Solar radius

Measurements

The uncrewed 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 696342 ±.

Haberreiter, Schmutz & Kosovichev (2008) determined the radius corresponding to the solar photosphere to be 695660 ±. This new value is consistent with helioseismic estimates; the same study showed that previous estimates using inflection point methods had been overestimated by approximately 300 km.

Nominal solar radius

In 2015, the International Astronomical Union passed Resolution B3, which defined a set of nominal conversion constants for stellar and planetary astronomy. Resolution B3 defined the nominal solar radius (symbol R^{N}_{\odot}) to be equal to exactly . The nominal value, which is the rounded value, within the 140 km uncertainty band 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 units of distance measurement are common especially when describing the paths of spacecraft moving close to the sun. Two such spacecraft in the 2010s include:

• Solar Orbiter (which flew as close as to the sun)
• Parker Solar Probe (which flew as close as to the sun)

References

References

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