Project
=======
Make lunar distance tables for a given period. For every date the
tables contain the true geocentric lunar distances to selected bodies
(Sun and suitable set of planets or stars). The bodies are selected
subject to 1: the body (other then the sun) is far enough from the sun
to be visible 'somewhere on earth'; 2: the lunar distance is less than
about 120 deg, and 3: the angular velocity of the moon is greatest
with respect to these bodies, adding to accuracy. Lunar distances are
given for every 3 hours of UT. No tabulation if the moon is too close
to the sun for observation.
Method
======
Items marked $ are quantified below.
For every date, do the following:
1. If date is $too close$ to New Moon, skip this date.
Implementation: This can be done in advance. Using Emacs function
'phases-of-moon', make a table of New Moon instances in UT in or
near the intended range of data. List the dates to skip according
to the rule below. Pass this list to the program. The program
checks every date against this list.
2. Calculate a table of true geocentric lunar positions for every 3
hours UT.
Implementation: Let 'aa' do this. Use 'awk' to extract a table
containing:
hour, decimal RA, decimal Dec.
3. Calculate approx geocentric positions at 12 UT for all
$bright$ bodies $near enough$ to the ecliptic and $far enough$ from
the sun.
Implementation: Let 'aa' calculate the positions for Sun and
Planets. Take star positions from file adapted from 'star.cat' in
the aa directory (ie bogus entries and Dec>60 deleted). Discard
Venus if its RA differs less than 1 hour from the sun; discard
other planets and stars below 3 hours. List for the remaining
bodies their aa-number, decimal RA, decimal Dec.
4. Tabulate the lunar distances to these bodies at 12UT, 15UT,
and the difference in 3 hours. These are approx values only used
for decision of the bodies to include. Discard all entries with
distance > 120deg.
Implementation: For each of the two lunar positions and for each
listed body, evaluate
distance = arccos ( sin Moon.Dec sin S.Dec
+ cos Moon.Dec cos S.Dec cos Delta RA )
Make a list of aa-number, distance at 12 UT, diff. dist., EW; the
last field to indicate of Moon is East or West of body.
5. Select 5 entries: (4+sun if its dist<120 or 5 ex sun) with largest
differences from the table. Check that we have at least one
easterly and one westerly distance.
Implementation: If the Sun is still listed, select it. Sort the
remaining entries in the distance list on the
diff.dist. field. Select the first entry marked E and the first
entry marked W. Complete selection to 5 bodies from the top of
the list.
6. For these bodies, calculate the exact lunar distances for the
hours (00, 03, 06, 09, 12, 15, 18, 21, 24). Also calculate the
prop.logs (we need the 24UT calculation for the last prop.log).
Implementation: For each body in the selection, do the
following:
-if the body is a star, let 'aa' and 'awk' get the true
(precessed etc) coordinates for 12UT. Calculate the lunar
distances using the stored table of lunar positions and the
distance formula mentioned above.
-for Sun or Planet, let 'aa' and 'awk' calculate a full set of
coordinates for each of the 9 specified times. Proceed as above.
-calculate the prop.log = log 10800 - log |dist(t) - dist(t+3)|
for t=0(3)21.
-store results in format time, distance, prop.log.
7. Format the table of lunar distances and prop.logs in LaTeX.
date | Body1 PL | Body2 PL | ...
---------------------------------------------------
00UT | | |
03 | | |
06 | | |
09 | | |
12 | | |
... | | |
21 | | |
----------------------------------------------------
date | Body1 PL | Body2 PL | ...
---------------------------------------------------
00UT | | |
03 | | |
06 | | |
09 | | |
12 | | |
...
Quantification
==============
Too close to New Moon
reference: http://www.chowk.com/bin/showa.cgi?kshaukat_sep2397
The moon will not be seen unless at least 10-12 deg from the sun at
sunset/sunrise. Quite arbitrarily, we'll omit tabulation if the
New Moon occurs within 24 hours from 12UT of the date in
question. Thus, skip the date of New Moon and if NM occurs before
12 UT, skip the previous date; else skip the next date.
Bright bodies
Selected Stars, Venus, Mars, Jupiter, Saturnus
Near the ecliptic
Keep it simple: |Dec| < 60. Then, we might aswell take just all
Selected Stars.
Far from the Sun
Either RA differs more than 3 hours (Venus:1 hour) or Dec differs
more than 45 deg. But if Dec differs so much, the star is too far
from the ecliptic anyway. This is an intuitive guess.