Unit 2 Earth in space

Kepler’s Laws of Planetary Motion First Law: The orbits of the planets are ellipses with the sun at one focus. c Eccentricity e = c/a

Ellipses & Planet Orbits The Sun is at one focus Nothing is located at the other focus Aphelion is the point farthest away from the Sun For an orbit around the Earth, this point is called the apogee Perihelion is the point nearest the Sun For an orbit around the Earth, this point is called the perigee

Kepler’s Laws of Planetary Motion 2. Second Law: A line from the Sun to the planet sweeps out equal areas in equal times, i.e. planets don’t move at constant speed. 1/18/2019

Kepler’s Laws of Planetary Motion 3. Third Law: The squares of the periods of the planets are proportional to the cubes of their semi-major axes: 1/18/2019

Precession gradual shift in the orientation of Earth's axis of rotation Cause: the gravitational forces of the Sun and the Moon, and to a lesser extent other bodies is similar to the precession of a spinning top Effects: the positions of the south and north celestial poles appear to move in circles against the space-fixed backdrop of stars the position of the Earth in its orbit around the Sun at the solstices, equinoxes, or other time defined relative to the seasons, slowly changes

1/18/2019

Precession

Nutation is a rocking, swaying, or nodding motion in the axis of rotation of a largely axially symmetric object happens because of tidal forces that cause the precession of the equinoxes to vary over time so that the speed of precession is not constant

Barycenter refers to the point about which two celestial bodies revolve around Not usual at the center of an object Can be outside of the object (sun and Jupiter)

(a.) Two bodies of similar mass orbiting around a common center of mass, or barycenter. (b.) Two bodies with a difference in mass orbiting around a common barycenter, like the Charon-Pluto system (c.) Two bodies with a major difference in mass orbiting around a common barycenter (similar to the Earth-Moon system) (d.) Two bodies with an extreme difference in mass orbiting around a common barycenter (similar to the Sun-Earth system)