Space & Innovation

The Moon's Gravity Alters Rainfall on Earth

It rains slightly less when the moon is high overhead. Continue reading →

When the moon is high overhead at night, its gravity actually can reduce the amount of rainfall very slightly, new research reveals.

In an article for Geophysical Research Letters, University of Washington scientists Tsubasa Kohyama and John M. Wallace report that the moon causes the Earth's atmosphere to bulge toward it. That causes the pressure, or weight of the atmosphere, on that side of the planet to go up, which in turn increases the temperature of air below.

Since warmer air can hold more moisture, the same parcels of air are now farther from their maximum moisture capacity, resulting in a slight dip in rainfall.

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The researchers studied 15 years of data collected by NASA and the Japan Aerospace Exploration Agency's Tropical Rainfall Measuring Mission satellite from 1998 to 2012. It proved that the rain is reduced by an amount that is measurable, though imperceptible to humans - a change of about 1 percent in the total rainfall variation.

"As far as I know, this is the first study to convincingly connect the tidal force of the moon with rainfall," said Tsubasa Kohyama, a doctoral student in atmospheric sciences.

While the effect isn't going to affect agriculture or alter weather forecasts, the knowledge is potentially beneficial to climate researchers, who can use it to test the physics behind their climate models.

The effect of the moon's position on air pressure on Earth was first detected back in 1847, and researchers showed in 1932 that the moon could affect air temperature as well. A 2014 study by the same University of Washington researchers confirmed that air pressure on Earth varies with the position of the moon.

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Wallace plans to conduct future studies to see whether certain types of rain storms, such as heavy downpours, are more susceptible to the moon's position, and whether the moon has any effect on the frequency of storms.

The Moon’s tug on the Earth’s atmosphere has a slight but measurable effect on rainfall.

There's no denying it, the "supermoon lunar eclipse" didn't disappoint. A large swathe of the planet was treated to a rare lunar event on Sunday night and early Monday morning when a so-called "supermoon" coincided with a lunar eclipse. Neither of these astronomical events are particularly rare in their own right, but their coincidence hasn't happened since 1982 and won't happen again until 2033.

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Although clouds interrupted most of totality in my location (near Los Angeles, Calif.), I was lucky enough to spot the beautiful "blood moon" for a short time and, later, the bright disk of a supermoon. Here I've collected some supermoon lunar eclipse photos from around the world, including my own. If you want to have your astronomical shots featured, send them to ian_oneill@discovery.com, or tweet me at

@astroengine

or

@Discovery_Space

.

Clouds were tricky over Los Angeles, Calif., where total lunar eclipse was often obscured by cloud, as shown in this view over the Griffith Observatory.

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It just so happens that last night's supermoon was also a "Harvest Moon" -- the closest full moon to the autumnal equinox.

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Photo: The lunar eclipse over Windsor Castle, Berkshire, UK, in the early hours of Monday morning.

During a lunar eclipse, the Earth is between the sun and the moon, but the moon still receives sunlight that refracts through our planet's atmosphere, often turning the moon deep red or orange. This is not why some eclipses are called "blood moons," however. A blood moon is the last total lunar eclipse of 4 successive total lunar eclipses (with no partial lunar eclipses in between), each of which is separated by 6 lunar months. For more information on the "lunar tetrad",

see EarthSky.org

.

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Photo: The supermoon lunar eclipse begins to set over Gaza.

The supermoon sets over Sydney, Australia, before the lunar eclipse commenced. Unfortunately for Australia (and much of Asia), the eclipse occurred on the other side of the planet.

The supermoon lunar eclipse at totality in clear skies over Jerusalem, Israel.

The supermoon lunar eclipse over Rio de Janeiro, Brazil.

Clouds block a clear view of the supermoon eclipse over New York.

Clear skies over Cape Town, South Africa, provided sharp views of totality.

The supermoon eclipse hangs over statues in Venice, Italy.

As the supermoon slipped out of totality, sunlight reflected bright off the moon's surface, ending the last supermoon eclipse until 2033.

The total lunar eclipse comes to an end over Cape Town, South Africa.

After the lunar eclipse, the supermoon continued through the night. Although the term "supermoon" sounds grand, it is a bit overstated. As the moon orbits the Earth in a slightly eccentric path, the Earth-moon distance varies by approximately 30,000 miles, making a full moon appear 14% bigger in the night sky at the point of closest approach (perigee) compared with the point of furthest extent (apogee). Still, the moon can shine up to 30% brighter, making a supermoon appear brighter than normal.

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Photo: The supermoon on Sunday night (local time) after lunar eclipse over Woodland Hills, Calif.