nenupy.astro.astro_tools.hour_angle

nenupy.astro.astro_tools.hour_angle(radec, time, observer=<EarthLocation (4323936.68522791, 165534.49991696, 4670345.36540385) m>, fast_compute=True)[source]

Local Hour Angle of an object in the observer’s sky. It is defined as the angular distance on the celestial sphere measured westward along the celestial equator from the meridian to the hour circle passing through a point.

The local hour angle \(h\) is computed with respect to the local sidereal time \(t_{\rm LST}\) and the astronomical source (defined as radec) right ascension \(\alpha\):

\[h = t_{\rm LST} - \alpha\]

with the rule that if \(h < 0\), a \(2\pi\) angle is added or if \(h > 2\pi\), a \(2\pi\) angle is subtracted.

Parameters:

  • radec (SkyCoord) – Sky coordinates to convert to Local Hour Angles.

  • time (Time) – UTC time a which the hour angle is computed.

  • observer (EarthLocation) – Earth location where the observer is at. Default is NenuFAR’s position.

  • fast_compute (bool) – If set to True, an approximation is made while computing the local sidereal time. Default is True.

Returns:

Local hour angle.

Return type:

Longitude

Example:
from nenupy.astro import hour_angle
from astropy.coordinates import SkyCoord
from astropy.time import Time

ha = hour_angle(
    radec=SkyCoord(300, 45, unit="deg"),
    time=Time("2022-01-01T12:00:00"),
    fast_compute=True
)