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Hour angle

Astronomy  Hotspots  Hour circle

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

Hour Angle The angle, measured westwards around the celestial equator, between the observer's meridian and the hour circle of an object.
Hour Circle (i) A great circle passing through an object and the celestial poles. (ii) The setting circle on the polar axis of an equatorial mount.
I ...


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 ...

Local ~ - The angle, measured westward around the celestial equator, between the meridian and the point on the equator nearest a particular celestial object
Long-period Comet - A comet with an orbital period of 200 years or longer ...

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

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

the ~ system is fixed to the Earth like the geographic coordinate system
the right ascension system is fixed to the stars, thus, during a night or a few nights, it appears to move across the sky as the Earth spins and orbits under the fixed stars.

HA; ~ ((astronomy) the angular distance of a celestial point measured westward along the celestial equator from the zenith crossing; the right ascension for an observer at a particular location and time of day) ...

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

~ Angular distance west of a celestial meridian or hour circle; the arc of the celestial equator, or the angle at the celestial pole, between the upper branch of a celestial meridian or hour circle and the hour circle of a celestial body or the vernal equinox, ...

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The next concept we want to define is that of an ~. 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 geographic poles of the earth).

This method works even with the oldest-style setting circles that only read ~ from the celestial meridian instead of right ascension. (These are identified by their 0 to 12 hour markings that can't be set to anything but 0 when the scope is pointed at the meridian.) ...

2.04 The point directly overhead an observer is the...

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 ~ then more sunlight would reflect back and it would appear brighter.

See also: See also: What is the meaning of Earth, Orbit, Astro, Sun, Solar?

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