Transcript Celestial Motions

Celestial Objects and Motions
What keeps objects in orbit?
the force that
attracts a body toward the
center of any other
physical body having mass.
Gravity -
Inertia
Dynamic equilibrium
property of matter by
which it continues in its
uniform motion in a straight line
PLANETARY MOTION Models
1. Geocentric Model (Aristotle) –
earth centered
Geo = Earth
Did not
explain
retrograde
motions of
some planets
PLANETARY MOTION Models
2. Heliocentric (Copernicus) –
Sun centered
Helio = Sun
Everything
revolves around
the sun
Motions of Celestial Objects
1. The celestial sphere
describes the dome of
sky that you can
observe
• Celestial objects are
observable objects
like stars, planets,
etc.
Motions of Celestial Objects
2. An arc is the motion
that a celestial object
moves across the sky
3. Polaris does not
appear to move,
therefore has no arc
a. The closer an object is
to Polaris the smaller
is the arc
Starry Night
Motions of Celestial Objects
The celestial objects that arc across the sky
appear to rise in the East and set in the West
b. Except for celestial objects close to Polaris
which appear to revolve around Polaris
c. Also except for the planets which appear
to “wander”, sometimes moving East to
West, sometimes moving West to East,
and sometimes appearing to stand still
= Retrograde Motion
Retrograde Motion
• “apparent” motion that objects are moving
backwards
• Farther from the sun because orbital
velocities are slower
• http://ed.ted.com/on/WAdUQ3Z3
• http://www.youtube.com/watch?v=72FrZz_
zJFU
Apparent Motion of Celestial Objects at the
North Pole and Equator
90o N
0o - equator
Earth’s axis
Motions of Celestial Objects
• All celestial
objects,
including our
moon and sun,
appear to move
15o/hr
• If an arc was
60o long, how
many hours of
time is that?
Apparent Motion of Celestial
Objects at our Latitude
Earth’s axis
of Rotation
Our latitude – 42o N
ROTATION
• Spinning of an object on it’s axis
Earth spins counterclockwise looking down on North Pole
Evidence of Earth’s Rotation
1. Star Trails –
If took a picture with
the aperture open, you
would get a 15o arc of
the star “moving”
- Stars appear to mover
15o/hr around Polaris
• http://www.youtube.com/watch?v=awLEp-R4sA
• http://www.youtube.com/watch?v=fiQxCRqw64
• http://apod.nasa.gov/apod/ap060915.html
2. Foucault Pendulum
• As the Earth rotates under the pendulum, the
pendulum appears to gradually shift the direction
of swing.
• http://www.youtube.com/watch?v=XJc1dn
bVK_0
• http://www.google.com/doodles/leonfoucaults-194th-birthday
3. Coriolis effect
• Causes of winds and oceans currents to
be deflected to the right in the northern
hemisphere and to the left in the southern
hemisphere.
• http://www.youtube.com/watch?v=mcPs_
OdQOYU
4. Day and Night
• If Earth did not rotate, there would be no
evidence shown above!!
Revolution
• Movement around an object
Counterclockwise (CCW)
• Earth revolves _____________
around the sun
Evidence
1. Changing Constellations - Seasonal
changes in apparent positions of
constellations
2. Seasons
The constellations we see change
throughout the year
WHY???
Big Dipper Revolving Around
Polaris in 24 hours
• http://www.onr.navy.mil/Focus/spacescienc
es/observingsky/constellations3.htm
http://ecuip.lib.uchicago.edu/diglib/science/cultural_astronomy/inter
actives/polaris/polaris.swf