Download Movement of the Planets Shape of the Earth

Natural Science II – ERTH 1040
Movement of the Planets
Shape of the Earth
J. D. Price
Revolution
Orbit – gravitational movement
Revolution is counter clockwise
(from top)
Not constant velocity
Mercury
0.24 years
Pluto
248.6 years
Earth Revolution
ravg = 150 E 6 km (93 E 6 mi) = 1 A.U.
Closest in January
perihelion (- 2.5 E 6 km)
Furthest in July
aphelion (+ 2.5 E 6 km)
Inclined at 23.5o to the ecliptic (orbit) plane
Equinoxes and Solstices – seasonal variation
Shape of the Earth
• What observations do you have?
• Are you able to explain these?
• Could you predict behavior not
observed?
• Are you able to validate your
predictions?
"The facts are simple, the earth is flat…sunrise and sunset are
optical illusions."
Charles K. Johnson
the late president of the International
Flat Earth Research Society.
The cosmos of the Zetetics.
Picture © 1992 by Robert Schadewald
Aristotle's proof
Earth is a sphere
Axis of rotation
More about rotation later…
Revolution – reason for seasons
Please note: axis of rotation is
constant 23.5o throughout the year!
Precession
Result of oblate shape and the moon
Axis wobble with a 26,000 year period
Vega will be the North Star in another 12,000 years
Helical Path
Rotation
Planets need not rotate, but all do
Duration of one rotation
Mercury
58.65 days
Venus
243.01 days (r)
Earth
23 h 56 min 4.1 s
Jupiter
9 h 50.5 min
Mars
24 h 37 min 22.6s
Saturn
10 h 39 min*
Uranus
17 h 14 min (r)
Neptune
16 h 3 min
Pluto
6.39 days (r)
Earth’s moon does not rotate
with respect to the Earth
Questions:
•How do we know the other
planets rotate?
•How do we know the Earth
rotates?
Saturn
2004 Cassini’s observations
10 hr 45 min 45 ± 36 sec.
1980-81 Voyager flybys
10 hr 39 min 24 ± 7 sec
6 minutes slower now Three options
1. Saturn is slowing
2. Voyager or Cassini
measurement is incorrect
3. Decoupling of the
rotation signal
Measuring Rotation on Gaseous Planets
http://www-pw.physics.uiowa.edu/space-audio/
50 to 500 kHz electromagnetic wave called Saturn
Kilometric Radiation (SKR)
Rotation
Photo © F. Giovannangeli
Foucault Pendulum
The earth's rotational velocity
Objects moving north or south pass over the surface
that is rotating at a lesser velocity - deflection in the
object path.
v at poles = 0 km/hr
v at equator = 1,670 km/hr
Hypothetical Spain-Ivory Coast missile exchange
Intended
path
Actual path
French engineermathematician
Gustave-Gaspard
Coriolis
Coriolis Effect
The small force due to the decreasing v in
rotation as one moves north or south from
equator.
Northern hemisphere – right deflection,
counterclockwise
Southern hemisphere – left deflection, clockwise
You can see this air travel, satellite movement, winds
and related weather phenomena, a really specialized
basin-drain system.
You can’t see this the draining of water in average
bathroom fixtures
Size of the Earth
Greek naturalist
Eratosthenes – 250 B.C.
Alexandria
Syene (Aswan)
Highest latitude of direct
sunlight (June 21), Tropic
of Cancer
Copyright © 1998 Oriental Institute, University of
Chicago
http://www-oi.uchicago.edu/OI/INFO/MAP/SITE/
Noon, Summer Solstice
Spherical
Earth
7o / 360o = 1 / 51.4
5,000 stadia between cities
Circumference of the Earth =
257 kstadia
Circumference of the
Earth = 257 kstadia
Great, what’s a stadium?
~185m
842 km between Syene and Alexandria
So Ce = 47,545 km
Actual modern measurement of Ce = 43,278
km – Not bad
Round Earth
The Earth is actually an oblate
spheroid
•de = 12,756 km (7,926 mi)
•dm = 12,714 km (7,900 mi)
•Asymmetrical – North pole is
higher than average surface,
South pole is lower.
Polar Coordinates
Parallels – small circles
& equator
Latitude – arc angle
from equator
Meridians – great circles
Longitude – arc angle
from prime
18-351
Important Latitudes
Please note: 23.5o is the same as 23o 30’
Important Longitude
Prime meridian
http://www.chrysostom.org/andr
ew/
Latitude is a no-brainer: the position of the
sun or a star and days since solstice
Longitude is much trickier.
John Harrison’s H4
Accurate time keeping to a known
solar reference point
First “accurate” seaworthy chronograph
-orDetailed calculations on the
positions of planets and moons
More on time later…
http://rubens.anu.edu.
au/
Movement of Planet Earth
•Rotation at equator = 1,670 km/hr (~1,040 mi/hr)
•Revolution around Earth-Moon gravitational center – 50
km/hr (~30 mi/hr)
•Revolution around Sun – vavg = 106,000 km/hr (~66,000
mi/hr)
•Solar system movement around Milky Way core = 370,000
km/hr (~230,000 mi/hr)
•Star group movement relative to others = 1,000,000
km/hr (~700,000 mi/hr)
•Galactic movement = 580,000 km/hr (360,000 mi/hr)
•Minor changes in Earth orbit, tilt, time of parihelion.
In terms of absolute motion – all historical locations on
Earth are grossly inaccurate
The Home Planet
•Third planet from the sun
•Fifth in diameter and mass
•First in density
•Strong magnetic field
•Atmosphere rich in oxygen (O), carbon
dioxide (CO2), and nitrogen (N)
•Surface temperatures and pressures
permit liquid H2O.
NASA Clementine
Thoughts?
Where on Earth at apparent local noon, June 21
Northward pointing shadow?
No shadow?
When and during what season are we closest to
the sun?
Why aren’t lunar eclipses a monthly event?
In what phase is the moon if it rises at sunset?