1. The Sun-Earth-Moon System
28.3

2. 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

3. 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

5. 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.

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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