Suddenly a
lot of people are asking this question: Will the full Moon of December 22, 1999,
be the brightest full Moon in 133 years?
According to Roger W.
Sinnott, associate editor of Sky & Telescope magazine, the answer
is unequivocal: No!
It is true that there is a most unusual coincidence of events this year. As
S&T contributing editor Fred Schaaf points out in the December 1999 issue of
Sky & Telescope, "The Moon reaches its very closest point
all year on the morning of December 22nd. That's only a few hours after the
December solstice and a few hours before full Moon. Ocean tides will be
exceptionally high and low that day."
But to have these three events -- lunar perigee, solstice, and full Moon --
occur on nearly the same day is not especially rare. The situation was
rather similar in December 1991 and December 1980, as the following dates and
Universal Times show:
| Event |
Dec.
1999 |
Dec.
1991 |
Dec.
1980 |
| Full Moon |
22,
18h |
21,
10h |
21,
18h |
| Perigee |
22,
11h |
22,
9h |
19,
5h |
| Solstice |
22,
8h |
22,
9h |
21,
17h |
So is it really true, as numerous faxes and e-mails to Sky &
Telescope have claimed, that the Moon will be brighter this December 22nd
than at any time in the last 133 years? We have researched the actual perigee
distances of the Moon throughout the years 1800-2100, and here are some perigees
of "record closeness" that also occurred at the time of full Moon:
| Date |
Distance
(km) |
| 1866 Dec. 21 |
357,289 |
| 1893 Dec.
23 |
356,396 |
| 1912 Jan.
4 |
356,375 |
| 1930 Jan.
15 |
356,397 |
| 1999 Dec. 22 |
356,654 |
| 2052 Dec.
6 |
356,421 |
So it turns out that the Moon comes closer to Earth in the years 1893,
1912, 1930, and 2052 than it does in either 1866 or 1999. The difference in
brightness will be exceedingly slight. But if you want to get technical about
it, the full Moon must have been a little brighter in 1893, 1912, and 1930 than
in either 1866 or 1999 (based on the calculated distances).
The 1912 event is undoubtedly the real winner, because it happened on the
very day the Earth was closest to the Sun that year. However, according to a
calculation by Belgian astronomer Jean Meeus, the full Moon on January 4, 1912,
was only 0.24 magnitude (about 25 percent) brighter than an "average"
full Moon.
Our data are from the U.S. Naval Observatory's ICE computer program, Jean Meeus's Astronomical
Algorithms, page 332, and the August 1981 issue of Sky &
Telescope, page 110.