I remember a friend of mine, Ken Webb, never really understood the nature of scientific theories. For him, science was about facts, and those were permanent. True, new facts could be discovered, but the existing facts remained solidly present.
As a result, he never liked Patrick Moore. "He's always changing what he is saying", he would complain to me, as if Patrick Moore was somehow guilty of purveying false information to people deliberately. But of course astronomy, especially during that time, was full of false information. Mercury did not rotate, but we now know that it does. Venus was probably a humid watery planet, but we now know it as a super heated hell hole of a planet, a runaway greenhouse world without water.
At one point, astronomers calculated the small perturbations in Mercury's orbit suggested another planet, as yet unseen, between Mercury and the sun, which was given the name Vulcan (this was way before Mr Spock!). After all unexpected changes in the orbit of Uranus led Alexis Bouvard to deduce that its orbit was subject to gravitational perturbation by an unknown planet, and hence the discovery of Neptune. But in fact, it was the strength of the suns gravitational field alone which was causing such anomalies, and Einstein's General Theory of Relativity explained the orbit without recourse to that planet. In fact, the magnitude of the differences of General Relativity from Newtonian theory diminishes rapidly as one gets farther from the Sun, and is largely negligible for other planets.
New means of measuring, and better measurements, mean that astronomical knowledge changes, and sometimes that means that established facts are overturned. That's the nature of science, and it is not just in astronomy. The very idea that the earth had tectonic plates, and continents drifted over time was once mocked; now it is simply part of our mental makeup, so much as known that we forget how strange the idea must have been when it was first mooted. And that has also led astronomers to reassess other planets, to see if they have tectonic plates, and the theory has been developed further as a result. At first, it was believed that Venus had a lack of plate tectonics, because the oceanic hallmarks of continental plates - spreading ridges, subduction zones and transform faults - were not found on Venus, but these are oceanic hallmarks, not found on land masses, and the surface of Venus does not represent oceans but continental land masses, where we find rift zones, mountain belts, and strike-slip systems.
Astronomy is an every changing science, and Patrick Moore kept up to date. As new discoveries came along, he shared them in "The Sky at Night". And it throws up surprises all the time; what seemed to be the solid facts of the 1950s have often remained in place, but sometimes they also changed as new and improved theories change the way we understand the universe.
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