The orbit of the Earth

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The orbit of the Earth Equation of an ellipse or
circle x2/a2 y2/b2 1 An elliptical orbit is
said to be a closed orbit for a planet or a
comet. a semi major axis, b semi minor axis
(see next page) If a b, then you have a circle.
If not, then you have an ellipse. e
eccentricity tells you how circular or flat the
ellipse. b a v 1 e2 where 0 e lt 1 so if
e 0, then b a so you have a circle Think of
e 0 as meaning no flattening. If e 0.8, then
b a(0.6), so b is 60 the length of a and you
get an obvious ellipse.
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Minor axis is vertical
a
Major axis is horizontal
b
Each has a semi axis which is half the total.
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e for Mercury 0.2056, e for Pluto 0.2446 e
for all of the other planets is lt 0.1 This fact
shows how the planetary orbits are very close to
circles even though some diagrams exaggerate
their ellipticness. (I made up this word) e
for Mars 0.0934 These values vary over long
periods of time due to changes in gravity,
because celestial bodies are always changing
position. The Earth to Sun distance varies
between about 147-152 million kilometers. This
does not cause the seasons!
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• Problem find the eccentricity of da Oirth
• given a 149,597,887.5 km
• And b 149,576,999.826 km
• b a v 1 e2 so e v 1-(b/a)2
• Answer e 0.0167

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The orbit of the Moon F.Y.I The word month
comes from the word Moon e Moon 0.055 and the
Moons orbit is counter to the revolution of the
Earth The Moon experiences synchronous rotation,
which means P rotation P sidereal. This is why
we always see the same side of Moon and listen to
Pink Floyd. (Most large moons experience
synchronous rotation) The phases of the moon are
cause by the varying positions of the Earth,
Moon, and the Sun.
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http//www.sirtf.nau.edu/koerner/ast180/lectures/
pic/cdrom/animations/movie-05-06.swf
http//www.sirtf.nau.edu/koerner/ast180/lectures/
pic/cdrom/animations/movie-05-06.swf
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Sun
E
If Earth goes around clockwise in this diagram,
then the moon goes around the Earth
counterclockwise.
5 degrees angle with ecliptic
Sun
E
Moons plane of orbit is 5 degrees off the
ecliptic
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http//www.utdallas.edu/pca015000/ISNS_4371/slide
s/phases_of_the_moon.swf
http//www.utdallas.edu/pca015000/ISNS_4371/slide
s/phases_of_the_moon.swf
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The Terminator - An imaginary line on the moon
that separates the dark portion from the
illuminated portion. Its location depends on the
phase Waxing - to grow larger Phases between
new and full are waxing
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Waning -Means to grow smaller Phases between
full and new SYZYGY (I like this word) When
sun, moon and earth are lined up Occurs during
new or full moon
Quadrature When moon is at right angle to
sun Occurs during 1st or last quarter
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Libration (not libation)
We actually see a bit more than the same side of
the Moon
The moon revolves faster when it is closer to the
Earth and slower when it is farther away.
But, the moons rotation rate stays constant
(excluding very very slight changes), So this
results in something called librations.
Check out this link http//www3.telus.net/public
/aling/lunarcal/Help/190.htm http//www3.telus.ne
t/public/aling/lunarcal/Help/190.htm
This means that we sometimes see more of the
right side of the face of the Moon and sometimes
we see more of the left side of the face of the
Moon. Due to libration, we can see 59 of the
surface of the Moon.
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