How We Know The Earth Moves (1960)

[Music] we live on a planet called a tiny speck of land water and gas in the vastness of space we've been told a number of things about our planet home we've been told that it spins or rotates on its axis and we've also been told that it travels around the Sun but how do we know these statements are true to find out let's consider the movements one at a time first how do we know the earth rotates thousands of years ago the ancient Greeks studied their world it didn't seem to move at all but at night when they looked at the sky they noticed that the Stars seemed to move all the stars moved in a circle around one star the North Star how could the movement of the stars be explained as this model shows either the stars move in circles around the North Star or the stars only seemed to move because the earth turns under them many people guessed that it was the earth that turned but no one could prove it finally about 100 years ago a French scientist named Foucault found a way to prove that the earth turns he used a free swinging pendulum this drawing of Foucault pendulum appeared in a newspaper of the period to understand fucose proof let's look first at this model of a pendulum and the earth as we set the pendulum moving we start the globe turning although the globe rotates notice that the pendulum keeps swinging in the paths in which it was started the turning globe does not change the direction of the pendulum swing in some museums we can observe a full-scale Foucault pendulum we have seen that a free swinging pendulum keeps swinging in the direction in which it was started but this pendulum appears to change the direction of its swing striking one peg after another the explanation must be that the earth is turning under it so Foucault proved that the earth spins it spins or rotates once in about 24 hours but we've also been told that as it rotates the earth travels or revolves around the Sun how do we know the Gulf's around the Sun the answer comes from the Stars ancient astronomers noticed that the Stars appear in patterns or constellations in the sky they gave them names representing different creatures Scorpius the scorpion Sagittarius the Archer Capricornus the goat and many others they also noticed that the Sun sets in front of a different constellation each month of the year and since the same constellations reappear every 12 months they mapped them in a circle like this but they made the mistake of thinking that the Sun moved around the earth between the earth and the stars many centuries later however an astronomer named Copernicus said that the Sun only seems to set in front of different constellations he said the Sun doesn't move at all instead the earth moves around the Sun his reasoning may be illustrated in this way imagine that this fire is the Sun each group of people represents a different group of stars this man represents the earth as the man moves around the fire he sees different groups of people behind it in the same way as the earth moves around the Sun we see the Sun against different groups of stars so the Sun appears to set in front of different constellations because of the Earth's yearly journey around the Sun today powerful telescopes have helped astronomers prove that the earth circles the Sun by attaching cameras to telescopes astronomers take pictures of the stars at different times of the year comparing these pictures they have found that nearby stars seem to move or shift in relation to distant ones to understand how this movement helps astronomers prove that the earth circles the Sun let's do an experiment together first we'll show you what to do after we show you you can try it yourself you will hold up your finger at arm's length like this and imagine that your finger is a nearby star then you will look at a distant star on this screen next you will close one eye like this and cover the star on the screen with your finger like this finally keeping your eye closed and your finger still you will move your head around in a circle as shown here now let's try it ready go here's the star close one eye and cover the star with your finger keep your finger still and roll your head as you roll your head notice that your finger appears to circle or shift back and forth from one side of the star to the other your finger doesn't really move it just seems to move because you look at your finger from different directions as your head moves astronomers have noticed that near stars seem to shift back and forth in relation to distant stars just as your finger seemed to shift because your head moved so the near Stars seem to shift because the earth moves by studying and measuring this star shift astronomers have shown that the earth follows an almost circular path as it revolves around the Sun the time it takes the earth to make a complete revolution we call a year you have seen in just a few minutes what it took man thousands of years to learn but there are still many questions about the earth and the stars that remain unanswered answering these questions is the challenge of the future by the way since you've been watching this film our earth in its journey around the Sun has travelled 11,000 miles [Music]