Revolution: Earth’s orbit around the Sun
Orbit – path of motion around the Sun
Ellipse – (oval) the curved shape of a planet’s
Orbit
Eccentricity – the flattening of an ellipse or how
out of round it is (noncircular)
Formula: Ecc = distance between foci
Length of the major axis
The Sun is at one of the
Foci for All of the planet’s
orbits
Perihelion – when the Earth is closest to the Sun
(January 4th)
Aphelion – when the Earth is farthest from the
Sun (July 4th)
** These are based on the apparent diameter!
Orbital speed – how fast the planet travels in
its orbit around the Sun, depends on distance
from the Sun
 perihelion – closest, most gravitation,
most KE, least PE, fastest in orbit
 aphelion – farthest, least gravitation,
most PE, least KE, slowest in orbit
KE = kinetic energy = energy of motion
PE = potential energy = stored energy
(resting)
Gravitation – the attractive force that occurs
between any 2 objects in the Universe
: depend on mass(size) and distance
**the larger the objects (planets) and the
closer they are, the more gravitation
F = m1m2
Distance squared
Tides are stronger when the Sun – Earth – Moon
are all aligned
Kepler’s Laws of Planetary Motion
1. planets travel in elliptical orbits
2. equal area law - a line connecting Earth to the
Sun would pass over equal areas of space in equal
time: Because the Earth’s orbit is elliptical
3. Harmonic Law – the farther a planet is from the
Sun, the longer its period of revolution
Period – amount of time it takes a planet to
complete one orbit around the Sun
Seasons
June 21st – first day of Summer (solstice)
 the Sun is perpendicular at 23.5
degrees North (Tropic of Cancer) at
solar noon
 longest day of the year
 16 hours of daylight, 8 hours of
darkness
 Sun will rise North of East, move
across the Southern sky, and sets
North of West
 Northern Hemisphere tilted toward
the Sun
September 23rd – first day of fall/ autumn,
 (Autumnal Equinox)
 the Sun is perpendicular at 0
degrees (Equator)
 12 hours of daylight and darkness
 Sun will rise due East, move
across the Southern sky, and set
due West
December 21st – first day of Winter (solstice)
 Sun is perpendicular at 23.5
degrees South, (Tropic of
Capricorn)
 Shortest day of the year
 8 hours of daylight, 16 hours of
darkness
 Sun will rise South of East, move
across the Southern sky, and set
South of West
 Northern Hemisphere tilted away
from the Sun
March 21st – first day of Spring, (Vernal
Equinox)
 Sun is perpendicular to 0 degrees
(Equator)
 12 hours of daylight and darkness
 Sun will rise due East, move
across the Southern sky, and set
due West
(for the Regents) Sunrise is 6:00 am, Sunset is
6:00 pm (unless told otherwise)
Earth rotates 15 degrees per hour
Constellations – group of stars that appear to
make a pattern in the sky
 88 different constellations
 circumpolar constellations appear to
move around Polaris, these depend on
your latitude
 appear to move east to west because the
Earth rotates west to east
 the constellations you see change with the
seasons because of the Earth’s revolution
around the Sun
 Polaris is at the end of the handle of the
Little Dipper (Ursa Minor – Little Bear)
 Closest star to the Sun is 40 trillion km
away – Alpha Centauri
 Retrograde motion – planets appear to
move backward as Earth passes them in
orbit
Rotation
Foucault Pendulum – best evidence of Earth’s
Rotation
Coriolis Effect – winds curve to the right in
the Northern Hemisphere because the
Earth rotates (southern hemisphere)
The Moon
Phases of the Moon – varying amounts of the
moon’s surface that is seen from Earth
 Caused by the Moon’s revolution
around the Earth
 Perigee – nearest (closest) point
 Apogee – farthest point
o Moon’s orbit is elliptical
 5 degree difference in planes of the
Moon and Earth’s orbit causes eclipses,
also why we don’t get the eclipses every
lunar month
 Sun and Moon look equal in size in the
sky because the Sun is 400 times larger
but 400 times farther away
 The Moon will rise 50 minutes later
each day because as the moon revolves
around the Earth, the Earth is revolving
and rotating
 Only one-half of the Moon is lit ALL
the time, it is not Full all the time
because one cannot always see the
whole lighted side
 You always see the same side of the
Moon, because it rotates at the same rate
that it revolves
 A lunar month is 29.5 days. The
moon’s revolution period is 27.3 days.
The reason for the difference is because
as the Moon revolves around the Earth,
the Earth is revolving around the Sun.
Lunar eclipse –
o Sun – Earth – Moon
o Moon must be in Full Moon Phase
o Can be seen by the entire
nighttime half of the Earth
Solar Eclipse –
o Sun – Moon – Earth
o Moon must be in New Moon Phase
o Can be seen in the shadow of the Earth