Sun Avoidance
To avoid excessive heating of the feed legs, the prime focus regions, and the cables of the prime focus, the SMT telescope will not be pointed to within 42 degrees of the sun. The following table lists the apparent RA and Dec of the Sun on the first of each month (we have ignored the small year-to-year changes due to precession). Observers are encouraged to use this information to specify their proposal requests for observing time.
| date | ra | dec |
|---|---|---|
| January 1 | 18:43:58 | -23:03:09 |
| February 1 | 20:56:29 | -17:17:11 |
| March 1 | 22:45:56 | -07:50:20 |
| April 1 | 00:39:47 | +04:16:56 |
| May 1 | 02:31:07 | +14:52:24 |
| June 1 | 04:33:49 | +21:57:37 |
| July 1 | 06:38:05 | +23:08:56 |
| August 1 | 08:43:00 | +18:10:52 |
| September 1 | 10:39:07 | +08:31:16 |
| October 1 | 12:27:05 | -02:55:31 |
| November 1 | 14:22:58 | -14:12:38 |
| December 1 | 16:26:20 | -21:41:35 |
Verifying source distance from Sun using Astro:
- Create a temporary catalog, say astro_sun.cat, of the format:
- source b1950_ra b1950_dec "LS" v_lsr
- See example of catalog contents.
- Open program astro by typing "astro" in modelo. smtoast on Mt. Graham.
- Set catalog by typing "catalog astro_sun.cat" (or whatever you've called it)
- Type "horizon /source /planet".
- This will produce a plot showing observability times AND it will list degrees from sun and dates of sun avoidance.
Generating 'Astro' catalogs from ARO catalogs:
The Astro program can read a catalog of objects and can make a plot showing when the objects are up and whether or not they are currently too close to the sun. It will also state the range of dates for which the objects are too close to the sun. The catalog file (default type .sou) is in a different format than used for ARO catalogs (.cat files).
ARO .cat files can be easily converted to .sou files with:
unix_prompt% cat2sou aro.cat > astro_cat.sou
where aro.cat is the ARO catalog file and astro_cat.sou is the resulting Astro format.
The astro_cat is then read into Astro with:
Astro> catalog astro_cat
Set the sun limit to 42 degrees at SMT:
Astro> let sun_limit 42
And a plot can be made with:
Astro> horizon /source
This command also prints out what dates are unsuitable for observing these objects, if any.
A similar plot for planets can be made with
Astro> horizon /planet
Sorry, there's no way to do comets in Astro, other than to get their current RA and Dec and put them in a .cat (or .sou) file as if they were stationary objects.