New answers tagged

10

To understand the answer provided below, we need to reframe the original question slightly. Perhaps a better way to put "was libration first predicted" is to say, outright, libration was first observed, then a theory was advanced explaining its occurrence. Although the observation of libration is documented in 1632 by Galileo, and independently ...


6

According to Wood Galileo was the first to observe libration in longitude and latitude and make notes of it, described in his Siderus Nuncius. Given that exact observations, and comparisons require detailed photos or images, it seems unlikely that this libration was observed earlier. An interesting read on the discussion among the leading scientists around ...


18

The variable speed of the Moon on the celestial sphere has been known since ancient times. The Babylonians made ~7 centuries of daily astronomical observations from around 700 BC. That data was the basis of the astronomical tables of Hipparchus, which Ptolemy used in creating the formulae of celestial motions in the Almagest. However, actually observing the ...


5

The rotation of our Milky Way in general is derived from observations of the kinematics of gas and stars throughout our galaxy. See for instance a recent compilation of Milky Way rotation curve data from which this figure is taken The rotation curve of the Milky Way as derived from gas kinematics (blue), star kinematics (orange) and masers (black).


5

The great scientist Johannes Kepler wrote a very unusual work called Somnium ("The Dream"). It is sort of a cross between a science fiction story and a scientific description of the Moon. Somnium began as a student dissertation in which Kepler defended the Copernican doctrine of the motion of the Earth, suggesting that an observer on the Moon ...


3

ds refers to a distance in spacetime (this includes time). Just as, in classical physics, you see $$ds^2=dx^2+dy^2+dz^2$$ for any given line element, in spacetime you get similar things going on. For flat spacetime, this gives some good intuitive understanding. Depending on your signature, an element in flat (Minkowski) spacetime is $$ds^2=dt^2-dx^2-dy^2-dz^...


Top 50 recent answers are included