In 1610, Galileo Galilei observed the moons of Jupiter rotating around it. He described them as small planets orbiting a larger planet—a description (and observation) that was very difficult for the church to accept, as it challenged a geocentric model where everything was supposed to revolve around the Earth. This observation also showed that the planets (Jupiter, Neptune, and later Venus was observed too) are all spherical, and all orbit the sun.
where P and T are the pressure and temperature of air, and P0 and T0 are the standard values of one atmosphere of pressure and 300K. Since with mirages there is no appreciable height difference, pressure differences are negligible, and so the temperature difference dominates differences in the index of refraction. When light travels from one medium to another, the path of the light is refracted, or bent. This is what causes the “bent stick” appearance of a long object partially inserted in water, such as a pole placed into the water of a pool. This behavior is described by Snell’s law:
2. Another related thing I don’t understand: if the sun and moon are always above the disk of the Earth, why can’t everyone in the world see them at all times? Surely they should always be visible, at least at a low angle. I can’t draw myself any diagram where they are not always visible, but we see that that doesn’t happen. I can’t see how night time happens. Help!
43.) The circumstances which attend bodies which are caused merely to fall from a great height prove nothing as to the motion or stability of the Earth, since the object, if it be on a thing that is in motion, will participate in that motion; but, if an object be thrown, upwards from a body at rest, and, again, from a body in motion, the circumstances attending its descent will be very different. In the former case, it will fall, if thrown vertically upwards, at the place from whence it was projected; in the latter case, it will fall behind the moving body from which it is thrown will leave it in the rear. Now, fix a gun, muzzle upwards, accurately, in the ground; fire off a projectile; and it will fall by the gun. If the Earth traveled eleven hundred miles a minute, the projectile would fall behind the gun, in the opposite direction to that of the supposed motion. Since, then, this is NOT the case, in fact, the Earth's fancied motion is negatived and we have a proof that the Earth is not a, globe.