astrotool.coordinates module

Coordinate transformations and related functions for AstroTool.

astrotool.coordinates.ecl2eq(lon, lat, eps)

Convert (geocentric) spherical ecliptical coordinates to spherical equatorial coordinates.

Parameters:

• lon (float) – Ecliptical longitude (rad).

• lat (float) – Ecliptical latitude (rad).

• eps (float) – Obliquity of the ecliptic (rad).

Returns:

tuple containing (ra, dec):

• ra (float): Right ascension (rad).

• dec (float): Declination (rad).

Return type:

tuple (float,float)

References

• Explanatory Supplement to the Astronomical Almanac 3rd Ed, Eq.14.43

astrotool.coordinates.eq2ecl(ra, dec, eps)

Convert equatorial coordinates to ecliptical.

Parameters:

• ra (float) – Right ascension (rad).

• dec (float) – Declination (rad).

• eps (float) – Obliquity of the ecliptic (rad).

Returns:

tuple containing (lon, lat):

• lon (float): Ecliptical longitude (rad).

• lat (float): Ecliptical latitude (rad).

Return type:

tuple (float,float)

astrotool.coordinates.geoc2topoc_ecl(lon_gc, lat_gc, dist_gc, rad_gc, eps, lst, lat_obs, ele_obs=0, debug=False)

Convert spherical ecliptical coordinates from the geocentric to the topocentric system.

Parameters:

• lon_gc (float) – Geocentric ecliptic longitude (rad).

• lat_gc (float) – Geocentric ecliptic latitude (rad).

• dist_gc (float) – Geocentric distance (AU).

• rad_gc (float) – Geocentric semi-diameter (rad).

• eps (float) – Obliquity of the ecliptic (rad).

• lst (float) – Local sidereal time (rad).

• lat_obs (float) – Geographical latitude of the observer (rad).

• ele_obs (float) – Altitude/elevation of the observer above sea level (metres, optional, default value = 0).

• debug (bool) – Print debug output (True/False, optional, default value = True).

Returns:

tuple containing (lon_tc, lat_tc, rad_tc):

• lon_tc (float): Topocentric ecliptic longitude (rad).

• lat_tc (float): Topocentric ecliptic latitude (rad).

• rad_tc (float): Topocentric semi-diameter (rad).

Return type:

tuple (float,float,float)

astrotool.coordinates.obliquity(jd)

Compute the obliquity of the ecliptic in radians from the JD(E).

Parameters:

jd (float) – Julian day (days).

Returns:

eps: Obliquity of the ecliptic (rad).

Return type:

float

References

• Seidelman 1992, Eq. 3.222-1.

astrotool.coordinates.par2horiz(ha, dec, phi)

Convert parallactic coordinates to horizontal.

Parameters:

• ha (float) – Hour angle (rad).

• dec (float) – Declination (rad).

• phi (float) – Geographical latitude (rad, N>0).

Returns:

tuple containing (az, alt):

• az (float): Azimuth (rad, S=0).

• alt (float): Altitude (rad).

Return type:

tuple (float,float)

astrotool.coordinates.precess_from_2000(jd, ra, dec)

Compute precession in equatorial coordinates from J2000 to that of the specified JD.

J2000 is the equinox of many catalogues, including the Hipparcos one.

Parameters:

• jd (float) – Julian day (days).

• ra (float) – Right ascension (rad).

• dec (float) – Declination (rad).

Returns:

tuple containing (ra_new, dec_new):

• ra_new (float): Right ascension for the target equinox (rad).

• dec_new (float): Declination for the target equinox (rad).

Return type:

tuple (float,float)

astrotool.coordinates.proper_motion(jd_start, jd_target, ra, dec, pma, pmd)

Compute the proper motion from jd_start to jd_target for the given positions and proper motions.

Parameters:

• jd_start (float) – Julian day of the initial epoch (days).

• jd_target (float) – Julian day of the target epoch (days).

• ra (float) – Right ascension (numpy array, rad).

• dec (float) – Declination (numpy array, rad).

• pma (float) – Proper motion in right ascension (numpy array, rad/yr).

• pmd (float) – Proper motion in declination (numpy array, rad/yr).

Returns:

tuple containing (ra_target, dec_target):

• ra_target (float): Right ascension for the target epoch (rad).

• dec_target (float): Declination for the target epoch (rad).

Return type:

tuple (float,float)