Unit 2

1. Unit 2 ‘The Universe’

2. Early Astronomy • Many discoveries are credited to scientists from Greece • 1. Geocentric Model • People once thought Earth was the center of the Universe • They thought the moon, Sun, and other planets orbited Earth

3. Early Astronomy Geocentric Model: In this 1st model, the Sun revolves around the EARTH.

4. Early Astronomy *Scientists in the 16th and 17th centuries made observations that made this model difficult to accept – it did not make sense based on what they were seeing. So they came up with:

5. Early Astronomy • 2. Heliocentric Model • People changed their thinking to the Sun being the center of the solar system instead of the Earth • So, they finally believed that the planets and moons orbit around the Sun

6. Early Astronomy • Heliocentric Model In this model, the earth revolves around the SUN.

7. Modern Astronomy Objects in space are in motion – they move!:

8. Movement in Space Spinning in place; like a dradle • A. Rotation • Spin of a body on its imaginary axis • On Earth: • Rotates once every 24 hours • Causes day and night

9. Movement in Space Rotation

10. Movement in Space • B. Revolution • Movement/orbit of a body around a larger one • Earth revolves around the Sun and the moon revolves around Earth • Earth revolves around the Sun once a year (every 365 days)

11. Movement in Space Revolution

12. Movement in Space • Orbit is elliptical (oval-shaped) so the distance from the sun changes 1. Perihelion – Earth is closest to Sun (1/3) 2. Aphelion – Earth is farthest from Sun (7/4)

13. Movement in Space Farthest Nearest

14. Gravity • C. Force of Gravity • Gravity = the force of attraction between 2 objects • Depends on the mass of each object and the distance between them

15. Gravity • Greater mass = greater force of gravity • Less of a distance between objects = less force of gravity • Gravity holds planets and other space objects in their orbits

16. Distance in Space • 2. Measuring Distance in Space A. Light year – unit of measure for the distance between objects in space • Distance light travels in 1 year • Light travels about 5.8 million miles a year • Travels 186,000 miles per second

17. Distance in Space

18. Objects in Space - Moon • A. The Moon • Earth’s only natural satellite • May have formed when a body the size of Mars struck Earth and resulted in a part of Earth breaking off

19. Objects in Space - Moon

20. Objects in Space - Moon

21. Objects in Space - Moon • Characteristics: • Rotates once on axis every 29 days • Revolves once around Earth every 29 days – so only see 1 side of moon • No atmosphere or water • Many craters • 1/6 the gravity of Earth

22. Objects in Space - Moon • Phases of the Moon – during its trip around Earth, the lighted area of the moon seems to change shape • Moon reflects the light of the Sun • Starts with new moon • Moon and sun are on the same side of Earth • Dark side faces the Earth – cannot see moon

23. Objects in Space - Moon

24. Eclipses • Eclipses: • Occur when 1 body passes through the shadow of another.

25. Eclipses • Types: 1. Lunar Eclipse – Earth is between moon and Sun 2. Solar Eclipse – Moon is between Earth and Sun

26. Eclipses

27. Solar Eclipse

28. Solar Eclipse Can you see the small dot in the middle of the circle? That is the moon blocking out the SUN.

29. Solar Eclipse

30. Lunar Eclipse Notice that the MOON is being blocked out.

31. Tides • Tides: • Rise and fall of the ocean that occurs twice a day • Cause of tides = gravitational pull from moon • Pulls on one side of Earth, then the other

32. Our Solar System • 1. Facts: • Contains planets, moons, stars, comets, asteroids, etc. • About 4.6 billion years old • Big Bang Theory – Theory that a huge explosion created the universe about 20 billion years ago

33. Our Solar System • 2. Within our Solar System: A. Planets: • 2 groups: • Inner • Rocky (terrestrial) planets – mostly rock with little gas (smaller) • Mercury, Venus, Earth, Mars

34. Inner Planets

35. Inner Planets VENUS MERCURY SUN MARS EARTH

36. Our Solar System • Outer • Gas giants – large planets – small liquid/rock core surrounded by mostly gas • Jupiter, Saturn, Uranus, Neptune

37. Outer Planets

38. Our Solar System • Dwarf Planets • Too small to be an actual planet • Ceres – in asteroid belt • Pluto and Eris – orbit beyond Neptune

39. Pluto

40. Ceres and Eris

41. Our Solar System • Surface temp on planet depends on its distance from the sun • Mars and Venus are the hottest • Venus is the hottest planet – has a very dense atmosphere with lot of carbon dioxide (greenhouse gas that traps sun’s heat)

42. Greenhouse Effect

43. Our Solar System • Planets revolve around sun because sun’s gravity is so great

44. Facts about the planets

45. Facts about the planets

46. Facts about the planets

47. Facts about the planets

48. Earth • Seasons on Earth - due to Earth’s tilt at 23 ½ degrees • Earth is closest to the sun in the winter and farthest from the sun in the summer • The tilt is what determines how cold or hot it is

49. Earth • 1. Equinoxes • When there is exactly 12 hours of daylight • Vernal (spring) equinox- – around 3/21 • Autumnal equinox (fall) – around 9/22

50. Earth • 2. Solstices – Depends on the length of the sun’s path through sky • Summer = longest day of year (greatest amount of daylight) • Winter = shortest day of year (shortest amount of daylight)