Earth In Space Chapter 3 Shape of the Earth Ancient Greeks Earth casts a circular shadow on the moon during a lunar eclipse Shape of the Earth Ancient Greeks Ships were observed to disappear below the horizon as they sailed away from the viewer (276-195 B.C.) Astronomer used geometry to the of the Eratosthenes (276-195 B.C.) Sunlight shone straight down a well at Syene, Egypt June 21 Alexandria is 800 km from Syene Eratosthenes (276-195 B.C.) Measured shadow cast by tall obelisk in Alexandria Calculated angle 7 12 exactly 1/50 of a circle Eratosthenes (276-195 B.C.) If the angle is 1/50 of a circle Then the distance between Alexandria and Syene must be 1/50th the circumference of the Earth
Eratosthenes (276-195 B.C.) 50 x 800 km = 40,000 km Actual distance 40,075 km Earth is an Earth in Motion Rotation ~1000 mph Revolution Moon around Earth 2300 mph Earth around Sun 66,000 mph Earth in Motion Revolution Solar system around Milky Way 230,000 mph Three Main Movements of the Earth on Axis Revolution 1 trip takes days Earth moves at, at. Rotation
The Earth s axis maintains an average incline, or, on its axis. ( ) Axis points the for, then turns for. 3 effects: length of day/night, changing seasons, changing climates with latitude (know this) Full daylight at NP Full darkness at SP Earth s Tilt (KNOW) Full daylight at SP Full darkness at NP Solstices Solstice the sun is at its point has 24 hour light directly overhead of Solstices Solstice the sun is at its point has 24 hour light directly overhead of Equinoxes sun s rays strike the equator almost directly and Earth is illuminated from pole to pole Equinoxes sun s rays strike the equator almost directly and Earth is illuminated from pole to pole What causes the seasons? Caused by Earth s
length of time sunlight falls on a particular location angle at which sunlight hits a region determines amount of solar energy Seasons in Northern Hemisphere Wobble on Axis is at 23.5 degrees Wobbles back and forth from 22.1 degrees to 24.5 degrees and back to 22.1 degrees. Caused by of Sun and Moon on. Evidence of Rotation Observation of other planets rotating Rotating planets are oblate spheroids just like earth Jean Bernard Foucault (1851) Slowly turns clockwise demonstrates counter-clockwise of the under the swing of the pendulum Pantheon in Paris Pendulum Swing Changes with Latitude North Pole Complete turn every 24 hours Equator No turn at all Rotational Velocity Different latitudes have different speeds rotational at A point at the equator has to go farther than a point in Alabama, so it must go faster Coriolis Effect
An of the path of an object that moves within a coordinate system Coriolis Effect Objects moving from the equator will be moving east than the ground Appear to be forced east Coriolis Effect Objects moving the will be moving than the east-moving ground Appear to be forced farther Coriolis Effect Northern Hemisphere Objects moving north or south will appear to turn to the right (KNOW) Coriolis Effect Southern Hemisphere Objects moving north or south will appear to turn to the left (KNOW) Identifying Your Location on Earth Parallels East and west running circles parallel to the equator Latitude (parallels running east and west)--know Angular distance from equator to parallel measured in degrees Meridians North and south running arcs that intersect at both poles Longitude (arcs running north and south) - know Angular distance from prime meridian east or west measured in degrees Observatory,
of the world Longitude Every place on Earth is measured east or west from here New Orleans 30 N, 90 W Finding a Location Subdivisions of angular distance 1 = 60 minutes (60 ) one minute = 60 seconds (60 ) Other Points of Reference Tropic of border of the Northern Solstice Tropic of border of the Southern Solstice Other Points of Reference Circle limit of area where sun does on solstice Circle limit of area where sun does on solstice Measuring Time Sun Time and Clock Time What is noon? When the sun crosses the, has occurred Noon Whenever noon occurs at a given location (longitude) A.M. = morning hours before sun crosses meridian P.M. =
afternoon hours after sun crosses meridian time time from the position of the Sun in the sky the shadow of the gnomon on the sundial Caesar Augustus Sundial Rome, Italy Apparent Local Solar Time Changes Nonuniform and fluctuating Reasons Earth moves sometimes faster and sometimes slower in its elliptical orbit around sun Tilt of Earth Apparent Solar Day vs. Sidereal Day Day interval between of the celestial meridian by the Sun Apparent Solar Day vs. Sidereal Day Day interval between of the celestial meridian by a particular time for Earth to rotate on axis (KNOW) sidereal means hrs min sec Why is the Apparent Solar Day? Earth must rotate a little farther to compensate for orbit extra minutes Apparent Solar Day vs Sidereal Day At time 1, the sun and a certain distant star are both overhead. At time 2, the planet has rotated 360 and the distant star is overhead again (1 2 = one sidereal day). But it is not until a little later, at time 3, that the sun is overhead again (1 3 = one solar day). Apparent Solar Day vs Sidereal Day
