It seems that Tom has given up this argument. However, Max, I am very interested to hear more about these "independent methods" of determining the AU. If the AU can be verified without assuming the sphericity of the Earth, then it proves that Rowbotham's much smaller value for the distance between the Earth and Sun is incorrect. This would greatly damage the FE position. Can you shed more light on this?
Of course Humboldt.
There are many common ways of measuring the AU that have been known since the 1800's. But one of the more modern ones stands out in the sense that it doesn't assume anything about the Earth's shape or motion.
It involves the use of radar ranging. Radar is no good for really distant objects, like the stars or outer planets. But it works quite well with the inner solar system.
Basically, we transmit a train of radio waves in the direction of another object in our solar system, and measure how long it takes for us to hear the "echo". By multiplying this round trip time by the speed of light (300,000 km/s) we get twice the distance between the object and us.
Unfortunately, measuring the AU with this method is a little difficult because we can't bounce radio waves directly off of the sun. The sun (being a superheated gas) tends to absorb radio waves rather than reflect them. So it's not as simple as pointing a radio transmitter at the sun and measuring the distance.
Fortunately, we don't have to do this. We can use the planets.
Even if we don't assume that
all the planets orbit the sun (Which many FE'ers don't) we do know that
at minimum Mercury and Venus do orbit the sun. We know this because at regular intervals, we can watch Mercury and Venus pass in front of and behind the sun.
Venus is a very common target for radar ranging, and we know how far it is away from Earth at its smallest distance (about 45,000,000 km) and we know how far away it is from Earth at its greatest distance (345,000,000 km.)
Since Venus' orbit is known to be circular (the most circular of all the inner planets, in fact) we know the sun must lie in the middle of the two extremes. Do the math, and you get a value for the AU around 150,000,000 kms.
Even if some die-hard FE'er won't accept this as a measurement of the AU, it should still be pointed out that Venus occasionally transits the sun at its closest aproach.
Even then, it is known that Venus is many times farther away from the Earth than the FE'ers claim, and since it is clearly in front of the sun, it implies that the sun must be many times farther away as well. So even if FE'ers won't accept the details of this argument, it is still a qualitative demonstration that the Sun must be at least 45,000,000 kilometers away.
It's also possible to prove the Earths orbital motion around the sun by the observation of the aberration of starlight, but I'll save that for another post!
I also want to point out that all this, while important, doesn't have much to do with the topic at hand.
The topic is extra-solar planets. Accurate measurements of the AU are only really important if we are measuring a distance via stellar parallax, as Tom Bishop has asserted (incorrectly.) But as I have said before, the detection of Gliese 581-c is a valid scientific discovery regardless of the Earth shape or motion, as it was in no way reliant on measurements of stellar parallax to make it's observations.