Scientists have known for a long time that the gravitational pull between the Earth and the moon have warped both bodies to look slightly egg-like in shape, but new data collected from NASA missions is revealing just how that pull is affecting the moon.
MIT scientist Erwan Mazarico, who works at NASA's Goddard Space Flight Center, explains that "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." NASA explains:
Earth’s distorting effect on the moon, called the lunar body tide, is... difficult to detect, because the moon is solid except for its small core. Even so, there is enough force to raise a bulge about 20 inches (51 centimeters) high on the near side of the moon and similar one on the far side. The position of the bulge actually shifts a few inches over time. Although the same side of the moon constantly faces Earth, because of the tilt and shape of the moon’s orbit, the side facing Earth appears to wobble.
While we see the moon wobbling, the moon sees us dancing, according to NASA:
From the moon’s viewpoint, Earth doesn’t sit motionless but moves around within a small patch of sky. The bulge responds to Earth’s movements like a dance partner, following wherever the lead goes.
Which is kind of wonderful. NASA says that the new, more detailed information comes from data collected on two missions — the Lunar Reconnaissance Orbiter, which has spent five years looking at the moon from a close orbit, and the Gravity Recovery and Interior Laboratory mission — and recorded in a paper published online at Geophysical Research Letters.