Download Earth`s Motions

New observations lead to changes in
scientific theory
• What’s wrong with the image on the
right, which shows Ptolemy’s popular
scientific theory 2000 years ago? This
is called the geocentric model of the
solar system.
• The heliocentric model was proposed
by Copernicus about five hundred
years ago w/better observations
• Galileo Galilei convinced many that
this model was correct after the death
of Copernicus.
Earth’s Motions
• ROTATION = the spinning of an object, such as a planet,
moon, or star, on an imaginary axis like a top
– Earth’s rotation takes 24 hrs
– Daily patterns are caused by rotation
• REVOLUTION = an object’s movement around another
object in a path called an orbit (ex. planet around the Sun)
– Earth’s revolution around the Sun takes 365.25 days (or
one year)
– Yearly patterns are caused by revolution
Rotation (spin on axis = 24 hours)
• Evidence
– Foucault Pendulum = has a steel wire with a bob on
the end that is clamped to allow the pendulum to
swing freely. The amount of observed change in the
pendulum is dependent on latitude (maximum
rotation of 360° in 24 hours at the poles to no
observed effect at the equator).
Foucault Pendulum at the North Pole
Time-lapse Foucault Pendulum
Rotation
(spin on axis = 24 hours)
• Evidence
– Coriolis Effect = Objects traveling over long distances
will be deflected to the right in the Northern
hemisphere and to the left in the Southern
hemisphere (also affects wind and water currents).
• Intended Paths
• Real-life example!
Revolution
(around the Sun = 365.25 days)
• Evidence
– Parallax Effect = The apparent shift in a star’s
position that occurs because Earth has moved in its
orbit. This results in seeing an object from
different angles, changing the perspective.
Astronomers view stars from one side of the Earth’s
orbit and then from the other side in an attempt to
detect parallax.
Revolution
(around the Sun = 365.25 days)
• Evidence
- Seasonal Changes in
Constellations = During the
summer, certain constellations
are visible in the nighttime sky.
During the winter, when the
Earth is on the opposite side of
the Sun, the nighttime sky faces
the opposite side of the
universe, so we see different
constellations.
See both rotation and revolution at work!
Revolution (around the Sun = 365.25 days)
• Evidence
– Retrograde Motion = backwards (west to east) motion
relative to the stars because Earth moves faster than outer
planets. This causes the outer planet to temporarily seem
to move backward in the sky as we pass it. This variation
in motion is how planets were discovered. The retrograde
motion of planets is more easily explained by the
heliocentric model rather than the geocentric model.
The Night Sky
-Celestial objects = Objects observed in the sky during
day or night as observed from Earth
- For the most part, celestial objects appear to move
from east to west in the sky. They rotate
counterclockwise around Polaris (North Star) at about
15o/hour (or 360o in 24 hours). This is because Polaris
is directly above Earth’s axis of rotation so it appears
not to move in night sky.
- This rotation can be seen with star trails,
which are time-lapse photographs of a
certain area of the night sky that maps the
movements of celestial objects. Circumpolar
stars never set below the horizon due to their
proximity to one of the celestial poles.
Therefore, they are visible for the entire night
on every night of the year.
- A constellation is a group of
stars that make an identifiable
pattern in the sky. An asterism is
a smaller grouping of those
stars. Which constellations are
seen each night depends on
where the Earth is in its path
around the Sun.
How many degrees did
the stars move
from diagram 1 to
diagram 2?
30° (2 hours x 15°)
How can you find
Polaris?
It’s the only one that
didn’t move (and the last
star in the handle of the
Little Dipper)
What hemisphere must
you be in? Why?
Northern
because Polaris can only
been seen in the North
What direction must
you be looking?
North
What direction do
the stars appear to
move?
Counterclockwise
What causes the
stars to appear to
move?