Here's why:

* Gravity: Earth has a much stronger gravitational pull than the Moon. This means the force pulling an astronaut towards Earth is much greater.

* Weight vs. Mass: Weight is the force of gravity acting on an object's mass. While an astronaut's mass remains the same on both Earth and the Moon, their weight changes due to the different gravitational forces.

So, even though an astronaut's mass stays the same, they would experience a much lower weight on the Moon due to its weaker gravity.