torchsky.coords¶

Rotate or observe (lon, lat) tensors. Returns (lon_out, lat_out).

Geometric frames use CatalogState.to_frame. ALTAZ, ITRS, GCRS, CIRS, and TETE require obstime_mjd_utc and eop. ECLIPTIC_OF_DATE uses TT MJD (obstime_mjd_utc is treated as TT unless you pass a TT value through CatalogState.to_frame).

Parameters:

Returns:

Examples:

>>> import torch
>>> from torchsky.coords import transform
>>> lon, lat = transform(torch.tensor([0.0]), torch.tensor([0.0]), from_frame="ICRS", to_frame="GALACTIC")
>>> lon.shape == lat.shape
True

Convert between the currently supported celestial frames.

Heliocentric radial velocity → LSR (km/s) with explicit solar UVW.

Rotate ICRS to the mean ecliptic of date via IAU 2006 NPB.

tt_mjd is TT MJD. This is a geometric frame, not observed place: no aberration, refraction, or site.

Heliocentric ICRS spherical → Galactocentric Cartesian (kpc).

Origin at the Galactic Centre (galcen_ra_deg / galcen_dec_deg). +x toward the anticenter (Sun at x ≈ -R0), +y in rotation, +z toward the NGP. z_sun_pc tilts the midplane so the Sun sits at z = z_sun. Solar peculiar velocity is not applied.

Propagate angular coordinates with proper motion.

pm_lon_coslat_mas_yr is the conventional longitude proper motion with the cosine-of-latitude factor already applied (for ICRS, pm_ra_cosdec). Epochs are Julian years. Inputs broadcast and outputs are longitude and latitude in degrees, with longitude wrapped to [0, 360).

This follows the same unit-distance Cartesian propagation used by SkyCoord.apply_space_motion when distance and radial velocity are not supplied. It stays well behaved at the poles, unlike dividing a longitude increment by cos(latitude).

Parameters:

Returns:

Examples:

>>> from torchsky.wcs import propagate_proper_motion
>>> lon, lat = propagate_proper_motion(10.0, 20.0, 0.0, 0.0, source_epoch_jyear=2000.0, target_epoch_jyear=2010.0)
>>> round(float(lon), 6), round(float(lat), 6)
(10.0, 20.0)

Propagate a complete barycentric astrometric state in ICRS.

Inputs and outputs are longitude/latitude in degrees, cosine-weighted longitude and latitude proper motions in mas/yr, parallax in mas, and radial velocity in km/s. Epochs are TCB Julian years. Inputs broadcast.

The implementation follows the ERFA/SOFA starpv to rectilinear motion with changing light time to pvstar model, including the special- relativistic conversion between catalogue observables and inertial velocity. A complete state is required: use :func:propagate_proper_motion when distance or radial velocity is unavailable.

Returns:

Parameters:

Examples:

>>> from torchsky.wcs import propagate_space_motion
>>> result = propagate_space_motion(10.0, 20.0, 0.0, 0.0, 10.0, 0.0, source_epoch_jyear=2000.0, target_epoch_jyear=2000.0)
>>> len(result)
6

Apply or remove Differential Chromatic Refraction on (ra_deg, dec_deg).

Shift sky coordinates into (or out of) a moving target's comoving frame.

Parameters¶

tracking_rate (dra_cosdec_arcsec_per_hr, ddec_arcsec_per_hr) non-sidereal rate. inverse If False (default), maps sidereal sky coordinates at mjd_obs into the comoving target frame at reference_mjd (subtracting target motion). If True, maps comoving coordinates back to sidereal coordinates at mjd_obs.

Apply atmospheric refraction to altitude in degrees.

Classical stellar aberration: normalize(p + v/c).

Compute Differential Chromatic Refraction (DCR) tangent-plane offset (d_east_deg, d_north_deg).

Returns the apparent chromatic shift toward zenith at wavelength_angstrom relative to ref_wavelength_angstrom in degrees along local East and North.

Return (az_deg, alt_deg) from north toward east.

obstime_mjd_utc is UTC MJD. UT1 = UTC + DUT1. Polar motion is applied when xp/yp are set.

pn=None (default) and pn='iau2006' apply Fukushima-Williams bias-precession and IAU 2000A nutation via the CIRS matrix; with aberration=True this matches astropy AltAz to about 1 arcsec. TT−UTC is eop.tt_minus_utc_s when set, otherwise 32.184 s + TAI−UTC from torchsky's leap-second table; an epoch outside that table (before 1972, or after its expiry) raises ValueError rather than guessing. pn='none' is an explicit opt-in that omits precession-nutation and uses GMST; it is approximate (~0.3 deg off) and is continuous in xp/yp (zero polar motion equals no polar motion). aberration=True converts the astrometric ICRS direction to the apparent place as ERFA atciq does: solar light deflection plus annual and diurnal aberration (the observer's Earth-rotation velocity), with the epv00 Earth ephemeris. Without refraction the result agrees with erfa.atco13 to < 1 mas (residual: TIO locator s' = 0, observer offset in the solar deflection, TT used for TDB). refraction=True applies the ERFA refco model (A tan z + B tan^3 z, honouring site.relative_humidity and site.wavelength_um) to the topocentric direction as atioq does; refraction_model="saemundsson" selects the Saemundsson/Meeus altitude formula instead. Both are off unless requested and need site.pressure_mbar and site.temperature_c.

Time-only quantities are evaluated in float64 on CPU on every device; only the final rotation matrices move to the coordinate device (CUDA float64, MPS float32). Gradients flow through the coordinates. The kernels are ATen, not fused C++.