1. ASTRONOMY The Sun-Earth-Moon System

2. Section 1: Earth

3. Properties of the Earth
Earth is a sphere – round 3-D object
Rotation – spinning of the Earth on its axis
Axis – imaginary vertical line around which the earth spins
Rotation causes day and night to occur

4. Properties of the Earth
Magnetic Field – movement of material inside Earth’s core, along with Earth’s rotation, generates a magnetic field
Helps protect us from harmful solar radiation by trapping charged particles from the Sun

5. Properties of the Earth
Magnetic Axis – the magnetic axis is set at an angle of 11.5° from the rotational axis
A compass needle points to the magnetic north pole, not the rotational north pole
Declination refers to the difference between magnetic north and geographic north on a map

6. 11.5°

7. What causes changing seasons?
Orbiting the Sun
Revolution – Earth’s yearly orbit around the Sun
Earth’s orbit is not spherical, it is an ellipse – an elongated, closed sphere
The sun in not in the center, but towards one end of the ellipse
Closest: 147 million km away – Jan. 3
Farthest: 152 million km away – July 4

9. What causes changing seasons?
A Tilted Axis
Earth’s axis is tilted 23.5° from the perpendicular
This tilt causes the seasons
The hemisphere tilted toward the sun receives more sunlight than the hemisphere that is tilted away from the sun

10. What causes changing seasons
Radiation from the Sun
Hemisphere tilted toward the sun receives more direct rays from the sun, thus more solar radiation than hemisphere tilted away from the Sun

11. Solstices
Solstice – the day when the Sun reaches its greatest distance north or south of the equator
Northern hemisphere:
Summer solstice – June 21 or 22
Winter solstice – December 21 or 22
Southern hemisphere:
Summer solstice – December 21 or 22
Winter solstice – June 21 or 22
After the summer solstice the days get shorter; after the winter solstice the days get longer (winter solstice nearly the shortest day of the year)

12. Equinox Occurs when the sun is directly above the Earth’s equator
Occurs in the spring (March 20 or 21) and autumn (September 22 or 23)
During an equinox, the daylight hours and nighttime hours are nearly equal all over world

14. Section 2: The Moon – Earth’s Satellite

15. Motions of the Moon Rotation and Revolution
Moon rotates on its axis and revolves around the Earth
The moon’s rotation takes 27.3 days – the same amount of time it takes to revolve once around the Earth
The same side of the moon always faces the earth

16. Phases of the Moon
Moon phases – the different forms that the Moon takes in its appearance from Earth
New Moon – occurs when the Moon is between Earth and the Sun
Dark side faces the Earth
Full Moon – occurs when all of the Moon’s surface facing Earth reflects light

17. Phases of the Moon
Waxing Phases – occurs after a new moon, where you see more of the illuminated half of the moon each night
Waxing crescent – less than half illuminated
1st quarter – right half illuminated
Waxing gibbous (gibbous means “humpbacked”) – more than half illuminated

18. Waxing crescent
1st quarter
Waxing gibbous

19. Phases of the Moon
Waning Phases – occurs after a full moon, where you see less of the illuminated half every night
Waning gibbous – more than half illuminated
3rd Quarter – left half illuminated
Waning crescent – less than half illuminated

20. Waning gibbous
3rd quarter
Waning crescent

21. Third

22. Eclipses
Solar eclipse – occurs when the Moon moves directly between the Sun and Earth, and casts its shadow over part of the earth
The revolution of the Moon causes eclipses – Moon’s shadow falls on the earth
Lunar eclipse – during a full moon, when the Earth’s shadow is cast onto the Moon
Only occur a few times each year

24. Eclipses Eclipses of the Sun Parts of an eclipse:
Umbra – darkest portion of the Moon’s shadow (person standing in umbra is in a full solar eclipse)
Penumbra – lighter shadow on Earth’s surface (person standing in penumbra is in a partial solar eclipse)

26. Eclipses Eclipses of the Moon
Lunar eclipse – when the Earth’s shadow falls on the Moon
Starts when Moon moves into Earth’s penumbra (curved shadow on Moon)
When completely in Earth’s umbra, Moon goes dark – sometimes sunlight bent through Earth’s atmosphere make Moon appear red

30. The Moon’s Surface
Crater – depression in the Moon’s surface cause by meteorites, asteroids and comets striking the surface
After impact, lava from within the Moon filled these craters
Maria – the resulting dark, flat regions on the surface

31. The Moon’s Origins Many different theories:
Moon captured by Earth’s gravity
Material surrounding the Earth condensed to produce the Moon
Earth ejected molten material that became the Moon
The Impact Theory – Mars-sized object collided with earth, ejected material into space and the particles joined together to create the Moon

32. Section 3: Exploring Earth’s Moon

33. Surveying the Moon
Impact Basins – impact crater – depression left by an object striking the Moon
South Pole-Aitken Basin – oldest identifiable impact feature on Moon’s surface
In the shadow most of the time, thought to contain ice deposits