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Moon Bumps: Earth's Gravity Creates Lunar Bulges

Earth's gravitational pull is so powerful that it creates a small bulge on the surface of the moon.

Earth's gravitational pull is so powerful that it creates a small bulge on the surface of the moon. For the first time, scientists have observed this bump from orbit, using NASA satellites.

The gravitational tug-of-war between Earth and the moon is enough to stretch both celestial bodies, so they each end up having a slight oval shape, with the tapered ends facing each other.

On Earth, this gravitational tension shows up in the form of tides. The moon's pull has a strong effect on Earth's oceans because water has so much freedom of movement. [The Moon: 10 Surprising Lunar Facts]

PHOTOS: Epic Views of Apollo's First Moon Rover

The corresponding distorting effect on the moon, called the lunar body tide, is more difficult to see, because the moon is solid except for a molten core. But Earth's pull raises a small bulge about 20 inches (50 centimeters) from the surface on the near side of the moon and a matching bulge on the far side.

"The deformation of the moon due to Earth's pull is very challenging to measure, but learning more about it gives us clues about the interior of the moon," Erwan Mazarico, a scientist who works at NASA's Goddard Space Flight Center, said in a statement.

The same side of the moon always faces Earth, but the bulge does move around a few inches over time, wobbling and following Earth's pull like a magnet, as the moon shifts slightly during its orbit.

PHOTOS: 'Blood Moon' Lunar Eclipse Dazzles North America

Scientists observed the lunar body tide using NASA's Lunar Reconnaissance Orbiter satellite, which is mapping the height of features on the moon's surface, and NASA's Gravity Recovery and Interior Laboratory satellite, which is mapping the moon's gravitational field. The satellites measured the height of 350,000 locations spread across areas of the moon closest to Earth and areas of the moon on the opposite side from Earth. The satellites passed over each location several times, so scientists could compare the height of each spot from one satellite pass to the next. By identifying which spots changed height, the researchers could track the lunar tide.

Scientists have studied the lunar body tide phenomenon from Earth, but this is the first time satellites have captured images of the lunar tide from orbit. The findings confirm the calculations scientists had already made from ground observations.

Originally published on Space.com.

How the Moon Formed: 5 Wild Lunar Theories Photos: Our Changing Moon Holy GRAIL! Photos From NASA's Moon Gravity Mission Copyright 2014 SPACE.com, a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

The remains of the Apollo 11 Lunar Module (LM) on the Moon's surface. The long shadow of the LM's landing gear is evident in the center of the image (NASA).

On July 16, 1969, Commander Neil Armstrong, Lunar Module Pilot Buzz Aldrin and Command Module Pilot Michael Collins launched atop a Saturn V rocket toward the moon. The 8-day NASA mission captivated the planet as Armstrong and Aldrin explored the lunar surface on July 20, supported by Michael Collins who orbited overhead. 46 years after the first successful landing of the Apollo program, we've dug into the NASA archives to find some familiar and some not-so-familiar views of the Apollo 11 mission. All photos and captions can be found in

NASA's Human Spaceflight Gallery

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Neil Armstrong leads the way across Pad A, Launch Complex 39 at Kennedy Space Center, Fla., during the Apollo 11 prelaunch countdown on July 16, 1969. Michael Collins follows behind.

The massive 363-feet tall Apollo 11 launched at 9:32 a.m. (EDT) on July 16, 1969, carrying Armstrong, Aldrin and Collins into the history books.

This photo was taken from a door-mounted camera on a U.S. Air Force EC-135N aircraft shortly after launch. The Saturn V second and third stages separate from the spent first (S-1C) stage, which then dropped into the Atlantic Ocean. Recently, the first stage engines were retrieved from the ocean floor by Amazon.com founder Jeff Bezos.

Earth is captured through the Apollo astronauts' camera lens on the way to the moon.

Earth shrinks as Apollo 11 continues its journey.

Aldrin looks into the TV camera during the third broadcast from space on the way to the moon.

The Apollo 11 Command and Service Modules (CSM) are photographed from the Lunar Module (LM) in lunar orbit during the Apollo 11 lunar landing mission.

After descending from the lunar module after a successful landing on July 20, 1969, Armstrong makes a bootprint in the loose lunar regolith. The astronauts' bootprints remain untouched on the dusty surface to this day.

Aldrin descends the steps of the Lunar Module ladder as he prepares to walk on the moon.

Armstrong and Aldrin deploy the American flag outside the lunar module "Eagle" at Tranquility Base in the Sea of Tranquility on July 20, 1969.

Aldrin prepares to deploy experiments on the lunar surface next to the large lunar module, "Eagle."

Aldrin oversees the deployment of the Early Apollo Scientific Experiments Package (EASEP), photographed by Armstrong during the crew extravehicular activity (EVA).

Aldrin stands next to one of the lunar module legs.

Armstrong inside the lunar module just after his famous moonwalk.

Collins photographs the returning lunar module with Armstrong and Aldrin inside. Soon after, the lunar module docked with the orbiting Command and Services Modules to begin the journey back to Earth.

Aldrin illustrates the gyroscope principle under zero-gravity conditions using a can of food in front of the TV cameras as the crew travel back to Earth from the moon.

The three Apollo 11 crew men await pickup by a helicopter from the USS Hornet, prime recovery ship for the lunar landing mission, after a fiery reentry and splashdown in the Pacific Ocean.

Mission Operations Control Room in the Mission Control Center, Building 30, Manned Spacecraft Center (MSC), showing the flight controllers celebrating the successful conclusion of the Apollo 11 lunar landing mission.

The Apollo 11 spacecraft Command Module and the Mobile Quarantine Facility are photographed aboard the USS Hornet.

Left to right: Armstrong, Aldrin and Collins, in a 21-day quarantine, are greeted by their wives.

New York City welcomes Apollo 11 crewmen in a showering of ticker tape down Broadway and Park Avenue in a parade termed as the largest in the city's history on Aug. 13, 1969.