Download Eccentricity

Eccentricity and Elliptical Orbits
All planets revolve around the Sun in
an elliptical orbit. The name of that shape is
an ellipse. An ellipse is an oval shape.
Ellipse
Eccentricity is the measure of how out of round an orbit is.
This means it is a number that represents the shape of an orbit.
The eccentricity # ranges from 0 to 1.
11
The e = 0
The e = 0.5
The e = 0.8
Mrs. Degl
1
e = eccentricity
e=d
L
d = distance between foci
L
L = length of the major axis
f 1 and f 2 are each a
foci. One focus is
always a star. Our
solar system has the
Sun as a focus.
d
f1
f2
Mrs. Degl
2
To draw an ellipse:
1. You must carefully place two push pins in a piece of cardboard.
The push pins must be the proper distance apart. Each push pin
represents one focus. The distance between them is called the
“distance between foci”.
2. Next, you must place your loop of string around both push pins.
3. Last, you must drag your pencil around the inside of the string.
This will create your ellipse.
Mrs. Degl
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Helpful Hints
1. The eccentricity formula is on the front
cover of your ESRT’s.
2. An eccentricity close to the # 1 means that
the orbit is VERY elliptical. It looks like an
oval shape. (The # 1 looks like a straight line, and a
shape like
is almost a straight line.)
3. An eccentricity close to zero means that
the orbit is NOT VERY ECCENTRIC or it
is almost a circle. (Zero looks like a circle )
Mrs. Degl
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