Astronomy!!! - Cloudfront.net
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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.