Though the Earth's natural satellite, moon, looks huge and perfectly round in the skies, it's not completely round. The gravitational pull of the earth causes the moon to appear distorted.

Though, scientists were aware of this phenomenon, it's not something that could be easily observed from Earth or while orbiting Earth. But when Erwan Mazarico, lead author of the study and a scientist from the Massachusetts Institute of Technology in Cambridge, Mass. along with his colleagues combined the high-definition data received from two of the NASA spacecraft missions - the Lunar Reconnaissance Orbiter (LRO) and the Gravity Recovery and Interior Laboratory (GRAIL), they understood the gravitational pull involved in the moon's distortation. The new study could help scientist to understand the internal composition of the moon.

"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," Mazarico, who works at NASA's Goddard Space Flight Center in Greenbelt, Md. said in a press release.

The images of the moon collected by these spacecrafts clearly revealed how the structure of the moon changed with Earth's gravitational pull. The scientists analyzed the images and selected 350,000 sites covering the near and far sides of the moon.

The mutual pull between the Earth and the moon greatly affects the oceans and causes high and low tides.

Scientists have found that the Earth's effect on moon is called lunar body tide and it results in swelling of the moon by about 20 inches. The swell changes over time and travels depending on the movement made by the Earth.

"If nothing changed on the moon - if there were no lunar body tide or if its tide were completely static - then every time scientists measured the surface height at a particular location, they would get the same value," said Mike Barker, the co-author of the study.

Earlier, researchers have measured the height of the locations to find changes, but this is for the first time that high resolution pictures were used revealing the lunar tides.

A vital step in the process was to locate exactly how where LRO was situated for each measurement. In order to reconstruct the spacecraft's orbit with adequate accuracy, the researchers needed the detailed record of the moon's gravitational field, which was provided by the GRAIL mission.

"This study provides a more direct measurement of the lunar body tide and much more comprehensive coverage than has been achieved before," John Keller, LRO project scientist at Goddard, added.

"This research shows the power of bringing together the capabilities of two missions. The extraction of the tide from the LOLA data would have been impossible without the gravity model of the moon provided by the GRAIL mission," said David Smith, the principal investigator for LRO's LOLA instrument and the deputy principal investigator for the GRAIL mission.

The detailed study were published in the journal Geophysical Research Letters.