1. Warm-up
What causes the seasons on Earth?

2. Astronomy Sun, Earth and the Moon

3. What is Astronomy?
Astronomy is the study of the universe

4. How is time defined?
Year: time required for the Earth to orbit the Sun

5. How is time defined?
Month: division of the year that is based on the orbit of the moon around the Earth

6. How is time defined?
Day: the time required for Earth to rotate once on its axis

7. Light Year-The distance that light travels in one year.

8. Famous Astronomers: Copernicus
Polish
heliocentric model: the earth rotates around the sun.

9. Famous Astronomers: Galilei
Galileo Galilei
Italian
Developed telescope, discovered moon features, experimented

10. Today - Many Different Types of Telescopes
Objects in space emit radiation from all parts of the electromagnetic spectrum
Radio
Infrared
Ultraviolet
X rays
Gamma rays
The Very Large Array Radio Telescope
in New Mexico, US

11. Electromagnetic spectrum

12. Famous Astronomers: Kepler
Johannes Kepler
German
Detailed planetary motion in 3 laws

13. Famous Astronomers: Newton
Sir Isaac Newton
English
Developed laws of gravity and motion

14. Famous Astronomers: Hubble
Edwin Hubble
American
Confirmed existence of galaxies beyond our Milky Way galaxy
Andromeda Galaxy

15. How Do We Know About Space?
Space is explored by humans using telescopes, satellites, probes and knowledge.
Hubble Space Telescope uses many electromagnetic spectrum sensors
Solar Dynamics Observatory focuses on the Sun

16. What Causes the Seasons?
The tilt of the Earth’s axis as the planet is orbiting around the sun
The part of Earth angled towards the Sun gets more direct radiation  summer!

17. What season would this be
Seasons
If the northern hemisphere is tilted towards the sun, then it receives more solar energy during the day than the southern hemisphere.
What season would this be
for North Carolina?

18. What season would this be
Seasons
If the northern hemisphere is tilted away from the sun, then it receives less solar energy during the day than the southern hemisphere.
What season would this be
for North Carolina?

19. How Much is the Tilt?
The Sun’s rays hit the Earth at a more direct angle during summer than in winter
The tilts also causes longer daylight than nighttime during summer

20. Solstices
The days when the Earth’s tilt is at it’s maximum with regards to the Sun.
Notice how the Sun’s rays directly hit:
Tropic of Cancer during the summer solstice (A)
Tropic of Capricorn during the winter solstice (B)

21. Equinoxes Equinox - when the sun passes directly over the equator
The number of daylight hours equals the number of nighttime hours
“equinox” means “equal nights”
vernal equinox
autumnal equinox

22. Precession
Precession: change in direction of rotational axis – with no change in tilt (26,000 year cycle for Earth)
Rotational axis slowly traces out a cone
Due to nonspherical shape – Earth bulges outward at the equator
Rotation axis is the line in red

23. Nutation
The rocking, swaying or nodding motion in the axis of rotation of the Earth
It is the wobble around the precession axis
Precession axis is the line in white

24. Main cause: gravitational forces from the Moon, the Sun and the planets acting on Earth

25. Barycenter
Center of gravity around which two or more bodies revolve

26. Barycenter of Solar System
The Sun moves slightly as the gravitational pull of the planets tug on it as they rotate around the Sun.

27. The Moon
No light source – what we see is the reflection of the Sun’s light
Diameter of 2,000 miles
Between 3.8 and 4.6 billion years old

28. No Wind or Weather
No atmosphere – so surface temperatures of 127°C during day to -173°C at night (260°F to -280°F) Yikes!
No atmosphere or flowing water means no erosion
Neil Armstrong’s footprint will remain visible for 10 million years because there’s no erosion on the Moon

29. Impact Craters
Has lots of impact craters – craters formed when objects from space crash into the lunar surface
Earth had same bombardment of craters, but erosion erased evidence

30. Composition
Very similar to Earth, though not identical – mostly silicates
Iron poor – similar to Earth’s outer crust
Apollo 11 mission in 1969

31. Formation: Impact Theory
A Mars-sized object smashed into the Earth, spraying debris into orbit around the Earth
The debris reformed into the Moon
Also called “Ejected Ring” theory

32. Orbit
As the Moon rotates around the Earth, it also rotates around its own axis, keeping the same side facing the Earth. We can never see the “back” of the Moon from the Earth.
About 27 days for one orbit around the Earth

33. Phases of the Moon

34. Solar Eclipse
Occurs when the Moon passes directly between the Sun and Earth, blocking our view of the Sun.
Recall the Moon’s orbit is above and below the plane of the Earth and Sun, so the Moon does not often get between the Earth and the Sun

35. Lunar Eclipse Occurs when Moon passes through Earth’s shadow
Only during full moon, when the Moon is on the opposite side of the Earth from the Sun