Some day ago Anselmo Perez Serrada has given a simple and precise formula
for the calculation of the sideral time at the first meridian (Longitude =
0°):
ST(at First Meridian) = UT + 2*NrMonth + 4.5
where NrMonth 1.00 for Jan 1st, 1.50 for Jan 15ht, 3.25 for March 8th
If we want the Local Sideral Time, that tells us from how many hours the
Vernal Point is passed at our meridian and what is the Right Ascension of a
star that is at the meridian itself, we may use the following formula, that
derives from that of Anselmo:
Local ST = Time_of_the_clock + TZ - Longitude/15 + 2*NrMonth + 4.64
hours
The value 4.64 instead of 4.5 from a better precision.
The TZ and the Longitude ar positive if West.
With some calculations I have found that in the days of the years from 2000
at 2003 (1461 days) the maximum error that we have (Value_from_formula -
True_Value) is always between +5m and -8m.
If we know the Local Apparenty Time ( the time of a sundial) we have :
Local ST = Apparent_Local_Time + TEq_min/60 + 2*NrMonth + 4.64 hours
These formulas can be useful, for instance, to draw on a sundial the lines
with constant Sideral Time or the line that shaws on the dial when a star
or a constellation will pass at the meridian.
For example : the line that tells us that in 12 hours the Vernal point
will pass at the meridian or that tells that in 8 hours we will have at
South the constellation of Scorpio; etc.
Best regards
Gianni Ferrari
44° 39' N 10° 55' E
Mailto : [EMAIL PROTECTED]
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