B: Revolution
• 1. Revolution is an object moving
continuously around another object
due to gravity and inertia..
• Earth is a satellite (object
revolving around another object)
of the sun.
http://astro.unl.edu/classaction/loader.html?filename=animations/renaissance/configurati
onssimulator.swf&movieid=configurationssimulator&width=850&height=680&version=
6.0.0from classaction, planetary motion
2. Our orbit (path around the sun)
takes us one year or 365.25 days
(creating leap year).
rate earth’s orbit is 3600/365
days. This is a rate of 1 0 /day.
(Think: if our orbital radius is
92 million miles, how fast, in
miles/day, is our orbit? C=2r.)
C=2r : C = 2 (3.14) 92 million miles
= 578 million miles
Speed = d/t = 578 M miles/365 days
= 1.58 M miles/day
To find miles/hour: 1 day/24 hr * 1.58 M miles/day =
= 0.066 M miles/ hr = 66, 000 miles/ hour (solar system
revolves around Milky Way at rate of 490,000 miles/hour
3. Ancient proofs of earth's
revolution:
a. Seasons (change in weather in
a cyclic fashion).
The size of the sun seems to
change during the year. We are
CLOSER to the sun in our
WINTER.
b. Parallax of stars: closer
stars seem to shift position
relative to farther stars during
the year.
c.
Seasonal constellations:
we face different parts of the
universe and see different
constellations each season.
http://phys23p.sl.psu.edu/phys_anim/astro/embederQ4.10060.html earth orbit and seasonal stars
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&movieid=obliquity&width=600&height
=400&version=6.0.0
b. Parallelism of the axis: our
North Pole always points
toward Polaris.
c. Revolution: We orbit the
sun on a tilted planet.
http://astro.unl.edu/classaction/loader.html?filename=animations/coordsmotion/eclipticsimulator.swf&movieid=eclipticsimulator&wi
dth=970&height=710&version=6.0.0
5. Important dates:
o Equinoxes: “equal night”.
Sun is overhead at equator.
September 22 and March 21
o Solstice: ‘sun stop’. Sun is
either at Tropic of
Capricorn, 23.50S (our
winter begins December 21)
or Tropic of Cancer, 23.50N
(our summer begins June
21).
o Sunrise is always
TOWARDS east.
o Sunset is always
TOWARDS west.
Date
Sun's
Season
vertical rays beginning
September 23
Equator
0o
Tropic of
Capricorn
23.5oS
Equator
0o
Tropic of
Cancer
23.5oN
December 21
March 22
June 21
Fall
Daylight
for NYS
12 hours
Nighttime
for NYS
12 hours
Winter
8-9 hours
15-16
hours
Spring
12 hours
12 hours
Summer
15-16
hours
8-9 hours
6. Models of the Solar System
(and universe)
a. Geocentric Model: earthcentered.
b. Heliocentric Model: suncentered.(Copernican model)
http://alpha.lasalle.edu/~smithsc/Astronomy/retrograd.htmlretrograde motion and the
ptolemic and Copernican explanations
http://phys23p.sl.psu.edu/phys_anim/astro/embederQ4.20100.htmlptolemic retrograde
http://phys23p.sl.psu.edu/phys_anim/astro/embederQ4.20300.htmlcopernican retrograde
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
http://alpha.lasalle.edu/~smithsc/Astronomy/retrograd.htmlretrograde motion and the
ptolemic and Copernican explanations
http://phys23p.sl.psu.edu/phys_anim/astro/embederQ4.20100.htmlptolemic retrograde
http://phys23p.sl.psu.edu/phys_anim/astro/embederQ4.20300.htmlcopernican retrograde
http://astro.unl.edu/classaction/loader.html?filename=animations/renaissance/configurati
onssimulator.swf&movieid=configurationssimulator&width=850&height=680&version=
6.0.0from classaction, planetary motion
http://astro.unl.edu/classaction/loader.html?filename=animations/renaissance/ptolemaic.s
wf&movieid=ptolemaic&width=900&height=660&version=6.0.0ptolemic phases of
venus
http://astro.unl.edu/classaction/loader.html?filename=animations/renaissance/retrograde.s
wf&movieid=retrograde&width=700&height=600&version=6.0.0retrograde 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