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

Earth as a Planet

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

Earth as a Planet

Kepler’s 2nd LawThe 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.

Earth as a Planet

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

Earth as a Planet

Seasons◦2 solstice Solstice = “Sun stand still”

June 21 or 22 –Summer Solstice December 22 or 23 – Winter Solstice

The Earth as a Planet

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

The Earth as a Planet

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

The Earth as a Planet

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

Earth as a Planet

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

The Earth as a Planet

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

The Earth as a Planet

Measuring Time◦AM – ante meridian◦PM – Post meridian◦Midnight◦Noon◦Solar day – 24:00:00◦Sidereal day – 23:56:04

Earth as a Planet

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

Earth as a Planet

◦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

Earth as a Planet