Bisbee daily review., 1911-06-17
WHY WE THINK THE
 EARTH MOVES
THE
(scienti.lc Ame-icnn

(Scienti:ic American
 II. H. asks. This question was
 Aaied me by one of In ou-,. men today; How do scientists know and prove that the earth revolves around the sun, and that the sun stands sul2 being the assistant super . intencen. Of this tannery, and more { interested in the manufacture of sole ] leather than astronomy, l was unable ! 10 give him satisfactory answer ! ! would be very much pleased ii you could answer this question in your | Votes and Queries. A It is bv no means easy to prove that the earth : goes around the sun in a year. in- stead of the opposite statement that the sun goes around the earth in a year The appearance of the sky IS that the sun moves around the earth, and for many centuries men ! believed this to be the case. The stars which are now in ese east in early evening are seen night by night to be higher above the horizon at the same hour until they pass quite across the sky and disappear from our view for six months. This motion is as well accounted for by supposing that the sun is in motion toward the east as by what is now known to be the true statement that the earth Is mOvng aorund the sun toward the east Until the telescope was invented it was generally be hcyed that the earth was the center oi the suns motion although there were some who held the opposite view. One view or the other must he true. There is no third possibility. There are. however, two phenomena. which could not be detected except by the use of the telescope because of their minuteness, which are con elusive proof that the earth is in motion, and then we know that the sun is the center Of the earths mo ton. They are the liberation of Light and the Annual Parallax of the Stars. Neither of these is easy of explanation, except in scientific terms. By the alteration of light Is meant that the stars are not seeD-4u their true places. but are thrown a little in front of their true places by a combination of the motion of their light toward us and the mo ton of the earth in it's orbit around the sun. All stars share this disap- pOintment excepting only those fin the line of the earth's motion at any time. If we are going directly to ward or from a star, it is seen in It's true place. But if a star is away on the right or left hand Of the earth's line of motion. the star seems to be a little in front Of it's real position. This is well illustrated by
 Tainfalling vertically down while we ride rapidly through the shower
 Our motion causes the rain to seem to fall towards us from in front of us. This displacement of the stars is so slight that it can only be made out by the most careful measure ments by the telescope. Yet it is very real. and could not take place unless the earth were in motion and the light of the stars also in motion
 toward us. Since 1t is the same for all stars, it certainly has its origin in the earth and not in the stars. The annual parallax of the stars is caused by the fact that the earth makes a huge curve in space as it goes around at a distance of 93 millions of miles from the sun. The diameter of the earths orbit is about 1s0. .000. 900 miles. It is today a vast and inconceiyabie distance away iIOH IuS Didct III space where IT vas six months ago. We thus view the stars from points widely seps- rated every six months. and if the stars were not at distance from us vastly greater than this enormous distance. we could see them change their places with reference to each other as the year advances. By min ute measurements carried on for many years. certain of the stars have been found to have just the change of place required by such a motion of the earth. Tn this way the distances of from forty to fifty stars have been determined in the last one hundred years of constant labor on the part of our best astron- r7aers. There is another argument which is Of force here. although not relied upon as a proof that the earth fevolves around the sun. It is that the sun is so much larger than the earth that it controls the motion of the earth just as 1t does that of the other planets which we can see reyolve around the sun. in the same way as the earth controls the mo ton of the rsoon. It .S zSs possible that the sun can revolve around the earth, under a law of attraction such as prevails among the heavenly bodies. The larger always controls