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 Observers
Calendars
The astronomical calendars presented here were generated
using a program called skycalendar written by John Thorstensen of Dartmouth
College. The C language source code, which can generate a calendar for
any site, is available by from iraf.noao.edu in the contrib
directory.
The times of sunset, the end and beginning of astronomical
twilight, and sunrise are given in local time, including daylight savings,
if in effect. The rising and setting times take into account atmospheric
refraction, the mean semidiameter of the Sun. If the moon rises or sets
during the night, the rising or setting time is printed; around new moon,
the tabulated rising occurs after the tabulated setting, even though the
rising time is always printed first. The zenith distance used for moonrise
and moonset is the same for sunrise and sunset. The last two columns give
the topocentric celestial coordinates for midnight Eastern time.
Since these tabular data have a wide page format they
may be easier to view on a full-screen-wide viewer page.
Here's more about the program that generated the tables,
from the author:
This calendar is designed to provide information useful
for the planning of nighttime observations. The format should minimize
confusion; each line gives the phenomena for a single (local!) night,
and each line is labeled with both evening and morning (local) day and
date. Note that all times given are LOCAL CIVIL (zone) times. DAYLIGHT
SAVINGS time is used from the first Sunday in April to last in October;
this is the present(1986+) convention in the U.S.A.
The rise/set times printed are the times at which the
center of the object is 50 arcminutes below the geometrical horizon.
At the given twilight, the center of the sun is -2.0 degrees below the
geometrical horizon.
The moon positions (and rise/set times) are generated
by an implementation of the Low-Precision formulae in the Astronomical
Almanac. The Almanac states that the error seldom exceeds 0.3 degrees.
Topocentric corrections are included. Comparisons with tables for Kitt
Peak in the NOAO Newsletter indicate that the rise-set times are good
to +- 2 min or so. The moon's RA, Dec, and illuminated fraction are
given for local midnight, regardless of whether the moon is actually
up at that time. Note that the moonrise and moonset times are not printed
if they occur near mid-day.
The LST at evening and morning twilight are tabulated.
This gives an accurate idea of the range of RA's accessible during the
night.
The JD is given (severely rounded off) for local midnight.
Again, this avoids any ambiguity.
Some credits: The sidereal time and Julian date routines
were originally coded in PL/I by Steve Maker of Dartmouth College. The
algorithms originated in the old American Ephemeris. The routine to
convert JD back to calendar date is adapted from Numerical Recipes in
C, by Press et al.
CAUTIONS: I believe that the program which generates
these tables is reasonably accurate. However, it has not been exhaustively
tested, so you should be sure to run 'sanity checks' on the results.
Also, in view of the approximations used, the results should not be
used when high precision is needed. Extension to dates far from the
present (1990) should be done with great caution. The code has not been
tested for the eastern or southern hemishpheres. Rise/set times are
slightly incaccurate and rather confusing at circumpolar latitudes,
where the concept of a 'night' is blurry.
The daylight savings time conventions (if used) are
quite specific (to U. S., post-1986) and subject to change.
I know that the code has many infelicities; if you should find actual
errors,please notify
John.Thorstensen@dartmouth.edu
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