In 1915, physicist Albert Einstein proposed a new, more comprehensive understanding of how the universe works. He called his new idea the theory of General Relativity. Einstein’s newest theory suggested that space and time are knitted together throughout the universe as a sort of invisible ‘fabric’ that is distorted - dimpled- by massive objects. Einstein named the fabric ‘space-time’ and re-defined gravity as how we feel and interpret the distortion of space-time caused by massive objects. The motion of the planets around the Sun, for example, is caused by the Sun’s mass distorting the surrounding space-time field into the shape of a well.
Try this at home: four people each grab a bed sheet at the corners and pull until the sheet is tightly stretched. Now a fifth person places a heavy ball (at least a basketball, but lighter than a bowling ball) on the sheet. As the ball rolls to the middle of the sheet it distorts the surface as it moves. That distortion of the sheet as it rolls is much like how space-time is distorted by massive objects, like stars. Use a smaller ball to try making an orbit around the bigger ball. The motion of the smaller ball is determined by the distortion caused by the bigger ball. It’s the distortion of space-time in a bed sheet!
But what does Einstein’s theory of General Relativity have to do with eclipses?
In 1919, British astronomer Arthur Eddington understood that the curvature of space-time should also bend light rays, so he figured that a good test of the theory would be to use the curved space-time field around the Sun to bend light from a star cluster positioned just behind the sun. To see that cluster just next to the sun, the adjacent sky would need to be dark. Eddington used the darkened sky of the May 29, 1919 total solar eclipse at the island of Principe, just off the coast of West Africa, to see the cluster. His measurements of the cluster’s position were close enough to Einstein’s predictions to confirm the theory of General Relativity and catapult Einstein to international stardom. Since then, tests of Einstein’s predictions carried out during total solar eclipses have continually confirmed the validity of his theory and existence of the space-time continuum.
Next Time: Where to go and how to view the August 21 eclipse!