ASTRON 100 Lecture Notes - Lecture 3: Jigsaw Puzzle, Solar Time, Distant Star
7 Sep 2016
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Angular size = diameter of object/distance to object: measured in radians, 1 radian = 57. 3 degrees. How do we locate objects on the sky: ncp north celestial pole. Celestial sphere imagine earth is stationary, sphere is revolving around the earth. The only time the sun is in the northern sky in amherst is just after sunrise and just before sunset in the summer. Time is a dimension (a fourth dimension, fundamentally different from other 3) Time is relative (not absolute: two people traveling at different speeds experience the flow of time differently. Time may have a beginning (the big bang - unlike the spatial dimensions) Time has a direction (unlike the spatial dimensions) Physical time direction (stephen hawking, a brief history of time) The three arrows of time: thermodynamic: the direction in which disorder increases, psychological: the direction in which we remember the past and not the future, cosmological: the direction in which the universe expands or contracts.
