[g__day (Matthew)]

Science thought for the day.

A simple experiment - ask someone to point to the Sun. Now ask them to point not where they see the Sun, but exactly where the Sun actually it is. It's easy to do - just advance your aim four Sun diameters (or two degrees) ahead of where it appears in the sky.

The maths is fairly simple. The Sun is about 8 light minutes away from Earth and about 30 arc minutes wide and the Earth rotates at 15 degrees an hour (360 degrees / 24 or 15 arc miniutes a minute if you like). So in the eight minutes it takes light from the Sun to reach the Earth the Sun's true position is actually 15 / (60 / 8) = 2 arc minutes or four Sun diameters ahead of where you see it.

This should give folk an easy way to confirm a gravitation field re-shapes or radiates (shudder) at the speed of light; as a sensitive gravitometer orbiting the Earth would show the centre of mass for the Sun to be where the Sun appears visually - not where it is absolutely.

Science can challenge what seems fundametally apparent - cool hey!