nenupy.astro.astro_tools.parallactic_angle

nenupy.astro.astro_tools.parallactic_angle(coordinates, time, observer=<EarthLocation (4323936.68522791, 165534.49991696, 4670345.36540385) m>)[source]

TO DO/Done?

\[q = - {\rm atan2 }( -\sin(h) , \cos(\delta) \tan(l) - \sin(\delta)\cos(h))\]

where \(q\) is the parallactic angle, \(h\) is the hour angle, \(\delta\) is the declination and \(l\) is the observers’s latitude.

Parameters:

  • coordinates (SkyCoord) – Coordinates at which the parallactic angle is evaluated.

  • time (:class:~`astropy.time.Time`) – UT time(s) at which the parallactic angle is evaluated.

  • observer (EarthLocation) – Observer location on the Earth.

Returns:

The parallactic angle.

Return type:

Angle

Example:
from nenupy.astro.astro_tools import parallactic_angle
from nenupy.astro.target import FixedTarget
from astropy.time import TimeDelta

cyga = FixedTarget.from_name('Cyg A')
transit = cyga.next_meridian_transit()
dt = TimeDelta(5*3600, format='sec')
steps = 20
times = transit - dt + np.arange(steps)*(dt*2/steps)
pa = parallactic_angle(
    ra_j2000=cyga.coordinates.ra,
    dec_j2000=cyga.coordinates.dec,
    time=times
)