Apparent Solar Day vs Sidereal Day Standard Time Zones Each longitudinal line has a different measure of time 360 24 longitudinal lines = 15 each Moving = 1 hour Moving = 1 hour International Date Line ( ) Moving day Moving day What is a Year? Year Interval between two consecutive equinoxes 365 days, 5 hours, 48 minutes, and 46 seconds 365.24220 mean solar days What is a Year? year time required for the Earth to move around its orbit so the Sun is again in the same position relative to the stars than tropical year by minutes Fixing the Calendar Calendar Julius Caesar (46 B.C.) days per year 366th day year every fourth year ( year) Year started at Spring Equinox July (after Julius) & August (after Augustus)
Fixing the Calendar Calendar ( ) Pope Gregory XIII (1582) Revised Julian calendar off by 11 minutes 14 seconds per year only century years divisible by 400 are leap years the year 2000 is leap year the year 2100 is not a leap year The Moon The Moon 384,000 km from Earth (238,000 miles) Diameter ~3500 km ~2200 miles Revolution 3680 km/hr ~2300 mi/hr The Moon -colored gravel or boulders compacted together meteorite impacts Density (2.9 g/cm 3 ) The Moon ( ) Smooth -colored lava rock Density (3.3 g/cm 3 ) No atmosphere Temperature -300 degrees F (night) 417 deg F (day) 205 deg F (at poles) The Moon
The Moon is covered with fine, glassy The Moon Moon s period of rotation is to one revolution around the Earth always see same side of moon from Earth (KNOW) days Earth-Moon System Moon is about 1/81 the mass of the Earth Large enough to move center of mass away from center of Earth Slightly wavy path around Sun Act as a system Earth-Moon System Moon is > ¼ Earth s diameter larger in comparison to its planet than any other moon provides just enough light large enough to keep spherical shape Phases of the Moon Results from Sun, Earth, & Moon positions The Rest of the Story Moon Phases The Moon s side is facing the. Not visible except during solar eclipse The Moon is than illuminated by direct sunlight of the Moon s disk that is illuminated is
Quarter the moon is by direct sunlight of moon s disk that is illuminated is than, but not fully, of moon illuminated is Moon on side Earth than, but not fully, of moon illuminated is Quarter of moon is of moon illuminated is Moon is than illuminated of moon illuminated is Eclipses Earth s or Moon s shadow falling on the other body (know this) Uncommon because of 5 incline of Moon to Earth Sun, Moon, and Earth have to be in line Eclipses Any shadow of any body consists of two parts region of outer of Lunar Eclipse Occurs when the Moon passes through some portion of Earth s shadow. (KNOW) CAN ONLY OCCUR AT Lunar Eclipse Types
Penumbral Lunar Eclipse Full moon enters earth s penumbral shadow Moon dims a little Partial Lunar Eclipse Part of the moon is within Earth s umbra Moon is partially shadowed Eclipse Moon is completely shadowed by earth No direct light from sun reaches the moon Varies in color Near black Red Copper orange Lunar Eclipse Why does the moon turn RED??? Lunar Eclipse Moon Light from sun is (bent) by Earth s atmosphere and Lunar Eclipse animation Solar Eclipse Occurs when the Moon passes between the Earth and Sun (KNOW) CAN ONLY HAPPEN AT
Next solar eclipse visible from US: August 21, Annular Solar Eclipse Moon covers center of sun, but not its edges Moon is too far away from Earth Tides and of sea level Greatest range = and moon Least range = moons high tides and low tides daily in a coastal location Tides attracts water and land nearness of moon to Earth makes its gravity twice as effective as Sun s Tides Side moon tide side Earth is pulled away from from the ocean tide tidal trough Other sides 90 degrees away tide Tides tidal range at moon and moon Tides Gravity of Sun and Moon act on Earth All in line Tides tidal range at quarter moons Tides Sun and moon are at right angles of Moon
Tides Greatest Spring Tides Moon is closest to Earth Perigee 28,000 miles closer than Apogee Moon is Full or New Tides Size of Tides also determined by size, shape, and depth of water basin Coastal Regions 3-10 feet Gulf of Mexico 1 foot Lakes and ponds too small Bay of Fundy 50 feet