Asked by: Stephen Newman, Foley, Alabama
This apparently simple question impinges on a fundamental axiom of physics: that there is no universal reference frame. So, when talking about the motion of the Earth, we have to declare which object the motion is with respect to.
For example, at the Earth’s equator you travel approximately 40,000km a day with respect to the Earth’s centre. Each day, the Earth’s orbit takes you about 2.5 million kilometres with respect to the Sun’s centre. And each day, the Earth moves about 19 million kilometres with respect to the centre of the Milky Way.
Finally, the Earth is also travelling about 47 million kilometres per day with respect to the ‘cosmic microwave background’ (CMB) – the leftover radiation from the birth of the Universe – which is perhaps the best surrogate we have for a universal reference frame. Since the directions of all these velocities are always changing, it would be meaningless to add them together.
- How far would we need to travel to leave our Galaxy?
- When I look to the stars, how far back am I seeing?
- How tall is the Universe?
- Where is the centre of the Universe?