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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]
The new definitions of Greenwich mean and apparent sidereal time (since 2003, see above) are: (,) = () (,) = () such that θ is the Earth Rotation Angle, E PREC is the accumulated precession, and E 0 is equation of the origins, which represents accumulated precession and nutation. [ 15 ]
As seen from above the Earth's north pole, a star's local hour angle (LHA) for an observer near New York. Also depicted are the star's right ascension and Greenwich hour angle (GHA), the local mean sidereal time (LMST) and Greenwich mean sidereal time (GMST). The symbol ♈︎ identifies the March equinox direction.
According to the definitions of the angles on the celestial sphere GHA = GAST − α (see hour angle) where: GAST is the Greenwich apparent sidereal time (the angle between the apparent vernal equinox and the meridian in the plane of the equator). This is a known function of UT. [29]
Right ascension (blue) and declination (green) as seen from outside the celestial sphere Various hour angles are depicted here. The symbol ♈︎ marks the March equinox direction. Assuming the day of the year is the March equinox: the Sun lies toward the grey arrow, the star marked by a green arrow will appear to rise somewhere in the east ...
When you think about astrology—i.e., when you put your sun, moon, and rising in your Instagram bio, or look up your daily horoscope online—you’re likely thinking about tropical astrology ...
On a prograde planet like the Earth, the sidereal day is shorter than the solar day. At time 1, the Sun and a certain distant star are both overhead. At time 2, the planet has rotated 360° and the distant star is overhead again (1→2 = one sidereal day). But it is not until a little later, at time 3, that the Sun is overhead again (1→3 = one solar day). More simply, 1→2 is a complete ...
Sidereal hour angle is a measurement between 0° and 360°, indicating how far west a body is from an arbitrarily chosen point on the celestial sphere called the First Point of Aries. Note that right ascension, as used by astronomers, is 360° minus the sidereal hour angle.