Four Super-Duper Moons this Month?

Comparison of apparent lunar sizes at perigee and apogee.
Credit: NASA

Checking out the sky is something I do often. Whether it’s passing clouds; aircraft (especially helicopters orbiting low near home); planets and stars; and of course the Moon in any of its phases, such things catch the eye and often evoke speculation.

I experienced some particularly lunar impressiveness one evening last month when what looked like an especially big and bright waxing gibbous Moon was seen just above neighborhood rooftops. That sighting, the night before last month’s “Super Moon” was fortunate because the next evening was cloudy.

August 2014 features the second of three Super Moons this year. The concept has blossomed in public interest during recent years and that’s a good thing—the more folks looking at the night sky the better! 

It’s my understanding the term Super Moon was coined in 1979 by an astrologer, who defined it as an event when a Full or New Moon occurs within 90% of its closest possible approach to Earth—closer than a threshold of about 224,851 miles. According to that criterion it is said Super Moons occur this year on July 12, August 10, and September 8. Of these, the Moon is closest to Earth during this month’s perigee, a distance of just 221,765 miles. That compares to 224,175 miles on July 12^th, and 223,184 miles at the moment the Moon is full next month.

We must remember every month the Moon reaches a perigee location when it’s closest to Earth. The date and distance from Earth vary from month to month driven by a number of factors including position of the Sun. The Moon may be at any of its phases during the moment of perigee. Another specific time in the Moon’s monthly progression is when it’s at one of its four primary phases, such as when it’s “Full.” While the Moon may look really round and bright over a span of several days straddling its Full Moon moment, most observers (including me) find it very difficult to discern how close in time the Moon is to its actual instant of fullness when its center is 180 degrees of arc from the Sun measured along the ecliptic. On evening strolls in the park with my wife Andrea, we often enjoy views of what looks like a rising “Full Moon” even though it might be a day or two before or after the date the Moon is said to be full, such as on August 10.

August’s Full Moon occurs precisely at 2:09 EDT the afternoon of Sunday the tenth. That’s just 26 minutes after our lunar neighbor reaches the perigee point of its orbit, closest to Earth this month.

The Full Moon then is in Capricornus, one of the more southerly constellations of the zodiac. Expectations of seeing an especially big Moon on the tenth therefore have an added benefit of the lunar disk being rather low in the sky much of the night. That kicks into extra play the so-called Full Moon illusion – a perception we’re seeing a dramatically large lunar disk during times the Moon is at, or not too far from, the horizon.

The wide bright gibbous Moon many of us enjoyed last month the night before the scheduled Super Moon was indeed impressive. We argue it actually fit the bill for being called a Super Moon. The lunar distance that night at 10 pm was 223,541 miles, within the criterion of 224,851 miles and therefore near enough to be dubbed a Super Moon. But could that be if the calendar said Full Moon was the following day?

A “Full” Moon according to definition exists for just an instant, the transition moment dividing a week of waxing gibbous phases and the subsequent week of waning phases. Even if we see the Moon on a night when the almanac says it's full, unless we happen to be watching at the critical instant of fullness, we’re technically watching either a waxing or waning gibbous Moon.

For fun and pleasure let’s accept the rather arbitrary distance criterion for Super Moons, also keeping in mind the Moon is truly full for just an instant, and admit most of us can’t see much (or any) difference in the Moon’s roundness for a night or two around the date of the “Full” Moon, then we might enjoy looking at more than the one “official” Super Moon publicized for this month.

Imagination plays a big role in our impressions of the Moon, and super or not, like a rose – a name can affect perceptions of appearance.

The following shows center to center lunar distances from Earth during a five day span centered on Sunday August 10, the date of August’s “official” Super Moon. Note the Moon’s distances at sunset or lunar rise times for New York City. The popular definition of Super Moon is that they occur when the Moon is less than 224,851 miles from Earth.

Friday August 8 sunset in New York City is at 8:03 pm. Moon’s distance is then: 223,568 miles <224,851 miles, SUPER!

Saturday August 9 sunset is 8:02 pm. Moon’s distance at sunset: 222,097 miles <224,851 miles, SUPER!

Sunday August 10 Super “Full” Moon rises at 7:45 pm. Distance when it rises: 221,803 miles <224,851 miles, SUPER!

Monday August 11 Moonrise is 8:25 pm. Moon’s distance when it rises: 222,759 miles <224,851 miles SUPER!

Tuesday August 12 Moonrise is at 9:03 pm. Moon’s distance when it rises: 224,881 miles >224,851 miles close – but not “super”

The Perseids

After appreciating the beauty of an exceptionally large and bright Full Moon and some hardly less impressive gibbous phases, we must consider how the waning Moon affects observations of the wonderful Perseid Meteor shower peaking Monday evening into Tuesday morning August 11-12. Bright gibbous Moonlight washes out views of fainter meteors, but brighter examples may be seen every few minutes radiating across the sky from the direction of the constellation Perseus. That constellation rises above the northeastern horizon shortly before midnight. Perseid meteors are blazing streaks of light produced when bits of material from the core of comet 109P/Swift-Tuttle are heated to incandescence during their passages through Earth’s upper atmosphere at speeds of many thousands of miles per hour. While best views of this and other meteor showers are experienced as far as possible from artificial lights, this year we can’t do anything about the bright Moonlight affecting Perseid watching. As the Moon wanes, its rise time becomes later from night to night as the tail end of the Perseid shower may be seen tapering off.

Planets

During early morning of Monday August 18 look for brilliant Venus passing just 1/5 of a degree of arc from bright Jupiter.

The waning crescent Moon is near Jupiter in the pre-dawn sky of Saturday August 23. The next morning low in the eastern sky at about 5 a.m.,Venus has its turn with lunar rendezvous as this vivid planet now in its role as the “Morning Star”, forms a triangle with the Moon and far larger and more distant Jupiter.

Turning attention back to the evening sky, on Wednesday August 27, Mars is about four degrees from Saturn. Sunday evening the last day of the month the Moon appears close to Saturn in the constellation Libra.