Concept 3: Longitude and earth’s
rotation
http://www.educypedia.be/education/spacejavaearth.htm
I. Rotation is the spinning of an object on
its axis (imaginary line through the poles
and center). Our axis is from the north
pole through the south pole.
1. Earth rotates at a rate of 360o in 24
hours, or 15o/hr.
2. Rotation gives us our daily clock time
and day and night.
 3.
The earth's true rotation makes the sun
appear to move. This is called the sun's
apparent motion. (How fast does the sun
appear to move each day? The stars? The
moon?)
 4. The sun appears to make an arc
through the sky at 15o/hr.
 5.
Because the earth really rotates from
west to east, or counterclockwise, an
observer (person standing in one spot on
earth) anywhere on earth will see sunrise
(sun appears over horizon in morning)
towards the east and the sunset
(disappear below the horizon in evening)
towards the west.
 6.
Where the sun is during the rest of the
day depends on the observer's latitude
 7. For New York State, the sun is always in
our southern sky during the day.
 8. At
solar noon we say the sun has
reached its highest point of the day. In
New York State, the sun is never ever
ever directly over our heads. (In other
words, the sun is never at zenith in New
York State).
 9.
Evidence of rotation:

a. Coriolis Effect is the deflection of
wind and water from straight line motion.
If the earth did not rotate, winds and water
would not curve, they’d go in a straight
line.

http://www.classzone.com/books/earth_science/terc/content/visualizations/es190
4/es1904page01.cfm?chapter_no=visualization
 b.
Foucault Pendulum appears to change
direction in a circle during 24 hours.
However, the pendulum is actually going in
a straight line, it is the room that is rotating
around it!!!

http://en.wikipedia.org/wiki/File:Pendule_de_Foucault.jpg
 c.
Circumpolar constellations (always
above the horizon) move around Polaris
during the night, giving the suggestion that
we rotate.

http://astro.unl.edu/classaction/loader.html?filename=animations/ancientastro/dipperclock.swf&mo
vieid=dipperclock&width=850&height=340&version=6.0.0
Concept 3: Latitude, seasons
and revolution
 1.
Revolution is an object moving
continuously around another object due to
gravity.
 Earth is a satellite (object revolving
around another object) of the sun.

http://astro.unl.edu/classaction/loader.html?filename=animations/renaissance/configurationssimul
ator.swf&movieid=configurationssimulator&width=850&height=680&version=6.0.0
classaction, planetary motion
from

Our orbit (path around the sun) takes us
one year or 365.25 days (creating leap
year) at a rate of earth’s orbit is 3600/365
days, or 1 0 /day. Think: if our orbital
radius is 92 million miles, how fast, in
miles/day, is our orbit? C=2r.) Slide 24
3. Ancient proofs of earth's
revolution:
 a.
Seasons (change in weather in a cyclic
fashion).
 The size of the sun changes during the
year. We are CLOSER to the sun in
WINTER.
Parallax of stars:

closer stars seem to shift position relative
to farther stars during the year.


Seasonal constellations: the
constellations we see in fall are different
than those we see in winter, spring, etc.
The change is cyclic
http://phys23p.sl.psu.edu/phys_anim/astro/embederQ4.10060.html earth orbit
and seasonal stars
Models of the Solar System (and universe)
http://astro.unl.edu/naap/ssm/ssm.html


Geocentric Model: earth-centered.
Heliocentric Model: suncentered.(Copernican model)

retrograde motion and the ptolemic and
Copernican explanations
http://alpha.lasalle.edu/~smithsc/Astronomy/retrograd.html

ptolemic retrograde
http://phys23p.sl.psu.edu/phys_anim/astro/embederQ4.20100.html

copernican retrograde
http://phys23p.sl.psu.edu/phys_anim/astro/embederQ4.20300.html
4. Causes of Seasons;
a. Tilt of axis: our axis is tilted, with reference
to the sun's rays, at an angle of 23.5o (look
at any globe)

http://astro.unl.edu/classaction/loader.html?filename=animations/coordsmotion/obliquity.swf&m
ovieid=obliquity&width=600&height=400&version=6.0.0

b. Parallelism of the axis: our North
Pole always points toward Polaris. (see
wall chart)
c. Revolution: We orbit the sun on a tilted planet, causing
different parts of the earth to have more light seasonally.
http://astro.unl.edu/classaction/loader.html?filename=animations/coordsmotion/eclipticsimulator.swf&movieid=eclipticsi
mulator&width=970&height=710&version=6.0.0
5. Important dates:
 Equinoxes:
“equal night”. Sun is
overhead at equator. September 22 and
March 21
 Solstice: ‘sun stop’. Sun is either at
Tropic of Capricorn (winter begins
December 21) or Tropic of Cancer
(summer begins June 21).
 Each day, the sun seems to move a little
bit between 23.5 North and 23.5 South
 Actual
position of sunrise changes with
seasons, but is always east
 Position of sunset changes with seasons,
but is always west.




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



http://alpha.lasalle.edu/~smithsc/Astronomy/retrograd.html retrograde motion and the
ptolemic and Copernican explanations
http://phys23p.sl.psu.edu/phys_anim/astro/embederQ4.20100.html ptolemic
retrograde
http://phys23p.sl.psu.edu/phys_anim/astro/embederQ4.20300.html copernican
retrograde
http://astro.unl.edu/classaction/loader.html?filename=animations/renaissance/configu
rationssimulator.swf&movieid=configurationssimulator&width=850&height=680&versi
on=6.0.0 from classaction, planetary motion
http://astro.unl.edu/classaction/loader.html?filename=animations/renaissance/ptolem
aic.swf&movieid=ptolemaic&width=900&height=660&version=6.0.0 ptolemic phases
of venus
http://astro.unl.edu/classaction/loader.html?filename=animations/renaissance/retrogra
de.swf&movieid=retrograde&width=700&height=600&version=6.0.0 retrograde
animation
http://phys23p.sl.psu.edu/phys_anim/astro/indexer_astro.html physics animations
http://phys23p.sl.psu.edu/phys_anim/astro/embederQ4.10060.html earth orbit and
seasonal stars

C= 2 x 92 million x 3.14 = 580 million miles orbit
 Speed of orbit = 580 million miles / 365 days =
1.6 million miles / day
 Hours in a day = 24
 Speed per hour = 1.6 million miles/ day x 1day/
24 hours = 67, 000 mph