heliographic-longitude | space-encyclopedia

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22, May, 2012

Space exploration began with the launch of Sputnik and Astrophysics was born as the application of physics to the phenomena observed by Astronomy, which etymologically means laws of the stars.

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Term	Definition
Heliographic Longitude	Longitude measured for points on the Sun. There is no fixed zero point on the Sun so heliographic longitude is measured from a nominal reference great circle: the solar meridian that passed through the ascending node of the solar equator on the ecliptic on 1 January 1854 at 12.00 UT. Relative to this, longitude is calculated by assuming a uniform sidereal rotation rate of 25.38 days. Tables published in observing handbooks are used by solar observers to determine the position of the solar reference meridian for a given date and time.

Term

Definition

Heliographic Longitude

Longitude measured for points on the Sun. There is no fixed zero point on the Sun so heliographic longitude is measured from a nominal reference great circle: the solar meridian that passed through the ascending node of the solar equator on the ecliptic on 1 January 1854 at 12.00 UT. Relative to this, longitude is calculated by assuming a uniform sidereal rotation rate of 25.38 days. Tables published in observing handbooks are used by solar observers to determine the position of the solar reference meridian for a given date and time.