Lunar ephemeris with topocentric librations
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This page contains a JavaScript program that will generate a monthly lunar
ephemeris for your location. The libration figures and the position angle of the
Moon's rotation axis have been corrected for your position on the earth, so they
are topocentric values. To calculate a monthly ephemeris, just
- fill in the form below
- click the 'make table' button
- a new browser window will appear, and the results will print in this
window after a delay of some seconds
- save or print your results
- close the new window to return to this page
The position routines for the Moon ephemeris are approximate, and I have left
out the nutation, physical libration and light time corrections. Save this web
page to your hard drive if you want to make more calculations.
Key to table
The following quantities are listed in the monthly table.
Date:
The date in the given Month. All quantities below are calculated at 0h zone
time on the date.
LST: Local Siderial Time at 0h zone time on the
date. Compare with the RA of the Moon to see how far Moon is from your Meridian
at 0h zone time.
Ra: The geocentric right ascension of the Moon at 0h
zone time on the current day.
Dec: The geocentric declination of the
Moon at 0h zone time on the current day.
L:
Selenographic
longitude of the sub-Earth point. This number tells you how far round the Moon's
face is turned by the optical libration. This figure is corrected for your
position on the Earth's surface. B: Selenographic longitude of the
sub-Earth point. This figure tells you how much the pole of the Moon appears
tilted towards or away from us by the optical libration. This figure is
corrected for your position on the Earth's surface. PA rot: Position
angle of the Moon's axis of rotation. This figure is corrected for your position
on the Earth's surface. Co: Colongitude of the Sun. Listed in
ephemerides. Bs: Selenographic latitude of Sub-Solar point. Tells you
the latitude of the 'pole' of the bright hemisphere of the Moon. Ls:
Selenographic longitude of Sub-Solar point. Tells you the longitude of the
'pole' of the bright hemisphere of the Moon. L term: Selenographic
longitude of terminator. I personally find this a bit easier to interpret than
the colongitude. Following a suggstion from Ralph Sadler, the letter 'r'
indicates that the sun is rising at the given longitude (waxing Moon), and 's'
indicates that the sun is setting (waning Moon). % Ill Illuminated
percentage of the Moon's disc PA bl: Position angle of the bright
limb. Imagine a line drawn from the centre of the Moon's disc to the part of the
bright limb midway between the cusps or horns of the crescent. The PA Bright
Limb is the angle between this line and the Celestial North Pole.
Use offline
Save this page to your hard drive for use off-line - it will still work.
Explore the program by loading the page into a text editor. My excursion into
Javascript was prompted by an article called 'Scripting: A programming
alternative' by David
Benn in the March 2000 issue of Sky and Telescope. A look at Peter Hayes' code
helped me produce the table as a Web page.
Keith Burnett Original
location: http://www.xylem.demon.co.uk/kepler/topomoon.htm Last
modified: 25 April 2000 |