If the moon were half its mass, then the ocean tides would have been correspondingly smaller and imparted less energy to it. So a less massive moon would nonetheless end up closer than the real one to Earth. The energy given to the moon comes from Earth’s rotation—and to compensate, our planet is slowing down.

Use in astronomy

Can we use the Hubble Space Telescope to see anything left behind by the astronauts? Yes, the flag is still on the moon, but you can’t see it using a telescope. The flag is 125 cm (4 feet) long, and you would need an optical wavelength telescope around 200 meters (~650 feet) in diameter to see it.

– Shallow moonquakes, quakes at the surface of the moon (20-30 kilometers deep), likely caused when the moon’s crust slips and cracks due to the gradual shrinking or “raisining” of the moon as it cools. – Meteor impacts, vibrations caused when meteors crash into the surface of the moon.

In just eight years, we had gone from zero human spaceflight capability to landing men on the surface of the moon. From these missions, scientists developed a new view of the origin and evolution of the planets and of life on Earth. Their visual observations added to the burgeoning knowledge of lunar geology.

When energy propagates across such a compressible structure, it acts like a foam sponge—it deadens the vibrations.” Even the biggest earthquakes stop shaking in less than 2 minutes. The moon, however, is dry, cool and mostly rigid, like a chunk of stone or iron.

The Moon’s mantle, too cool to move easily, has no convection and no active tectonic plate motions.