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Chapter 12

Chapter 12. 12.1 – The Solar System. Humans have been aware of the relationships between the Earth, Sun and Moon for thousands of years, but only recently have we began to better understand the true nature of these relationships.

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Chapter 12

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  1. Chapter 12 12.1 – The Solar System

  2. Humans have been aware of the relationships between the Earth, Sun and Moon for thousands of years, but only recently have we began to better understand the true nature of these relationships. • Astronomy is an area of science which observes and explains events and objects outside of Earth and is atmosphere.

  3. Earth’s Moons • Rotation (spin on axis) & Revolution (around sun)

  4. Earth’s Moons • Rotation = 24 hours Revolution = 365 days • Earth’s tilt = 23.5 degrees

  5. Earth’s Rotation • Rotation of earth creates the night and day. • Photoperiod = hours of daylight between sunrise and sunset • Ancient Greek astronomers would observe the 12 main constellations and five bright lights (planets) • Constellations and planets usually rise in the east and set in the west • Retrograde motion: Planet looks like it loops back and goes forward • http://www.youtube.com/watch?v=72FrZz_zJFU

  6. Precession • The change of Earth’s axis. Happens slowly over 26 000 years

  7. EARTH’S REVOLUTION • Takes approximately 365 ¼ days to rotate once around the sun • Revolution is ELIPTICAL (not circular) • Aphelion – Earth farthest from sun (around July 4)  S.H. Summer Therefore higher temp & more desserts in S.H. & colder Antarctic. • Perihelion – Earth is closest to sun (around January 3)  N.H. winter

  8. When is summer in Canada? • When is summer in South Africa? • Why does this happen?

  9. The Seasons • Caused by TILT of earth, not orbit around sun • http://www.youtube.com/watch?v=000-3JYM0NI

  10. Constellations • Star patters (currently 88 in total) • Patterns that aren’t an official constellation are asterisms • Big Dipper is an asterisms  part of Ursa Major • Names taken from Greek & Arabic Mythology • Stars are so far away, motion relative to earth is very slight. But, over thousands of years, we would see a change.

  11. The celestial sphere • Middle Ages (450-1450CE) people thought sky was solid and stars were attached to an invisible crystal sphere. • Planets were closer to Earth so they were attached to their own sphere. • Thought that this sphere rotated around earth. • Celestial sphere is an imaginary sphere where all the objects in the universe lay (constellations, planets). Earth is the centre.

  12. Celestial Equator separates the sphere into northern and southern sections. • North Celestial Pole • South Celestial Pole • The path the sun takes through the sky is called the plane of the ecliptic

  13. Because or Earth’s tilt, angle between celestial equator and ecliptic is 23.5 • Spring Equinox = March 21 Fall Equinox = September 22 • Date when sun (on ecliptic) crosses celestial equator • Number of hours sun is above and below horizon is equal • Summer Solstice = June 21 Winter Solstice = December 21 • Sun reaches highest and lowest position in sky. Earth tilted farthest away or towards sun. • Summer solstice = longest day in year (longest photoperiod)

  14. Circumpolar Constellations • Constellation that is on the horizon and never disappears • Ursa Major • Ursa Minor • Cassiopeia

  15. CYU – p375 #4, 8, 10, 12, 17, 19, 20

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