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Astronomy!!!
Earth’s Motion
The two main motions of Earth
are rotation and revolution.
Precession is a third and very
slow motion of Earth’s axis.
ROTATION
 Rotation is the turning, or spinning,
of a body on its axis.
Mean Solar Day!
Two measurements for rotation:
1. Mean solar day (synodic day) is
the time interval from one noon to
the next, about 24 hours.
Sidereal Day!
 2. Sidereal day is the time it takes for
Earth to make one complete rotation
(360º) with respect to a star other than
the sun—23 hours, 56 minutes, 4
seconds.
REVOLUTION
Revolution is the motion
of a body, such as a
planet or moon, along a
path around some point in
space.
The earth revolves around the
sun at an average speed of
107,000 km/hour.
The average distance from the
sun is 150 million km.
Perihelion is the time in January
when Earth is closest to the sun
(~147 million km away)
Aphelion is the time in July
when Earth is farthest from the
sun (~152 million km away)
Perihelion occurs about
January 3.
Aphelion occurs about July 4.
The Seasons!
 The earth is located in a plane with
the other planets and moon that
orbit the sun.
 This plane is called the ecliptic.
 The plane of the ecliptic is an imaginary
plane that connects Earth’s orbit with
the sun.
 Because of the inclination of Earth’s
axis to the plane of the ecliptic, Earth
has its yearly cycle of seasons.
The Ecliptic
The Earth has an axis of
rotation that is tilted about
23.5 degrees.
This tilt is what creates the
seasons!
Precession
There is a third movement of
the Earth that is very, very slow.
It is called Precession.
Precession occurs because the
Earth rotates similarly to a top.
Precession traces out a
cone over a period of
26,000 years.
Motions of the Earth–Moon System
  Perigee is the point at which the
moon is closest to Earth.
  Apogee is the point at which the
moon is farthest from Earth.
Phases of the Moon!
 The phases of the moon are the
progression of changes in the moon’s
appearance during the month.
 Lunar phases are a result of the motion
of the moon and the sunlight that is
reflected from its surface.
The phase of the moon you
see depends on how much of
the sunlit side of the moon
faces Earth.
There are two ways to
describe the moon’s
revolution around the Earth.
There are two types of
revolution: synodic and
sidereal.
Lunar Motions
 The synodic month is based on the
cycle of the moon’s phases. It lasts
29.531 days. This month is based on
the moon’s position relative to……
 THE SUN!!!!
This month is based on New
Moon to New Moon.
 The sidereal month is the true period of
the moon’s revolution around Earth. It
lasts 27.322 days. This month is based
on the moon’s position relative to…..
 A fixed star in the celestial sphere!!!
The difference of two days
between the synodic and
sidereal cycles is due to the
Earth–moon system also
moving in an orbit around the
sun.
Moon’s Rotation and Revolution
The moon’s rotation is also
exactly 27.322 days. It
rotates on its own axis.
ECLIPSES!!!
In its orbit, the moon passes
between the sun and the Earth
and then behind the Earth.
This is what forms the eclipses.
 Relative to the Earth-sun plane, the
moon's orbit is slightly inclined by
about 3 degrees.
 Therefore, because the moon and earth
are not in the same plane of the ecliptic,
you do not get an eclipse every month!
Eclipses!
During a new-moon or full-
moon phase, an eclipse
occurs when the moon’s orbit
crosses the plane of the
ecliptic of the sun/earth.
Solar Eclipse
 Occasionally, the exact alignment of
sun, moon and Earth produces a solar
eclipse.
 This happens only when the moon is in
the new-moon phase and its orbit
intersects the Earth-sun plane between
the Earth and the sun.
Solar Eclipse
Solar Eclipse
In a solar eclipse, the moon
blocks out the sun and its
shadow passes over the Earth.
In the same month as a solar
eclipse, when the moon is full, a
lunar eclipse will also occur.
Lunar Eclipse
In a lunar eclipse, the moon
passes through the Earth’s
shadow, which causes its
light to dim.
There is always a full moon on
the night of a lunar eclipse.
You get 2-4 lunar eclipses a
year.
 If the moon passes through the part of
the Earth’s shadow called the umbra, a
partial or total lunar eclipse will occur.
 If the moon passes only through the
penumbra, a penumbral lunar eclipse
will occur. (Hard to see, even with
telescope.)
Penumbral eclipses are hard to
see (not super dramatic).
Umbral eclipses are much easier
to see.
 There are two types of umbral
eclipses:
Partial: (part of the moon passes
through the umbra)
Total: (all of the moon passes
through the umbra)
 All total eclipses start with a
penumbral eclipse, then a partial
eclipse, then a total eclipse, then a
partial eclipse, then a penumbral
eclipse.
 BUT, you can also have a penumbral
(only) or partial (only) eclipse!!!
Total Lunar Eclipse
Penumbral (only) Eclipse
Partial Lunar Eclipse
Total Lunar Eclipse
Total Lunar Eclipse
Partial Lunar Eclipse
Eclipses
The Order of Things!
 Solar Eclipse:
Sun
 Moon  Earth
 Lunar Eclipse:
Sun
 Earth  Moon
Solar or Lunar???
Solar or Lunar?
The Moon!!!!
Lunar Surface
 The surface of the moon is littered with
craters
 A crater is the depression at the
summit of a volcano or a depression
produced by a meteorite impact.
 Most moon craters were produced
by the impact of rapidly moving
debris.
Mare Imbrium
(Sea of Rains)
Kepler
Crater
Copernicus
Crater
Mare Tranquillitatus
(Sea of Tranquility)
Lunar Surface
 The surface of the moon is covered in
regolith.
 The lunar regolith is a thin, gray layer on
the surface of the moon, consisting of loosely
compacted, fragmented material believed to
have been formed by repeated impacts of
meteorites.
Regolith is also known as moon
dust!!!!!
 There are two physical parts of the
moon’s surface: the highlands and
the maria.
 The highlands are made up of
densely pitted, light-colored areas.
Highlands with craters
 The marias are ancient beds of basaltic
lava, originated when asteroids
punctured the lunar surface, letting
magma bleed out.
 The word maria comes from the Latin
word for sea.
 A maria can also have a rille. A rille is
a long channel associated with lunar
maria. A rille looks similar to a valley or
a trench.
How was the Moon formed?
The most widely accepted model for the
origin of the moon is that when the solar
system was forming, a body the size of Mars
impacted Earth.
The resulting debris was ejected into space,
began orbiting around Earth, and eventually
united to form the moon.