The Ecliptic
„
The Sun,
Sun planets,
planets and moons generally
move along the same geometric plane:
The Ecliptic
– Apparent path that the Sun makes in the sky
– Rise in the east & set in the west
– Appearance is due to Rotation of Earth on
axis
– Annual revolution change in altitude & timing
– The Zodiac
Tilt of Earth’s Axis
Controls Sun Angle
Which Determines Area and
Intensity (energy)
Sun Angle
„
Called Angle of Insolation (Incoming
Solar
Sol
ar Radation
Radation))
– Solar rays at 90
90°° are direct, the smaller the
angle
g the less direct and lower the
temperature
Earth’s Axis is tipped
pp 23.5°
23.5° to the Ecliptic
p
„ Only between Tropic of Cancer (23.5°
(23.5° N)
and the Tropic of Capricorn (23.5
(23.5°° S)
receive the direct (vertical) sun
„ As latitude increases
increases, the intensity of
insolation decreases.
„
3 Causes of Seasons
Revolution of Earth around the Sun
„ Tilt of Earth’s axis to 23.5°
23.5°
„ Parallelism
P ll li
off Earth’s
E th’ axis
i = the
th north
th axis
i
(pole) is always pointed towards Polaris
(North
(N th St
Star))
„
Earth’s Motion Around Sun
Counterclockwise revolution
Rotation of Earth
C
Counterclockwise
t l k i turning
t i on
axis
„ Sun rises in east and sets in
west, as does moon and other
planets
„
– What would happen if the Earth did
not rotate
otate on its aaxis?
is?
„
Foucault Pendulum
http://www.youtube.com/watch?v=wlhHWYKswik http://www.youtube.com/watch?v=Ax6Pij
http://www.youtube.com/watch?v=Ax6Pij--CI6c
„
Coriolis Effect –
apparent deflection
of winds (to the wind’s right in No.
Hemisphere) http://www.hulu.com/watch/1924/the
http://www.hulu.com/watch/1924/the--simpsonssimpsons-southernsouthern-
hemisphere http://upload.wikimedia.org/wikipedia/commons/b/b6/Corioliskraftanimation.gif
Geocentric Model of the World
„
Ptolemy 140 AD
– Geometric model to
predict the position of
the sun, moon, and
planets
– Uses Epicycles along
a Deferent to explain
retrograde motion
of Mars and Jupiter
p
– No evidence only
“common sense”
Heliocentric Model of the World
„
Copernicus
– 1543 AD “On the
Revolutions of the
Heavenly Bodies”
– Sun centered with planets
in Perfect circles along
ecliptic
– More accurate predictions
with simpler math than
Ptolemaic model
– explained retrograde
motion
Evidence for Heliocentric
„
Galileo 1610
– Phases
Ph
off V
Venus & moons off
Jupiter
„
Kepler 1609
1609--1611
– Orbits elliptical using Brahe data
„
Parallax 1883
– Friedrich Bessel first successful
measurements of stellar parallax
for the star 61 Cygni using a
heliometer..
heliometer
„
Observations from space 1950’s
1950 s
Yearly revolution of Earth around the Sun
Tilt of Rotation axis
Earth-sun
distance
varies
i