Lunar Perigee and Apogee Calculator
To display the date, time, and distance of lunar perigees and apogees
for a given year, enter the year in the box below and press
"Calculate". Depending on the speed of your computer, it may
take a while for the results to appear in the text boxes. This
page requires your browser to support JavaScript, and that JavaScript
be enabled; all computation is done on your own computer so you can,
if you wish, save this page in a file and use
it even when not connected to the Internet.
All dates and times are Universal time (UTC); to convert to local time
add or subtract the difference between your time zone and UTC,
remembering to include any additional offset due to summer time for
dates when it is in effect. For each perigee and apogee
the distance in kilometres between the centres of the Earth
and Moon is given. Perigee and apogee distances are usually accurate
to within a few kilometres compared to values calculated with the
definitive ELP 2000-82 theory of the lunar orbit; the maximum error
over the years 1977 through 2022 is 12 km in perigee distance and
6 km at apogee.
The closest perigee and most distant apogee of the year are marked
with "++" if closer in time to full Moon or "--" if
closer to new Moon. Other close-to-maximum apogees and perigees are
flagged with a single character, again indicating the nearer phase.
Following the flags is the interval between the moment of perigee or
apogee and the closest new or full phase; extrema cluster on the
shorter intervals, with a smaller bias toward months surrounding the
Earth's perihelion in early January. "F" indicates the perigee or
apogee is closer to full Moon, and "N" that new Moon is closer. The
sign indicates whether the perigee or apogee is before ("-") or after
("+") the indicated phase, followed by the interval in days and hours.
Scan for plus signs to find "photo opportunities" where the Moon is
full close to apogee and perigee.
This table gives the time of all new and full Moons in the indicated
year, as well as the last phase of the preceding year and the first
phase of the next year.
References
Click on titles to order books on-line from
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- Meeus, Jean.
Astronomical Algorithms
. Richmond: Willmann-Bell,
1998. ISBN 0-943396-63-8.
- The essential reference for computational positional
astronomy. The calculation of perigee and apogee time and distance
is performed using the algorithm given in Chapter 48.
- Meeus, Jean.
Astronomical Formulæ for Calculators, Fourth Edition
.
Richmond: Willmann-Bell,
1988. ISBN 0-943396-22-0.
- This book, largely superseded by the more precise algorithms
given in Astronomical Algorithms, remains valuable when
program size and speed are more important than extreme precision.
The date and time of the phases of the Moon are calculated using
the method given in Chapter 32, and are accurate within 2 minutes,
more than adequate for our purposes here. The more elaborate
method in Chapter 47 of Astronomical Algorithms
reduces the maximum error to 17.4 seconds (and mean error to
less than 4 seconds), but would substantially increase the size
and download time for this page, and the calculation time for
each update.
- Chapront-Touzé, Michelle and Jean Chapront.
Lunar Tables and Programs from 4000 B.C. to A.D. 8000
.
Richmond: Willmann-Bell, 1991. ISBN 0-943396-33-6.
- If you need more precise calculation of the Moon's position than
given in the references above, you're probably going to end up
here. This book presents the ELP 2000-85 theory which, while
less accurate than ELP 2000-82, has been tested for stability over
a much longer time span. ELP 2000-85 generates predictions of
lunar longitude accurate to 0.0004 degrees for the years 1900
through 2100, and 0.0054 degrees for the period 1500 through 2500.
- Chapront-Touzé, Michelle and Jean Chapront.
Lunar solution ELP 2000-82B.
- This is the most precise semi-analytical theory of the Moon's
motion for observations near the present epoch. Machine-readable
files for all of the tables and a sample FORTRAN program which
uses them to compute lunar ephemerides may be obtained from the
Astronomical Data Center
at the NASA Goddard
Space Flight Center by FTP across the Internet, or on
CD-ROM, along with a wide variety of other astronomical
catalogues and tables. This material is intended for
experts in positional astronomy and computation. If you can't
figure it out, don't ask me for help.
by John Walker
May 5, 1997
This document is in the public domain.