Astronomy Earth Science
Johannes Kepler Kepler developed the Laws of Planetary Motion The orbit of every planet is an ellipse. A line joining a planet and the sun sweeps out equal areas during equal intervals of time as the planet travels along its orbit. Longer orbits have longer periods, and the speed of a planet in a larger orbit is lower than in a smaller orbit. D3 = T2 D= distance in AU T= period in years 1 Astronomical Unit = 93 million miles! Distance from the Earth to Sun
Practice Problem Calculate the period of Mercury if it is 0.39 AU away from the Sun. D=0.39 AU T=? D3=T2 0.393 = T2 T = 0.24 years
Practice Problem Calculate the distance Mercury is from the Sun if its period is 0.24 years. D=? T=0.24 years D3=T2 D3 = 0.242 T = 0.39 AU
Galileo Discovered four moons orbiting Jupiter
Galileo Planets are circular disks and not just points of light Venus has phases just like the moon
Galileo The moon’s surface is not smooth
Galileo The Sun has sunspots (areas of the sun with “cooler” temperatures)