Ch. 26.2 Movement of the EarthMARQUES – NOTES EARTH SPACE SCIENCE

Earth’s Motion…2 types – rotation & revolutionRotation – spinning on it’s axis (slightly tilted

compared to its orbit)Spins every 24 hoursEvidence of rotation = days & nights; constellation

movement seen at night; Coriolis Effect; & Foucault’s pendulum.

*Foucault’s Pendulum: a pendulum swings in a straight line, back and forth. A big, heavy pendulum swings all day, but its path seems to move (b/c ground under it is moving).

Revolving Earth…Revolution – the motion of Earth

traveling around the sun 365 ¼ days to complete = to ONE yearEvery FOUR years = Leap year (due to 4 – ¼ adding

up) Earth moves at 29.8 km/s or about 67,000 mph.Evidence:

motion of constellations during yearSeasons (but only combined w/ Earth’s tilt

Revolving Earth Cont…

Earth’s path = elliptical, not circular. Earth point is closest to the Sun at its

perihelion And farthest away at aphelionDifference between the two is not very big.

Aphelion & Perihelion

Notice - Earth is closer to the sun in January, our winter. **This is how we know that the tilt causes the seasons, not the distance.

Calendars: Ancient civilizations followed sun’s motion and moon to predict seasons. They had some type of calendar

Months - roughly based on the 29 day revolution of Earth’s moon. Older calendars - based on lunar cycle Cause of some religious holiday’s date

changes

Modern Calendar: Based on the Earth’s revolution around the Sun. Adapted to fit the fact that the Earth’s

rotation does not quite match the revolution: One solar year is 365 ¼ days.

Time Zones

Time Zones: Keeps noon @ highest point of the Sun 24 time zones - one

hour apart – about 15o of longitude.

Follows national and state borders where possible.

• International Date Line: Where the date changes (mid Pacific to avoid land)

Equinox Equinox: moment when sun crosses the celestial equator. Daylight & darkness - equal on all

parts of the world. Vernal Equinox – Mar. 21-22Autumnal Equinox – Sept. 22-23.

Solstices: Points where the sun is as far north or south as possible.

Same as highest / lowest point in the sky.

June 21 or 22nd – summer solstice; Dec. 21 or 22nd – winter solstice.

Arctic & Antarctic Circles: beyond these lines, 24 hour light/darkness at Solstice.

Why do we change the time??

Daylight Savings Time: Days = longer in the summer. In WWI, to save fuel by not using lamps in the evenings,

people started setting clocks ahead in summer months.

Seasons: Caused by the tilt of the Earth’s axis compared to its orbit (23.5 o) In winter, sunlight hits at an angle, spreads out

further, and is less bright. In summer, more direct sunlight and longer

days keep us warmer.