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Re: IDL> How to calculate the position of the Sun?
| Re: IDL> How to calculate the position of the Sun? [message #4014] |
Thu, 20 April 1995 00:00 |
sterner
Messages: 106
Registered: February 1991
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Senior Member |
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Fergus Gallagher <F.Gallagher@nerc.ac.uk> writes:
> I would like to calculate the position of the Sun at a given date & time
> in (geocentric) equatorial coordinates. Anyone got a routine for this?
>
> I have a routine to calculate its RA-Dec but no RA-Dec to lat-long
> coordinate conversion. Must be an astronomer out there with a routine to
> do this......
>
If you mean lat-long on earth (not Celestial Latitude and Longitude)
then it's easy:
lat = dec
lng = 15.0*(ra-st)
Where ra and dec are the sun's Geocentric RA and Dec (which you
already have), and st is the Greenwich Sidereal time.
My IDL library has a routine to compute the sun's position (sun.pro)
and one to compute the local mean sidereal time (lmst.pro).
It also has a routine called sunclock which applies both to give a
world map showing daylight/night/twilights (as I write this the sun
is directly overhead in Trinidad). You can pick up the library as follows:
ftp fermi.jhuapl.edu
login: anonymous
password: your email address
cd pub/idl
get README
bye
The text file README describes what is in the libraries, how to
get them, and how to set them up.
Ray Sterner sterner@tesla.jhuapl.edu
The Johns Hopkins University North latitude 39.16 degrees.
Applied Physics Laboratory West longitude 76.90 degrees.
Laurel, MD 20723-6099
WWW Home page: ftp://fermi.jhuapl.edu/www/s1r/people/res/res.html
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