Fred Koschara

This page is a presentation of John Walker's Lunar Perigee and Apogee Calculator. I do not have or make any claim to or copyright over the material between the horizontal rule following these paragraphs and the page footer, or the Javascript code in the /info/_include or the stylesheet in the /info/_style subdirectories where John has so graciously contributed these materials to the public domain. What I am asserting rights to is my presentation of the page here within my website and the framework used to build it.
I have made some small modifications to fit the page into my site. If you would like to obtain a copy of this page directly from its source, feel free to visit the link above.

Thank you John Walker for contributing this tool for our use!

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.

The Perigee and Apogee Table

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 kilometers between the centers of the Earth and Moon is given. Perigee and apogee distances are usually accurate to within a few kilometers 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.

The Moon Phase Table

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

Meeus, Jean. Astronomical Algorithms . Richmond: Willmann-Bell, 1998. ISBN 978-0-943396-61-3.

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 Formulae for Calculators, Fourth Edition . Richmond: Willmann-Bell, 1988. ISBN 978-0-943396-22-4.

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 978-0-943396-33-0.

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.

Back to Inconstant Moon: Moon at Perigee and Apogee

Return to Earth and Moon Viewer

Other Astronomy and Space resources at fourmilab.ch

This document is in the public domain.