Re: [guide-user] How to put coordinates of the current season instead of J2000.

Bill Gray Nov 22, 2014

> I would use the guide 9.0 with the coordinates of the current 2014
> season marrow instead of the J2000 coordinates.
> How can you do?

For this, you should select Settings... Formats. Here, the 'Epoch'
can be J2000, or B1950, or mean coordinates of date, or apparent
coordinates of date. (Or you can select "other", and choose epochs
such as B1875. These are mostly of historical interest.)

In your case, you will probably want either "apparent coordinates
of date" or "mean coordinates of date". Mean coordinates reflect the
earth's precession. Apparent coordinates add in the effects of
nutation and the aberration of light as the earth goes around the sun.

Mean and apparent coordinates can differ by about half an arcminute.
The difference is sometimes quite reasonably neglected. (For example,
in pointing a telescope, where getting an accuracy of 30" would be
quite good.)

-- Bill