PH Earth Science The Earth-Moon System
Planet Earth • Earth is the third planet from the Sun. • Earth rotates (spins) on its imaginary axis and revolves (circles) around the sun. • Water occurs as a solid (ice), a liquid, or a gas (water vapor) • Earth has one natural satellite, the moon. - Satellite: Any object that revolves around another object
Earth’s rotation: • Causes day and night • 50% of the earth is always lit by the sun. • One rotation takes ~24 hours (1 day) Earth’s revolution: • Earth revolvesaround, or orbits, the sun. • One revolution takes ~365 days (1 year) - Orbit: the curved path followed by a satellite (Earth is a satellite of the sun.) Why do things orbit other things? GRAVITY!
Earth’s revolution and seasons: • Earth is tilted on its axis 23.5 degrees • This tilt combined with its revolution causes the seasons. Animation of revolution and seasons • Summer occurs when a hemisphere is tilted towards the sun; winter occurs when tilted away • During summer, direct rays from the sun are more concentrated, thus creating more heat energy
Summer Solstice: day that the North Pole points towards the sun; occurs ~ June 21; North Pole experiences 24 hours of daylight • Winter Solstice: day that the North Pole points away from the sun; occurs ~ Dec. 21; North Pole experiences 24 hours of darkness • Vernal and Autumnal Equinox: days when the North Pole is pointed neither towards or away from the sun - most direct rays of the sun are focused at the equator -Spring ~ March 21, Fall ~ September 21
The Moon • Orbits Earth once every 29.5 days and also rotates on its axis once every 29.5 days. This means the same side of the moon always faces Earth. • Has no atmosphere, no water, and no life. • Is ~¼ the diameter of Earth and has ~¼ the gravity of Earth. • Drastic temperature changes between the light (hot) and dark (cold) side - due to the lack of an atmosphere.
The Moon • 50% of the moon is always lit by the sun; it does NOT give off its own light. • The portion of the lit side facing the earth causes the phases of the moon. • The gravity of the moon and sun cause the Earth’s tides - the daily, periodic rise and fall of water level.
One Small Step… • 12 Americans have walked on the moon. • Apollo 11 was the first manned mission to land on the moon. • Neil Armstrong and Buzz Aldrin were the first men to walk on the moon.
Q: If ½ of the moon is always lit by the sun, why do we not always see it? A: Because the lit side does not always face us! click for animation Phases of the Moon
New moon Waxing Crescent First quarter Waxing Gibbous Full moon Waning Gibbous Third Quarter Waning Crescent New moon Phases of the moon It is more important to know what causes the phases than it is to remember all the names!
Solar eclipses occur when the moon blocks sunlight from Earth’s surface. (S m E) animation • Lunar eclipses occur when Earth blocks sunlight from reaching the moon’s surface. (S E m) animation Solar Eclipse August 11, 1999 Soissons, France
One of Jupiter’s moons causing a solar eclipse on Jupiter (notice the shadow).