The Sun-Earth-Moon System 28.3

Earth’s Rotation Ecliptic – the plane in which Earth orbits the sun 2 ways to demonstrate the Earth’s rotation A pendulum The fact that flowing air and water divert from a North south direction to an east west direction – Coriolis effect The length of a day is a little longer than the time it takes for Earth to rotate once on its axis -as it rotates, it moves along in its orbit and has to turn a little farther Solar day – the time period from one sunrise or sunset to the next

Effects of Earth’s Tilt Earth’s axis is tilted toward the sun at 23.5 degrees As earth orbits the sun, the orientation of the axis stays fixed, so at one point the northern hemisphere is tilted toward the sun, and six months later, the northern hemisphere is tipped away from the sun – this causes our seasons

Summer Solstice Summer solstice – sun is at max altitude in the sky in the northern hemisphere around June 21 Sun directly overhead the Tropic of Cancer Daylight hours at its maximum (opposite for Southern Hemisphere) Sun doesn’t set within the arctic circle, and does not rise in the antarctic circle.

Winter solstice Winter solstice – northern hemisphere is tilted away from the sun Sun directly overhead the tropic of capricorn Sun at its lowest altitude in the sky Around December 21 Daylight hours in the northern hemisphere at its minimum Sun never rises in the arctic circle, never sets in the antarctic circle

Equinoxes Earth’s axis is not pointed at the sun – both hemispheres get equal amounts of sunlight Sun is directly overhead at the equator Lengths of day and night are equal for both hemispheres Autumnal equinox Vernal equinox

Phases of the Moon Lunar phases – the changes in the appearance of the moon A result of the movement of the moon around earth The moon does not emit light, we see the moon’s reflection of the sun’s light Waxing gibbous – when we see more than half of the sunlit portion Waxing crescent – when we see less than half of the sunlit portion

Phases of the Moon Between the waxing gibbous and crescent moons, there is a point when we only see half of the sunlit side – this is called first quarter After waxing crescent, the moon continues and is aligned with the sun – we can see the entire sunlit side – this is a full moon

Phases of the moon Waning gibbous – when we see more than half of the sunlit portion Waning crescent – when we see less than half of the sunlit portion Between the waning gibbous and crescent moons, there is a point when we only see half of the sunlit side – this is called third quarter

Lunar month – the amount of time it takes for the Moon to go through a complete cycle of phases Length of a lunar month – 29.5 days, but it takes 27.3 days for the moon to make it completely around Earth once

Tides Tides are an effect of the Moon on Earth, the Earth’s rotation, and the sun The Moon’s gravity pulls on earth and creates bulges of ocean water on the Earth As the Earth rotates, the bulges stay aligned with the moon, so that the ocean level rises and falls ever 12 hours

Tides When the sun and moon are aligned in the same direction, the effects of each combine and the tides are higher – called Spring Tides When the Moon is at a right angle to the Sun, tides are lower than normal – Neap Tides

Solar Eclipses Occurs when the Moon passes directly between the Sun and Earth – blocks our view of the Sun Even though the Sun is much larger than the moon, it’s farther away, so they appear to be the same size When the Moon perfectly blocks the Sun, we only see the outer gaseous layers – total solar eclipse When the Moon blocks only part of the Sun – partial solar eclipse

Effects of Orbits Solar eclipses don’t happen every new moon – the tilt of the moons orbit causes it to not be perfectly aligned The moon moves above and below the plane of the earth and sun The moon’s distance from Earth also changes Perigee – the closest point in Moon’s orbit to Earth Apogee – the farthest point in Moon’s orbit to Earth Moon appears smaller – doesn’t completely block the sun – Annular eclipse

Lunar Eclipses Occurs when the Moon passes through Earth’s shadow Only can happen at the time of a full moon Lunar eclipses occur slightly more than solar eclipses The maximum amount of eclipses sun and lunar that can occur in a year is 7