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Hour angle

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Hour Angle
Related Category: Astronomy: General
in astronomy, a coordinate in the equatorial coordinate system.

Hour Angle
The angle between an observer's and the on which some celestial body lies.

hour angle: [h, HA] the angle corresponding to the sun's position around its daily (apparent) orbit. Measured westward from local noon, it increases at a rate of 15 per hour. Thus 3pm (Local Apparent Time) is 45 and 9 am is -45.

Hour Angle The angle, measured westwards around the celestial equator, between the observer's meridian and the hour circle of an object.


The angle to an object measured westward from the prime meridian (the great circle for a particular observer which goes through the celestial poles and the zenith).

Hour Angle
the telescope based coordinate specifying the angle, in the equatorial plane, from the meridian to a plane containing the celestial object and the north and south celestial poles.
H-R Diagram ...

Hour Angle
Angular distance on the celestial sphere measured westward along the celestial equator from the meridian to the hour circle that passes through a celestial object.
Hour Circle ...

Hour Angle -- The angular distance of a celestial object measured westward along the celestial equator from the zenith crossing. In effect, HA represents the RA for a particular location and time of day.

Hour angle
The sidereal time that has elapsed since the object was on the meridian (hour angle west, positive) or until it will again be on the meridian (hour angle east, negative).

hour angle - (n.)
Of a celestial object as seen from a particular location, the difference between the local sidereal time and the right ascension (H.A. = L.S.T. - R.A.).
H-R diagram - (n.) ...

An hour angle referred to the ephemeris meridian. [S92]
Ephemeris Longitude
Longitude (see Longitude, Terrestrial) measured eastward from the ephemeris meridian. [S92]
Ephemeris Meridian ...

the hour angle system is fixed to the Earth like the geographic coordinate system ...

sidereal hour angle (SHI)
right ascension (RA, ),
Greenwich hour angle (GHA),
local hour angle (LHA) ...

hour angle Angular distance west of a celestial meridian or hour circle; the arc of the celestial equator, or the angle at the celestial pole, ...

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The next concept we want to define is that of an hour angle. For this, we first define the hour circle as a great circle on the celestial sphere that passes through the north and south celestial poles (which are directly above the north and south ...

This method works even with the oldest-style setting circles that only read hour angle from the celestial meridian instead of right ascension.

These deposits will then appear slightly darker than they would if sunlight was directly reflected at the observer. If that same deposit were nearer to the noon hour angle then more sunlight would reflect back and it would appear brighter.

The admittedly informal standard is to have numerals in hot colors for summer, and in cool colors for winter. Twisting the face of the sundial will not work because sundials (except at the north and south pole) do not have equal hour angles.

Star time; the hour angle of the vernal equinox. Time measured with respect to the fixed stars rather than the Sun or body orbiter.
Sidereal Month.
The 27.32166 day period of the Moon's orbit.
Solar Cycle.

See also: See also: Earth, Astro, Sun, Solar, Orbit

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