[AstroPy] Coords v0.3 release now available
Victoria G. Laidler
Mon Feb 12 14:27:39 CST 2007
Version 0.3 of the Coords package has been released and is now available
at http://stsdas.stsci.edu/astrolib . This release expands support for
in AstroDate and Position.
The following changes have been made:
- timetag specification is now supported for TPM-related methods of
Position objects. (See "An explanatory note about time", below,
for more discussion.)
- the AstroDate factory function was enhanced to accept a
datetime.datetime object (assumed to be in UTC) as a time
specification, and to produce a JulianDate of "utc now" when no
argument is supplied.
- tests were refactored; coords._test() now runs a doctest that
matches the set of (now expanded) examples given to demonstrate
package functionality. Unit tests were removed from the
distribution and documentation. The package import statements were
also trimmed down to avoid unnecessarily cluttering the namespace.
An explanatory note about time:
There are three times of interest associated with a celestial
coordinate. TPM calls these
- the equinox == time at which precession is zero
- the epoch == time at which proper motion is zero
- the timetag of the coordinate
The Coords package enforces the following conventions:
equinox=B1950 for galactic coordinates and J1984 for ecliptic
coordinates may be specified at J2000 or B1950, or at an arbitary
Julian (decimal) year.
epoch=J2000 is enforced for all coordinate systems
timetag="time now" (current system time) by default for all coordinate
an arbitrary timetag may be specified as an AstroDate.
Galactic and celestial coordinate systems are very insensitive to
changes in "time now", but due to the nature of the ecliptic reference
frame, ecliptic coordinates are quite sensitive.
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