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The Carrington heliographic coordinate system, established by Richard C. Carrington in 1863, rotates with the Sun at a fixed rate based on the observed rotation of low-latitude sunspots. It rotates with a sidereal period of exactly 25.38 days, which corresponds to a mean synodic period of 27.2753 days. [9]: 221 [1] [2] [5]
Solar longitude, commonly abbreviated as Ls, is the ecliptic longitude of the Sun, i.e. the position of the Sun on the celestial sphere along the ecliptic.It is also an effective measure of the position of the Earth (or any other Sun-orbiting body) in its orbit around the Sun, [1] usually taken as zero at the moment of the vernal equinox. [2]
Quadrants are described using ordinals—for example, "1st galactic quadrant", [1] "second galactic quadrant", [2] or "third quadrant of the Galaxy". [3] Viewing from the north galactic pole with 0 degrees (°) as the ray that runs starting from the Sun and through the galactic center, the quadrants are as follows (where l is galactic longitude):
The time when the Sun transits the observer's meridian depends on the geographic longitude. To find the Sun's position for a given location at a given time, one may therefore proceed in three steps as follows: [1] [2] calculate the Sun's position in the ecliptic coordinate system, convert to the equatorial coordinate system, and
The solar azimuth angle is the azimuth (horizontal angle with respect to north) of the Sun's position. [1] [2] [3] This horizontal coordinate defines the Sun's relative direction along the local horizon, whereas the solar zenith angle (or its complementary angle solar elevation) defines the Sun's apparent altitude.
At the equator, the solar rotation period is 24.47 days. This is called the sidereal rotation period, and should not be confused with the synodic rotation period of 26.24 days, which is the time for a fixed feature on the Sun to rotate to the same apparent position as viewed from Earth (the Earth's orbital rotation is in the same direction as the Sun's rotation).
The four quadrants of a Cartesian coordinate system The axes of a two-dimensional Cartesian system divide the plane into four infinite regions , called quadrants , each bounded by two half-axes. The axes themselves are, in general, not part of the respective quadrants.
The geocentric ecliptic system was the principal coordinate system for ancient astronomy and is still useful for computing the apparent motions of the Sun, Moon, and planets. [3] It was used to define the twelve astrological signs of the zodiac , for instance.