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Basic astronomical calculations (:mod:`pwkit.astutil`)

.. automodule:: pwkit.astutil
   :synopsis: basic astronomical utilities


.. currentmodule:: pwkit.astutil

This topics covered in this module are:

Angles are always measured in radians, whereas some other astronomical codebases prefer degrees.

Useful Constants

The following useful constants are provided:

pi
Mathematical π.
twopi
Mathematical 2π.
halfpi
Mathematical π/2.
R2A

A constant for converting radians to arcseconds by multiplication:

arcsec = radians * astutil.R2A

Equal to 3600 * 180 / pi or about 206265.

A2R

A constant for converting arcseconds to radians by multiplication:

radians = arcsec * astutil.A2R
R2D
Analogous to R2A: a constant for converting radians to degrees
D2R
Analogous to A2R: a constant for converting degrees to radians
R2H
Analogous to R2A: a constant for converting radians to hours
H2R
Analogous to A2R: a constant for converting hours to radians
F2S

A constant for converting a Gaussian FWHM (full width at half maximum) to a standard deviation (σ) value by multiplication:

sigma = fwhm * astutil.F2S

Equal to (8 * ln(2))**-0.5 or about 0.425.

S2F
A constant for converting a Gaussian standard deviation (σ) value to a FWHM (full width at half maximum) by multiplication.
J2000
The astronomical J2000.0 epoch as a MJD (modified Julian Date). Precisely equal to 51544.5.

Sexagesimal Notation

.. autosummary::
   fmthours
   fmtdeglon
   fmtdeglat
   fmtradec
   parsehours
   parsedeglat
   parsedeglon


.. autofunction:: fmthours

.. autofunction:: fmtdeglon

.. autofunction:: fmtdeglat

.. autofunction:: fmtradec

.. autofunction:: parsehours

.. autofunction:: parsedeglat

.. autofunction:: parsedeglon

Working with Angles

.. autosummary::
   angcen
   orientcen
   sphdist
   sphbear
   sphofs
   parang


.. function:: angcen(a)

   “Center” an angle *a* to be between -π and +π.

   This is done by adding or subtracting multiples of 2π as necessary. Both
   *a* and the return value are in radians. The argument may be a vector.


.. function:: orientcen(a)

   “Center” an orientation *a* to be between -π/2 and +π/2.

   This is done by adding or subtract multiples of π as necessary. Both *a*
   and the return value are in radians. The argument may be a vector.

   An “orientation” is different than an angle because values that differ by
   just π, not 2π, are considered equivalent. Orientations can come up in the
   discussion of linear polarization, for example.


.. autofunction:: sphdist

.. autofunction:: sphbear

.. autofunction:: sphofs

.. autofunction:: parang

Simple Operations on 2D Gaussians

.. autofunction:: gaussian_convolve

.. autofunction:: gaussian_deconvolve

Basic Astrometry

The :class:`AstrometryInfo` class can be used to perform basic astrometric calculations that are nonetheless fairly accurate.

.. autoclass:: AstrometryInfo

   The attributes encoding the astrometric data are as follows. Values of
   ``None`` will be treated as unknown. Most of this information can be
   automatically filled in from the :meth:`fill_from_simbad` function, if you
   trust Simbad.

   .. autosummary::
      ra
      dec
      pos_u_maj
      pos_u_min
      pos_u_pa
      pos_epoch
      promo_ra
      promo_dec
      promo_u_maj
      promo_u_min
      promo_u_pa
      parallax
      u_parallax
      vradial
      u_vradial

   Methods are:

   .. autosummary::
      verify
      predict
      print_prediction
      predict_without_uncertainties
      fill_from_simbad
      fill_from_allwise

   The stringification of an :class:`AstrometryInfo` class formats its fields
   in a human-readable, multiline format that uses Unicode characters.


.. autoattribute:: AstrometryInfo.ra

.. autoattribute:: AstrometryInfo.dec

.. autoattribute:: AstrometryInfo.pos_u_maj

.. autoattribute:: AstrometryInfo.pos_u_min

.. autoattribute:: AstrometryInfo.pos_u_pa

.. autoattribute:: AstrometryInfo.pos_epoch

.. autoattribute:: AstrometryInfo.promo_ra

.. autoattribute:: AstrometryInfo.promo_dec

.. autoattribute:: AstrometryInfo.promo_u_maj

.. autoattribute:: AstrometryInfo.promo_u_min

.. autoattribute:: AstrometryInfo.promo_u_pa

.. autoattribute:: AstrometryInfo.parallax

.. autoattribute:: AstrometryInfo.u_parallax

.. autoattribute:: AstrometryInfo.vradial

.. autoattribute:: AstrometryInfo.u_vradial

.. automethod:: AstrometryInfo.verify

.. automethod:: AstrometryInfo.predict

.. automethod:: AstrometryInfo.print_prediction

.. automethod:: AstrometryInfo.predict_without_uncertainties

.. automethod:: AstrometryInfo.fill_from_simbad

.. automethod:: AstrometryInfo.fill_from_allwise

A few helper functions may also be of interest:

.. autosummary::
   load_skyfield_data
   get_2mass_epoch
   get_simbad_astrometry_info


.. autofunction:: load_skyfield_data

.. autofunction:: get_2mass_epoch

.. autofunction:: get_simbad_astrometry_info

Miscellaneous Astronomical Computations

These functions don’t fit under the other rubrics very well.

.. autosummary::
   abs2app
   app2abs


.. autofunction:: abs2app

.. autofunction:: app2abs