurements 2012
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The unmanned SOHO spacecraft was used to measure the radius of the Sun by timing transits of Mercury across the surface during 2003 and 2006. The result was a measured radius of .
Haberreiter, Schmutz & Kosovichev (2008) determined the radius corresponding to the solar photosphere to be . This new value is consistent with helioseismic estimates; the same study showed that previous estimates using inflection point methods had been overestimated by approximately .
star
A star is an astronomical object comprising a luminous spheroid of plasma held together by its gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night, but their immense distances from Earth make ...
s in astronomy
Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...
relative to the Sun. The solar radius
In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...
is usually defined as the radius to the layer in the Sun's photosphere
The photosphere is a star's outer shell from which light is radiated.
The term itself is derived from Ancient Greek roots, φῶς, φωτός/''phos, photos'' meaning "light" and σφαῖρα/''sphaira'' meaning "sphere", in reference to it ...
where the optical depth equals 2/3:
:
is approximately 10 times the average radius of Jupiter
Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandt ...
, about 109 times the radius of the Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...
, and 1/215th of an astronomical unit
The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbi ...
, the distance of the Earth from the Sun. It varies slightly from pole to equator due to its rotation, which induces an oblateness in the order of 10 parts per million./ref>
Measurements
The unmanned SOHO spacecraft was used to measure the radius of the Sun by timing transits of Mercury across the surface during 2003 and 2006. The result was a measured radius of .
Haberreiter, Schmutz & Kosovichev (2008) determined the radius corresponding to the solar photosphere to be . This new value is consistent with helioseismic estimates; the same study showed that previous estimates using inflection point methods had been overestimated by approximately .
Nominal solar radius
In 2015, theInternational Astronomical Union
The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach ...
passed Resolution B3, which defined a set of nominal conversion constants for stellar and planetary astronomy
Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...
. Resolution B3 defined the ''nominal solar radius'' (symbol ) to be equal to ''exactly'' . The nominal value, which is the rounded value, within the uncertainty, given by Haberreiter, Schmutz & Kosovichev (2008), was adopted to help astronomers avoid confusion when quoting stellar radii in units of the Sun's radius, even when future observations will likely refine the Sun's actual photospheric radius (which is currently only known to about an accuracy of ±).
Examples
Solar radii as a unit are common when describing spacecraft moving close to the sun. Two spacecraft in the 2010s include: * Solar Orbiter (as close as ) * Parker Solar Probe (as close as )See also
*Astronomical unit
The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbi ...
* List of largest known stars
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 (approximately ).
The angular diameters of stars can be measured directly u ...
* Orders of magnitude (length)
* Solar luminosity
* Solar mass
* Earth Radius
Earth radius (denoted as ''R''🜨 or R_E) is the distance from the center of Earth to a point on or near its surface. Approximating the figure of Earth by an Earth spheroid, the radius ranges from a maximum of nearly (equatorial radius, deno ...
References
External links
* * {{Portal bar, Physics, Astronomy, Stars, Spaceflight, Outer space, Solar System, ScienceRadius
In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...
Stellar astronomy
Units of length