Astronomy Experiment: Measure Earth's Trajectory

In a recent discussion, someone asserted that gravitic effects travel with a
finite propagation delay. Another person said that this notion would make
impossible stable orbits. The logic behind both arguments seems somewhat
convincing, and brings to mind an old experiment on gravity:

Hypothesis: The effect known as gravity is instantaneous. Null hypothesis:
Gravitic effect travels at a finite speed comperable to the speed of light.

Experiment: If gravity travels similar to light, then the trajectory of
planet Earth should be a tangent to the observed location of the Sun (eight
minutes west of 'current' position). If gravity is instantaneous, then the
trajectory of planet Earth should be a tangent to the current position of
the Sun, eight minutes east of observed.

Question: Do we have at our disposal equipment that can measure this
difference in trajectory? Location of planets, pulsar timings? Preferably
equipment that is not restricted to authority figures; usable by ameteur
astronomers.

Interesting question, but probably instruments would need to be much
more sensitive than amateur-grade to measure what you want to measure.
You might like to read some about general relativity, which describes
gravity not as a field that propagates, but as a curvature of space
due to massive objects. It includes the idea that rotating objects
like planets and black holes sort of drag the curvature of space
around. There might be something in a discussion of this that answers
the question of how fast gravity (space-time distortion) propagates.
This dragging would become easily measurable only near a very fast
heavy spinning object, I think.

I'm no expert, just basing these remarks on science articles for
everyday readers.


AngleWyrm wrote:
In a recent discussion, someone asserted that gravitic effects travel with a
finite propagation delay. Another person said that this notion would make
impossible stable orbits. The logic behind both arguments seems somewhat
convincing, and brings to mind an old experiment on gravity:

Hypothesis: The effect known as gravity is instantaneous. Null hypothesis:
Gravitic effect travels at a finite speed comperable to the speed of light.

Experiment: If gravity travels similar to light, then the trajectory of
planet Earth should be a tangent to the observed location of the Sun (eight
minutes west of 'current' position). If gravity is instantaneous, then the
trajectory of planet Earth should be a tangent to the current position of
the Sun, eight minutes east of observed.

Question: Do we have at our disposal equipment that can measure this
difference in trajectory? Location of planets, pulsar timings? Preferably
equipment that is not restricted to authority figures; usable by ameteur
astronomers.