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Aubrey O'Callaghan wrote:

> I am astro navigation writing some software for my HP49G and have been
> looking for star proper motions for calculation of SHA.
> I have found a good website (http://www.alcyone.de/SIT/SIT_en.htm). However
> I have some questions about the proper motion.
> Looking up the proper motion of Sirius
> (http://www.alcyone.de/SIT/mainstars/SIT000499.htm) get some conflicting
> answers depending upon the source, which should be used to get the Nautical
> almanac equivalent ?

Hi all,

The best source for stellar proper motions nowadays is the Hipparcos
catalogue that is now available at

  http://astro.estec.esa.nl/Hipparcos/hipparcos.html

First, you will need to know the Hipparcos number of your star.

For that, go to

  http://astro.estec.esa.nl/Hipparcos/HIPcatalogueSearch.html

input the approximate J2000 co-ordinates, a tolerance (say 0.1 degree)
and a limiting magnitude (say 4). You will then obtain a short table of
all stars brighter than the limiting magnitude measured near to that
position with precise co-ordinates, magnitudes and proper motion
components with their errors - with a bit of luck there will be just one
star. Click on the star number for more details.

You can also make a plot of your search region with


http://astro.estec.esa.nl/SA-general/Projects/Hipparcos/apps/SelectArea.html

but do not use it when the star is very close to one of the celestial
poles (you will not easily find Polaris in this way).

Note that the proper motion components are given in milli-arcseconds per
year. For correcting the RA co-ordinate, divide the RA proper motion
component by 15 * cos(decl.) to obtain the proper motion in seconds of
time.

In the case of Sirius there is also a 50-year oscillation in RA and
decl. due to the presence of a white dwarf companion (Sirius B).

Regards,

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