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Planetary Motion
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Gravity
Key Concepts:
Terms in this set (22)
Kepler's 1st Law
States planets orbit in an ellipse with the Sun at one foci
Kepler's 2nd Law
States planets sweep out a triangle in their orbit that is equal in area to another triangle over the same period of time.
Kepler's 3rd Law
States the period of a planets orbit "squared" is equal to its distance to the sun "cubed".
Western Elongation
Occurs at sunrise to the east, where Mercury is at its greatest separation from the Sun from Earth's perspective.
Eastern Elongation
Occurs at sunset to the west, where Mercury is at its greatest separation from the Sun from Earth' perspective.
Ellipse
Oval shape of a planet's or comet's orbit, where the radius (distance to Sun) varies throughout its path.
Circle
An ellipse where both foci are at the same spot, or "c" equals zero.
Eccentricity definition
ratio measuring the degree to which an ellipse is stretched. calculation .
Low eccentricity
Describes a planet's orbit. E=.02
High eccentricity
Describes a comets' orbit. E=.92
Period
Time it takes a planet to make one revolution around the sun. This term squared is equal to it's distance cubed.
Distance
The radius measured to the Sun in AU's. Changes as you orbit around the Sun.
AU
"astronomical unit". Distance measurement used in the solar system (earth = 1)
Aphelion
A planets furthest distance to the Sun.
Perihelion
A planets closest distance to the Sun.
Major Axis
Line that runs through both foci of an ellipse. Is longest distance across, and is equal to 2 X "a".
Minor Axis
Line that cuts the Major axis in half creating two semi-major axis's.
Semi major Axis
Major axis divided by 2. Is also labeled as "a".
Foci
Two points used to draw an ellipse, where increasing the distance between the two make it more eccentric.
"a"
is equal to Major axis divided by 2.
"c"
distance from one foci to the semi major axis.
Formula for calculating eccentricity
c/a
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