In the Ptolemaic system, the universe is a series of concentric spheres- spheres one inside the other. Earth is fixed, o

8. In the Ptolemaic system, the universe is a series of concentric spheres- spheres one inside the other. Earth is fixed, or motionless, at the center of these spheres.

14. Part 2 -- Copernicus (15 minutes) The Copernican model was based on the hypothesis that the Earth moves, in two ways. {READ}Part 2 -- Copernicus (15 minutes) The Copernican model was based on the hypothesis that the Earth moves, in two ways. {READ}

15. Copernicus believed that the Earth rotates once per day, and revolves around the Sun once per year, as shown in the figure. Do you think these motions of the Earth affect you? Well, they produce day and night; and they produce the seasons. {READ reasons for seasons} The axis of rotation of the Earth is constant (points always in the same direction) and is at an angle to the plane of the orbit. Therefore the solar illumination in the northern or southern hemisphere varies throughout the year as the Earth goes around the sun. Solar illumination is greatest during the summer and least during the winter. A common misconception is that the Earth is closer to the sun during the summer (so that the summer is hotter). That�s false! The distance to the sun has nothing to do with the seasons. Perihelion occurs in December. In any case, summer in the northern hemisphere is winter in the southern hemisphere; and vice versa. If the distance to the sun were relevant, then the two hemispheres would have the same seasons. But, on the contrary, their seasons are out of phase by 6 months. Right now � today -- it is winter in Australia and South America. The figure shows the solstices and equinoxes (A, B, C, D). At winter solstice (for the N hemisphere) the axis of rotation points away from the sun, so that the N hemisphere gets the least solar radiation. At summer solstice (for the N hemisphere) the axis points toward the sun, so that the N hemisphere gets the most solar radiation. Copernicus believed that the Earth rotates once per day, and revolves around the Sun once per year, as shown in the figure. Do you think these motions of the Earth affect you? Well, they produce day and night; and they produce the seasons. {READ reasons for seasons} The axis of rotation of the Earth is constant (points always in the same direction) and is at an angle to the plane of the orbit. Therefore the solar illumination in the northern or southern hemisphere varies throughout the year as the Earth goes around the sun. Solar illumination is greatest during the summer and least during the winter. A common misconception is that the Earth is closer to the sun during the summer (so that the summer is hotter). That�s false! The distance to the sun has nothing to do with the seasons. Perihelion occurs in December. In any case, summer in the northern hemisphere is winter in the southern hemisphere; and vice versa. If the distance to the sun were relevant, then the two hemispheres would have the same seasons. But, on the contrary, their seasons are out of phase by 6 months. Right now � today -- it is winter in Australia and South America. The figure shows the solstices and equinoxes (A, B, C, D). At winter solstice (for the N hemisphere) the axis of rotation points away from the sun, so that the N hemisphere gets the least solar radiation. At summer solstice (for the N hemisphere) the axis points toward the sun, so that the N hemisphere gets the most solar radiation.

17. Anti-Copernican Attacks The Bible: Joshua commanded the earth to stand still The Earth: too massive to move! Motion: why don�t objects spin off? Moon: how can the moon orbit the earth and the sun at once?