1. Unit 2 Earth in space

5. 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

6. 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

7. 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.
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8. 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:
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9. 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

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11. Precession

12. 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

13. 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)

14. (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)