On March 19, 2011 when the Moon loomed to its closest approach to Earth in almost 20 years, the usual gang of doomsayers spewed forth apocalyptic predictions while seeking to link the Extreme Supermoon event with recent natural disasters in New Zealand and Japan. While science has shown the Chicken Little’s laid a colossal egg, at least we were given a plethora of marvelous moon photos to swoon over.
Moon River, Wider than a Mile
(image via: Global Times)
With apologies to Johnny Mercer and Andy Williams, the March 19, 2011 extreme supermoon looked more than a mile wider than the average moon and actually WAS miles closer. Though the moon’s distance from the Earth (measured center to center) varies between 357,000 kilometers (222,000 mi) at perigee and 406,000 km (252,000 mi) at apogee due to the elliptic nature of the lunar orbit, the March 19 event saw our solitary satellite snuggle up to within a mere 356,577 km (221,572 mi). Since the average lunar perigee is 364,397 km (226,432 mi), on March 19 the moon was about 7,820 km (4,860 mi) closer to the earth. Above is the March 19 supermoon rising behind Berlin’s Funkturm radio and television tower.
It gets even better. Supermoons are most notable when they occur at what astronomers call “perigee-syzygy”: a full or new moon that coincides with lunar perigee. While this in itself isn’t all that special (run of the mill supermoons occur 4 to 6 times a year), so-called “extreme supermoons” like this year’s one looming over Sofia, Bulgaria (above, top) are a different story.
There have been 14 extreme supermoons since 1900 with the most recent occurring in 2005, 1993, 1992, 1990, 1975, 1974, 1972 and 1954. We can look forward to enjoying (weather permitting) future extreme supermoons in 2016, 2018, 2023, 2034 and 2036… so save the date, we’re brewin’ up some moonshine!
Here’s a short video primer on supermoons and supermoon-mania by some folks who know a thing or two about the moon… NASA:
(image via: Wikipedia)
Numbers are all well and good but are these differences in distance actually noticeable from our Earthly vantage point? Indeed they are. The average full moon at perigee appears around 12 percent larger than an average non-perigee full moon. Supermoons, even more so. The difference is even greater for extreme supermoons such as the March 19, 2011 event as shown in the comparison split-screen image above. It’s estimated that the moon appeared 14 percent larger and was 30 percent brighter!
The Tides That Bind
For those of us on Earth (basically ALL of us, ISS-crew excepted), the moon’s gravitational force is most evident in the way it influences the tides. One might expect an extreme supermoon to induce some extreme tides, and indeed that’s the case though “extreme” is a relative term; up to 15 cm (6 in) depending on local conditions.
Tidal forces also affect land masses though not enough to be noticeable. That’s not the case on some of the solar system’s other heavenly bodies, specifically the moons which orbit large gas giant planets. These moons heat up from the constant stress and stretching; Jupiter’s moon Io is a leading example. Other moons affected by tidal forces are Enceladus (Saturn) and Triton (Neptune).
Where we run into problems of speculation and extrapolation is when we try to apply marine tidal dynamics to land masses. The forces involved with plate tectonics and earthquakes are not affected by lunar tides, not to mention that old favorite of astrologers: the alignment of the planets.
Some attempts have been made to show causal relationships between the January 10, 2005 extreme supermoon and the December 26, 2004 Indian Ocean Earthquake and tsunami in Indonesia as well as the March 19, 2011 extreme supermoon and the March 11, 2011 Great Tohoku Kanto Earthquake and tsunami in Japan. Not so fast: it’s been proven unequivocally that “the 2011 Tohoku earthquake is the only destructive earthquake of 8.0 magnitude or greater to have occurred within 2 weeks of the 14 extreme supermoons from 1900 to the present date.”
“I’m Ready For My Closeup”
(images via: Ajorbahman’s Collection)
When the moon hits your eye like a big pizza pie, that’s amore! Or to be more precise, that’s an extreme supermoon! Hmm, maybe it’d sound better if Dino sang it. In any case, you may have noticed the vast majority of the photos that accompany articles on the supermoon feature the moon’s face hovering just above the horizon. There’s a good reason for that: supermoon or not, the moon just looks bigger when it’s rising or setting.
It isn’t really bigger, of course. Our brain’s visual centers aren’t equipped to accurately judge the distance of objects, especially those as distant as the moon. Instead, we compare the relative sizes of objects sharing the same field of vision. A full moon riding high in the sky looks smaller than one rising up from behind a city skyline because there aren’t any visual cues for comparison – clouds and stars don’t count. The same theory can be applied to rising and setting suns.
Everything said up to this point applies to supermoons seen by human beings – including our primitive ancestors. Go much farther back in time and a lot of what those aforementioned doomsayers have been saying takes on more than a glimmer of truth. That’s because the moon didn’t always orbit the Earth at its current, slightly variable distance. It used to be closer… a LOT closer.
Astronomers believe the moon was formed by a spectacular collision between the Earth and a Mars-sized rogue planetoid approximately 4.5 billion years ago, very early in the history of the solar system. The impactor slammed into the mostly molten proto-Earth, splashing a goodly glop of magma into space where it first became a Saturn-like ring before coalescing into the moon.
(image via: Science Photo Library)
The newborn moon orbited exceptionally close to the earth – approximately 25,500 km (15,845 mi) away. Imagine the tides a moon that close would raise on an Earth awash with oceans of magma! The moon continues to slowly spiral away from the Earth at a rate of about 3.8 cm (1.52 in) per year, thus making each future supermoon slightly less super than the one before.
(image via: ScriptingNews)
So you missed the 2011 extreme supermoon due to cloudy skies in your area; not to worry. There’ll be another one soon enough… well, 2016 isn’t that far away. Maybe you, like the future President of the United States, will be able to see it from your house. Hey, that’s no moon!