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Zenith stars (also "star on top", "overhead star", "latitude star") [8] are stars whose declination equals the latitude of the observers location, and hence at some time in the day or night pass culminate (pass) through the zenith. When at the zenith the right ascension of the star equals the local sidereal time at your location.
In astronomy, the meridian is the great circle passing through the celestial poles, as well as the zenith and nadir of an observer's location. Consequently, it contains also the north and south points on the horizon, and it is perpendicular to the celestial equator and horizon.
The solar zenith angle is the zenith angle of the sun, i.e., the angle between the sun’s rays and the vertical direction. It is the complement to the solar altitude or solar elevation, which is the altitude angle or elevation angle between the sun’s rays and a horizontal plane.
Zenith, nadir: Altitude (a) or elevation Azimuth (A) North or south point of horizon Equatorial: Center of the Earth (geocentric), or Sun (heliocentric) Celestial equator: Celestial poles: Declination (δ) Right ascension (α) or hour angle (h) March equinox: Ecliptic: Ecliptic: Ecliptic poles: Ecliptic latitude (β) Ecliptic longitude (λ ...
Horizontal coordinates use a celestial sphere centered on the observer. Azimuth is measured eastward from the north point (sometimes from the south point) of the horizon; altitude is the angle above the horizon.
A meridian is the imaginary plane running north–south and through the zenith, nadir, and celestial poles. This is usually done with the equinox Sun at solar noon to determine the observer's latitude, but can be done with any celestial object. Solar noon is the time when the Sun crosses the meridian.
The cosine of the hour angle (cos(h)) is used to calculate the solar zenith angle. At solar noon, h = 0.000 so cos(h) = 1, and before and after solar noon the cos(± h) term = the same value for morning (negative hour angle) or afternoon (positive hour angle), so that the Sun is at the same altitude in the sky at 11:00AM and 1:00PM solar time. [5]
Z is the observer's zenith, or their position on the celestial sphere. X is the position of a celestial body, such as the sun , moon , a planet , or a star . The position of Z or X is described via its declination —the angular distance north or south of the equator (corresponding to its latitude )—and the hour angle —the angle between its ...