What does apparent and absolute motion mean in astronomy?

Question

Levi Acosta · Accepted Answer

What appears as movement to observer is apparent motion. Any apparent motion is with reference to a moving frame. Absolute frame for absolute motion in astronomy is still a mirage.

The frame of reference is a frame, at your position, with directions that appear to be fixed in your view. This is observer-centric apparent motion. Similarly, there are Earth-centric, Sun-centric, Milky Way-centric,... apparent motions. As observers, we see the Moon, other planets, our star, Sun, and other stars moving, at different speeds. This is apparent motion. The fitting of an absolute frame of reference for an absolute motion and the continuous marking of the space (relatively) vacated by everything at any given time remain open challenges.

HIX Tutor · Answer

undefined Great question! Let's break it down step by step.

1. **What is motion?** 
   Motion means that something is moving.

2. **What is apparent motion?** 
   Apparent motion is how we see things move from Earth. For example, the sun looks like it moves across the sky. This is how we, as observers, see it.

3. **What is absolute motion?** 
   Absolute motion means the true movement of an object in space. This looks at how things move in relation to everything else in the universe, like stars and galaxies.

4. **An example to think about:** 
   Imagine you're in a car. If you see a tree moving fast, it might seem like the tree is moving. But really, it’s you that is moving!

5. **Why is this important in astronomy?** 
   Understanding both kinds of motion helps astronomers know how objects like planets and stars move in space.

Do you see how apparent and absolute motion are different?

John Alexander · Answer

undefined Apparent motion in astronomy refers to the perceived movement of celestial objects across the sky as observed from Earth, caused by Earth's rotation and orbit. Absolute motion, on the other hand, refers to the actual motion of celestial objects through space relative to a fixed point, such as the center of the Milky Way galaxy or the cosmic microwave background radiation.