
Earth’s position in space
◦ Not the center of the Solar System
◦ Elliptical orbit
◦ Plane of the ecliptic

Shape & Size of Earth
◦ Oblate spheroid

Motions of Earth
◦ Revolution
 Year
◦ Rotation
 Day
◦ Precession
 Epoch

Revolution
◦ Our movement around the Sun
 Counter-clockwise
◦ 93,000,000 mi. away
◦ 66,000 mi./hr. (average)
 Faster in winter, slower in summer
 Kepler’s 2nd Law
◦ 365.25 days to complete
 How do we mark this time?
 Sidereal year
Kepler’s 2nd Law
The orbital speed of a planet varies so that a
line joining the Sun and the planet will sweep
over equal area in equal time intervals.

1mo.
1 mo.

Key variables in the causes of seasons
◦ Tilt of the Earth’s axis
 23.5 degrees
◦ Location of the Earth in its orbit

Latitudes as it Relates to the Sun
◦
◦
◦
◦
◦

Equator – 0 degrees
Tropic of Cancer – 23.5 degrees N
Tropic of Capricorn – 23.5 degrees S
Arctic Circle – 66.5 degrees N
Antarctic Circle – 66.5 degrees S
An Analemma
 Seasons
◦ 2 solstice
 Solstice = “Sun stand still”
 June 21 or 22 –Summer Solstice
 December 22 or 23 – Winter
Solstice

Sun’s position in the sky
◦ Summer Solstice
 Rise - NE
 Noon
 Set – NW
 Length of the day
◦ Winter Solstice
 Rise – SE
 Noon
 Set – SW
 Length of Day

Seasons
◦ 2 equinox
 Equinox = equal (day & night hrs.)
 March 21 – Spring Equinox
 September 21 – Fall Equinox
 Sun’s position in the sky
 Rise – directly east
 Noon
 Set – directly west
 Length of the day

Rotation
◦ East to west direction (here on Earth)
 Also west to east (viewed from space)
 23:56:04
 15 degrees/hr.
◦ Foucault pendulum

Precession
◦ 26,000 yr. cycle
◦ Significance of the North Star

A system of coordinates
◦ Latitude
 Parallels
 Measures N & S
 Runs E & W
 Equator
◦ Longitude
 Meridians (long lines)
 Measures E & W
 Runs N & S
 Prime Meridian
 Greenwich, England


Latitude & Longitude of St. Joseph, MO
◦ 39 degrees 45 minutes 29.94559 seconds N
◦ 94 degrees 47 minutes 6.49119 seconds W
Latitude & Longitude of Kansas City, MO
◦ 39 degrees 06 minutes 34 seconds N
◦ 94 degrees 35 minutes 18 seconds W
 Measuring
Time
◦ AM – ante meridian
◦ PM – Post meridian
◦ Midnight
◦ Noon
◦ Solar day – 24:00:00
◦ Sidereal day – 23:56:04

The Moon
◦ Rotation & Revolution
 Synchronous
 Same side always faces toward the Earth
◦ Phases
 New
 Waxing Crescent
 Illuminated area is increasing
 1st quarter
 Waxing Gibbous
 Illuminated area is increasing




Full
Wanning Gibbous
Last quarter
Wanning Crescent
◦ Eclipses
 Solar (New Moon)
 Moon is between Earth & Sun
 Umbra
 Penumbra
 Fig. 16.32
 Lunar (Full Moon)
 Earth is between Sun & Moon
 Eclipses do not happen every month
 Moon’s orbit is inclined 5 degrees