Transcript The Earth, Moon, and Sun

The Earth, Moon, and Sun
Orbital Mechanics
Seasonal Changes
Changes in season…..Summer
(June 21)
• Result from the tilt of
the axis of the earth.
• When the earth’s axis
faces the sun, the sun
rays hit most directly
over our northern
hemisphere and we get
the most intense and
longest duration of
sunlight.(Insolation)
Seasons…Fall (Sept 21)
• As the earth continues
its revolution around
the sun, the sun strikes
the earth most directly
over the equator.
• At this time, all earth
locations receive both
hemispheres receive
12 hours of darkness
and 12 hours of light.
Seasons….Winter (Dec 21)
• As the revolution
continues, the earth’s
axis ends up pointing
away from the sun.
• At this time, the
northern hemisphere
receives glancing
insolation resulting in
fewer hours of less
intense sunlight.
The earth’s orbital motion causes the apparent
position of the sun to shift about 1 degree each day
on the celestial sphere.
Orbital motion also results in
phases of the moon….
Orbital motions
Objects remain in orbit because
of…….
• Inertia - objects in
motion tend to stay in
motion in the same
direction and with the
same velocity unless
acted upon by some
outside force (such as
gravity). This keeps
the planet moving in a
straight line into
space.
and gravity...
• which pulls the planet
back into the sun.
• The two forces,
gravity and inertia,
balance one another to
cause planets and
other satellites to
remain in orbit around
the sun or planet.
“Laws” of orbits
• All satellites orbit
around their primaries
(like the earth around
the sun) in elliptical
orbits.
• Ellipses have two
“centers” called foci.
The law of equal area...
• states that a line
connecting a planet to
the sun sweeps out an
area in such a manner
that equal areas are
swept out in equal
times. Thus, the earth
is moving more slowly
when it is farthest
away from the sun.
In order for out space shuttle to go into
orbit, the 2 forces of inertia and gravity
must be in balance.