nenupy.astro.astro_tools.radec_to_altaz

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

Converts a celestial object equatorial coordinates to horizontal coordinates.

If fast_compute=True is selected, the computation is accelerated using Local Sidereal Time approximation (see local_sidereal_time()). The altitude \(\theta\) and azimuth \(\varphi\) are computed as follows:

\[\begin{split}\cases{ \sin(\theta) = \sin(\delta) \sin(l) + \cos(\delta) \cos(l) \cos(h)\\ \cos(\varphi) = \frac{\sin(\delta) - \sin(l) \sin(\theta)}{\cos(l)\cos(\varphi)} }\end{split}\]

with \(\delta\) the object’s declination, \(l\) the observer’s latitude and \(h\) the Local Hour Angle (see hour_angle()). If \(\sin(h) \geq 0\), then \(\varphi = 2 \pi - \varphi\). Otherwise, transform_to() is used.

Parameters:

  • radec (SkyCoord) – Celestial object equatorial coordinates.

  • time (Time) – Coordinated universal time.

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

  • fast_compute (bool) – If set to True, it enables faster computation time for the conversion, mainly relying on an approximation of the local sidereal time. All other values would lead to accurate coordinates computation. Differences in coordinates values are of the order of \(10^{-2}\) degrees or less.

Returns:

Celestial object’s horizontal coordinates. If either radec or time are 1D arrays, the resulting object will be of shape (time, positions).

Return type:

SkyCoord

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

altaz = radec_to_altaz(
    radec=SkyCoord([300, 200], [45, 45], unit="deg"),
    time=Time("2022-01-01T12:00:00"),
    fast_compute=True
)