A Triune Boon From the Moon
Wednesday night will be one of the few times in the last 150 years that the moon will appear bigger and fuller and will be easily visible for a longer period, in a cosmic rarity that is expected to occupy thousands of astronomers and sky watchers.
Wednesday’s event results from the coincidence of three astronomical phenomena: The moon will be at its perigee, the point in its orbit where it comes closest to the Earth; this will occur on the night of a full moon; and it will happen on the winter solstice, the longest night of the year.
There is some debate over the last time all three events occurred so close together--within 12 hours--with some sky watchers saying it was in 1866. But other astronomers say it has been at least 150 years, if not more. There have only been a few days over the last 150 years when the moon has appeared closer, and therefore brighter, than it will this week.
On average, the moon orbits 230,640 miles from the Earth’s surface; on Wednesday it will be 221,614 miles away, which will also make for unusually high tides.
Because the moon is so close to the Earth, most experts say that it will appear 14% larger than normal and 7% brighter, and that if the sky is clear, it will offer a detailed look at the moon’s surface even without a telescope.
Using different calculations, other astronomers, including Roger Sinnott, an editor at Sky & Telescope magazine, say the moon might not appear as large as the 14% estimate, but could be 25% brighter than normal.
Whatever the astronomical calculations may be, moon watchers should prepare for a show. The moon will rise at 5:08 p.m. and, as usual, will appear larger when it is closer to the horizon.
Officials at the Rancho Mission Viejo Land Conservancy are publicizing the event by noting that when the same thing occurred in 1866, the Lakota Sioux staged a devastating ambush of soldiers who were guarding a road that led to gold mines in Montana.
According to the Old Farmer’s Almanac, the brightness of the night might have spurred the attack. In any case, the conservancy expects dozens of amateur astronomers to watch the event from its grounds.
Some astronomers, however, caution against unrealistic expectations.
“To the untrained eye, the differences will be relatively subtle. I’m worried people might be disappointed,” said Patrick So, who lectures at Griffith Observatory in Los Angeles. The observatory is not planning a special event, but expects more sky watchers than usual.
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Moonlight Maximized
This year, a full moon, the lunar perigee and the winter solstice--which occurs at 11:44 p.m. tonight--fall in the same 12-hour period for the first time in at least 133 years. Wednesday the full moon is expected to appear larger and brighter than it does without this triple cosmic coincidence.
Sources: Bob Gill, Cal State Fullerton astronomy professor; John Mosley, astronomer, Griffith Observatory; Academic American Encyclopedia; USA TODAY Weather Book; World Book Encyclopedia
