Earth and Moon Notes

Rotation vs. Revolution Rotation- spinning of earth on its own axis: 24 hours = 1 day = 1 rotation What causes night and day.

Revolution Earth’s movement around the sun is a revolution. One complete revolution = 1 year = 365.25 days.

The Seasons Equator does not experiences difference in temp. and daylight in seasons b/c it receives the most direct sunlight. Poles = extreme temp. differences. Winter in Alaska = 2 hrs of daylight, in summer = sun never sets. Seasons caused by the tilt of the Earths axis – tilted 23.5 degrees

June in Northern Hemisphere Axis tilted towards the sun. Summer – longer days, warmer temperatures NOT caused by the distance from the sun, caused by more direct sunlight.

December in the Northern Hemisphere Earth’s axis pointed away from the sun. Winter = shorter days, colder temperatures, due to less direct sunlight and fewer hours of daylight.

June and December Solstice June 21st = longest day of the year, considered first day of summer. December 21st, shortest day of the year, considered first day of winter.

Equinox in March and September Equinox is halfway between each solstice. Equinox – neither hemisphere is pointed towards or away from the sun. Equinox = equal night = 12 hrs day/12 hrs. night March 21st – spring equinox, September 22nd – fall equinox.

Gravity and Motion Recall that gravity is a force that attracts all objects towards each other. Universal Law of Gravitation – every object in the universe attracts every other object.

Gravity and Motion The strength of gravity is dependent on 2 things: the mass of the objects, and the distance between them. If mass increases, gravity increases. If distance increases, gravity decreases. Weight – the force of gravity on an objects mass.

Inertia and Orbital Motion Two factors keep Earth and the moon in their orbits – inertia and gravity. Earth’s gravity pulls the moon toward it, preventing the moon from traveling in a straight line. The moon keeps moving ahead because of it’s inertia.

Inertia – the tendency of an object to resist a change in motion.

The Moon The positions of the moon, Earth, and sun causes the phases of the moon, eclipses, and tides.

Rotation vs. Revolution A “day” and a “year” are the same length on the moon. One day = 1 rotation of the moon= 29.5 earth days

Dark Side of the Moon The ‘dark side’ is the side we never see. The moons whole set of phases occurs in 29.5 days

Phases of the moon Depends on how much of the sunlit side of the moon faces the Earth

Eclipses occur when…. The moons shadow hits Earth or Earth’s shadow hits the moon There are ‘solar’ eclipses, and ‘lunar’ eclipses

Solar Eclipse Occurs when the moons shadow falls on the Earth. Sun, moon and Earth aligned

Lunar eclipses occur when the earth’s shadow falls on the moon

View of Solar Eclipse

Tides The tides are caused mainly by differences in how much the moon’s gravity pulls on different parts of the Earth

High vs. Low Tide Tides occur in a daily cycle. As the Earth rotates on its axis, any point on Earth goes through a cycle of high tide, low tide, high tide, low tide. The moon’s gravity causes high tide on the side closest to the moon, Low tide occurs when that part of the Earth is at a 90 degree angle to the moon.