Here's why:

* Weight is the force of gravity acting on an object's mass. It's a measure of how strongly gravity pulls on an object.

* Mass is the amount of matter in an object and remains constant.

Why weight changes with location:

* Gravitational Field Strength: The strength of the gravitational field varies depending on the mass of the celestial body and your distance from its center. For example, you weigh less on the Moon than on Earth because the Moon has less mass.

* Distance from Earth's Center: As you move further away from Earth's center, the gravitational force weakens, and your weight decreases. This is why astronauts in space are "weightless." They are still subject to Earth's gravity, but the distance is so great that the force is negligible.

Let me know if you'd like more information about gravity or weight!