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September 2006 Feature: Northernmost Moon of the 21st Century

Moonstruck Many Times Over in September!


Not only does September of 2006 feature the northernmost Moon of the century, but also the closest Full Moon and the farthest New Moon of the year. What's more, a partial lunar eclipse at Full Moon and an annular solar eclipse at new Moon are in the works -- though in North America, as it turns out, we're not in a position to observe either eclipse. The September 7 lunar eclipse is best seen from Asia, Australia, Europe and Africa, and your best bet for observing the September 22 annular solar eclipse is northeastern South America -- in Guyana, Suriname or French Guiana. The above links are maps from Fred Espenak's eclipse page, a treasure chest of eclipse information.
We'll investigate the year's closest Full Moon and farthest New Moon before elaborating upon the northernmost Moon of the century . . .

Closest Full Moon

The Moon looks like it's full for about three days or so, but technically speaking, an astronomical Full Moon represents but a fleeting moment -- the instant the Moon stands most directly opposite the Sun in Earth's sky. This month, the Full Moon comes to pass on September 7, at precisely 6:42 p.m. Universal Time (2:42 p.m. Eastern Daylight Time). At this moment, the Moon is beneath the horizon in North America, and by the time the Moon rises in the east around sunset, it'll be slightly past Full Moon.
For general reference, we can say the Full Moon happens on the night of Sept. 7-8. Moreover, of all the Full Moons this year, this Full Moon aligns most closely with perigee, the Moon's closest approach to the Earth for the month. The February Full Moon, on the other hand, aligned most closely with apogee (the Moon's most distant point from Earth for the month). The September Full Moon, therefore, comes some 30,000 miles closer to Earth than the year's most distant Full Moon in February. For the specific dates and times for New/Full Moons and lunar perigees/apogees, check out this web page, courtesy of John Walker.

Closest Full Moon ushers in Perigean Spring Tide

It is well known that Full (and New) Moons elevate the ocean tides, bringing monthly spring tides. At spring tide, the high tide climbs especially high whereas the low tide falls especially low, so the variation between high and low tide is extreme. But a Full (or New) Moon coinciding with perigee accentuates the spring tide even more, bringing forth what's called a perigean spring tide. If onshore winds and a low barometric pressure prevail as well, flooding along the ocean shorelines is certainly a possibility. Typically, there's a lag time of a few days between Full Moon and the ensuing spring tide, but this Old Farmer's Almanac tide calculator predicts high and low tides for your neck of the woods.
For a lot more information on tides, I invite you to read my February 2006 Feature: Perigean Spring Tide. In February, it was a New Moon perigean spring tide, because it was the month of the year's closest New Moon and farthest Full Moon -- exactly the reverse of September.

Farthest New Moon

The September New Moon comes to pass on September 22, at 11:45 a.m. Universal Time. If you happen to be at the right spot on Earth, you'd see that the Moon and Sun are in perfect alignment. Even so, no total solar eclipse occurs, for the simple reason that the farthest New Moon of the year is too far distant to totally cover over the solar disk. Consequently, you'd see a ring -- or annulus of sunshine -- surrounding the Moon (be sure to use proper eye protection). This is called an annular solar eclipse. The fact that this eclipse happens so close to the day of the equinox (Sept. 23, 4:03 a.m. Universal Time) very much relates to the northernmost Moon phenomenon.

Northernmost Moon!

Northernmost (and southernmost) Moons come in cycles of some 18.5 to 19 years. This year, the northernmost Moon happens on September 15, at 1:27 a.m. Universal Time (Sept. 14, 9:27 p.m. Eastern Daylight Time). The last northernmost Moon fell on Sept. 15, 1987, and the next one will be on March 7, 2025. At the instant of this year's northernmost Moon, the Moon will be at zenith (staight overhead) at India's Thar Desert. In the United States (except for Alaska), the Moon will be underneath the horizon at this time.
Regardless, on September 15 you'll see a Moon that rises and sets considerably farther north, and climbs much higher in the sky, than the Sun ever does on the June solstice. For the rise/set times for the Moon in your area, click here, and for the Moon's rise/transit/set times click here. Northernmost (and southernmost) Moons take place when the Moon is at or near quarter phase, one week before and/or after an eclipse, and within (at most) two weeks of an equinox. For more on the subject, read 2006: Year of Major Lunar Standstill.

Northernmost Moons in the 21st Century*

Date of Northernmost MoonGeocentric** Declination North of Equator
September 15, 200628 degrees 43 minutes 22 seconds
March 7, 202528 degrees 43 minutes 00 seconds
September 25, 204328 degrees 43 minutes 10 seconds
March 18, 206228 degrees 42 minutes 46 seconds
March 18, 208128 degrees 42 minutes 13 seconds
September 8, 209928 degrees 42 minutes 37 seconds
* Source: page 27 of Mathematical Astronomy Morsels by Jean Meeus
** Geocentric means lunar declination is measured from the center of the Earth. For a short discussion on geocentic versus topocentric declination, click here.

copyright 2006 by Bruce McClure

August 2006 Feature * October 2006 Feature


Another September Feature: Lunar Parallax

Eclipse Animations by Shadow & Subtance