Transcript Earth Sun Moon System

Vocabulary
 Rotation
 Lunar eclipse
 Revolution
 Nutation –will cover
 Precession
 Barycenter-will cover
 Perihelion
 Elliopsoidal Model-will
 Aphelion
 Perigee
 Apogee
 Phases of the Moon
 Solar eclipse
cover
Revolution
 Period of REVOLUTION= one complete elliptical
orbit around the sun or planet (moon).
 Earth=364.26 Why do we need a leap year?
 Mercury=88 days
 Pluto=248 Earth years
 Planets revolve in a counterclockwise direction
around the sun.
Rotation
 The period of ROTATION= movement of planet
around its axis.=1 day/night cycle.
 Earth=24 hours
 Mercury=59 Earth days
 Pluto=6 Earth days
Tilt
 The Earth is tilted on a 23.5 o angle on it’s axis
 http://www.josleys.com/show_gallery.php?galid=313
 The tilt of Earth is the reason day and night are not 12
hours each and why we have seasons.
 The side of the planet tilted towards the sun, is
receiving more direct sunlight and longer
days=summer.
 The side of the planet tilted away from the sun, is
receiving less direct sunlight and shorter days=winter.
Tilt
 http://www.learner.org/jnorth/tm/ReasonsBack.html
 Any planet that is tilted on its axis will have seasons.
 Seasons are marked by specific dates:
 Summer solstice June20/21 –sun is at highest point in
the sky and longest day of the year.
 Winter solstice Dec.21/22-the Northern hemisphere is at
full tilt away from the sun and shortest day of the year.
 Autumnal equinox Sept. 22/23-day and night are equal
 Vernal equnox March 20/21 day-day and night are equal.
Precession
 Change in the direction of the axis but there is not
change in the 23.5o tilt.
 Changes the stars near the pole-Polaris (current) or
Vega.
 Does not affect seasons.
Barycenter
 http://spaceplace.nasa.gov/barycenter/
 The balance between the masses of the planets as they
orbit.
 In the case of the moon and the Earth-the moon doesn’t
orbit the Earth’s exact center, but a point 1,710 km below
the surface. This is where the masses balance each
other.
 Causes the sun to wobble-it is not stationary in the solar
system. As planets tug on it with their gravity it
wobbles, but never goes far from its barycenter.
Nutation
 A wobble around the Earth’s axis 1/2o change/18 year
period.
 Due to the moon and tides.
Ellipsoid Earth
 The Earth’s diameter is wider at the equator than at the
poles-not a perfect sphere.
 Caused by the rotation of the Earth and the centrifugal
force perpindicular to it.
 The earth has a molten core, tectonic plates, and a thin
crust that can move; therefore there is a slight
flattening.
Phases of the Moon
 Oreo activity
 The amount of the moon lit up by the sun.
 ½ of the moon is lit at all times. The amoutn visible
depends on the location of the moon with respect to
the sun and Earth.
 The same side of the moon faces the Earth because its
period of rotation about its axis and its revolution
around the Earth are about the same.
The speed of light is 299,792,458 m/s. The moon is
348,403,000 m away. The hope is that one day space
ships will be able to travel near the speed of light. If
we were travelling to the moon at the speed of light
how long would it take to get to the moon?
2. If the moon revolution speed was half as fast as it is
now, how long would it be between full moons?
3. It is the year 3000 and we are interested in starting a
colony on the moon. The moon has no atmosphere
and plants require oxygen and carbon dioxide to
grow. What could be done to allow plants to grow?
There would be periods of no sunlight. How long
would those periods be?
4. What affects on Earth would we have if we had no
moon?
1.
Eclipses
 Solar eclipse-when the moon moved between the
Earth and the sun.
 New moon phases
 Lunar eclipse-the moon is eclipsed when it moves it
moves within the Earth’s shadow.
 Full moon phases
Solar eclipse
Lunar eclipse
Why don’t we always see
them?
 Moon’s orbit is inclined 5% so most of the phases its
shadow misses Earth.
 Must cross the plane of ecliptic for an eclipse to take
place.