The Moon is getting farther away every year. The Moon exerts a pull on Earth, causing our planet to be slightly egg-shaped. It affects water even more, creating tides and causing the oceans to pile up towards one side of the planet, forming a ‘tidal bulge’. This bulge is dragged around with the Moon as it orbits. As Earth rotates faster than the Moon – 24 hours versus 27.3 days – the bulge moves slightly ahead of the Moon’s position in orbit. The Moon pulls back on it, effectively trying to slow it down and causing Earth’s rotation rate to gradually slow down over time as a result. As the two bodies interact through gravity, this tugging causes Earth to lose energy while the Moon gains energy. Because of this energy boost the Moon is slowly spiralling outwards, moving away from us by 3.8cm per year.
100 Mind-Blowing Bulge’ Facts
Earth isn’t round. While this sounds like an elaborate joke, we’re serious. Earth isn’t flat, but it’s not perfectly round either. Earth’s rotation causes the planet to bulge at the equator and flatten at the poles, while the distribution of mass on Earth (which is not perfectly uniform) causes small variations in the gravitational pull at different locations on the planet. These variations are too small to be seen in pictures of Earth from space, so they appear round to the human eye. The shape seen in the video above is not technically the shape of the planet, but its ‘geoid’, the shape of its mean sea-level surface extending around the entire globe. The map was produced using data collected from ESA’s Gravity and Steady-State Ocean Circulation Explorer (GOCE) and shows the most detailed map ever created of Earth’s gravity field.
The Moon is drifting away from Earth. You read that correctly! The Moon is gradually drifting away from Earth at a rate of approximately 4 cm per year. This phenomenon is caused by the Moon pulling on Earth’s oceans creating tidal forces that produce a bulge of water on the side of Earth facing the Moon. This bulge in turn creates a gravitational pull on the Moon, causing it to accelerate slightly and move further away from Earth. Over time, this process has caused the Moon to move farther away from Earth each year. This gradual drift is not noticeable on a day-to-day basis, but over millions of years, it can have significant effects on Earth’s rotation. Today, most scientists believe the Moon is ‘Earth’s child’ – a large body collided with Earth, destroying our planet’s mantle and sending material into orbit from which the Moon formed. This ‘big splash’ theory would explain why the Moon’s rocks are similar to those on Earth. Bonus fun fact: Australia is wider than the Moon. The Moon sits at 3400 km in diameter, while Australia’s diameter from east to west is almost 4000 km. The Moon, as a sphere, has more surface area, but it’s still pretty impressive.