NavList:

   

Reply

A diagnosis is difficult since Sean has not given his results. However,
one frequent point of confusion is the exact meaning of the right
ascension proper motion: seconds of arc vs. seconds of time, seconds per
Julian century vs. milliseconds per Julian year, etc.

Another issue is coordinate rate vs. great circle rate. In other words,
does the unit of RA proper motion get smaller as you approach the poles,
or is it always the same size as the declination unit?

The latter is the modern tendency. Typically, both proper motions are
given in mas (milli arc seconds) per Julian year (exactly 365.25 days).
In other words, they are both in great circle units.

For navigational stars the most reliable catalog is probably the
re-reduction of the Hipparcos satellite observations (van Leeuwen,
2007). That seems to be the default catalog used by SIMBAD.

SIMBAD right ascension proper motions are in great circle units: mas per
Julian year. A note to that effect appears if you hover the mouse
pointer over the place.


http://simbad.u-strasbg.fr/simbad/sim-id?Ident=polaris&NbIdent=1&Radius=2&Radius.unit=arcmin&submit=submit+id

If you demand a high degree of accuracy it's not easy to validate your
own software. You can't be sure how far to trust other applications
until they have been tested. One good test is the stellar reduction
example in every edition of the Astronomical Almanac. It's challenging
since the fictitious star is close and has high proper motion. If your
software succeeds here (within its intended accuracy, not necessarily
matching the Almanac to the last digit), it's almost certainly OK.

https://archive.org/details/binder1_202003/page/n189/mode/2up

The Almanac example stops at the geocentric coordinates. For a reduction
all the way to azimuth and altitude, see the Patrick Wallace example.
It's rather intimidating, but if there's anything weak in your code this
will reveal it.

https://syrte.obspm.fr/iauWGnfa/ExPW04.html

For a detailed discussion on these matters use the "contact me" link at
my site.

--
Paul Hirose
http://sofajpl.com/

   

Reply