1. Earth in Space Section 19.1

2. Earth’s Shape Considered to be ellipsoid Oblate spheroid Earth is wider than it is tall Bulges at equator, flattened at poles

3. Earth’s motions Rotation – spinning on an axis - causes day and night The earth moves toward the east causing the sun to appear to move to the west

4. Earth’s Motions 1. sidereal day The time it takes the Earth to rotate once with respect to a reference star. One 360° Rotation Time = 23 hr. 56 min. 1-2: Globe rotates 360° - sidereal 1-3: Globe re-points to sun - synodic

5. Earth’s motions 2. solar (synodic) day = 24 hours The time it takes Earth to rotate once with respect to the sun. (Sun’s Highest point in sky to the next highest point in sky).

6. Earth’s Motions Revolution – movement around a fixed point (sun) The path of the earth’s revolution around the sun is called an orbit

7. Earth’s Motions - Revolves once every 365.25 days (year) need leap years - elliptical shaped orbit - Jan. 3 - 147 million km from sun - July 4 - 152 million km from sun

8. Seasons on Earth Earth’s axis is tilted 23.5 o The area tilted towards sun has longer days and more radiant energy (summer) The area tilted away from the sun has shorter days and less radiant energy (winter)

9. Seasons on Earth http://www.google.com/url?q=http://www.a stronomy.org/programs/seasons/&sa=U&ei =ZmKqT_ucDKaN6QHvreHBBA&ved=0CC4 QFjAI&usg=AFQjCNGSxsNkGIzK6LUgpd7s 0ZgkrOxDZghttp://www.google.com/url?q=http://www.a stronomy.org/programs/seasons/&sa=U&ei =ZmKqT_ucDKaN6QHvreHBBA&ved=0CC4 QFjAI&usg=AFQjCNGSxsNkGIzK6LUgpd7s 0ZgkrOxDZg

10. Winter solstice Dec 21 or 22 Shortest day Summer solstice June 21 or 22 Longest day Vernal equinox March 20 or 21 Autumnal equinox Sept 22 or 23 Solstice – the sun reaches the greatest distance north or south of the equator Equinox- the sun is directly above the equator. Equal daylight and night time hours all over the world

11. Earth’s Motions Precession – Earth’s wobble

12. Law of universal gravitation: every object in the universe attracts every other object. Earth’s Orbit Isaac Newton

13. Attracts all objects towards each other.

14. Depends on two factors: MASS THE DISTANCE The amount of matter (stuff) in an object STRONGER

15. MASS The amount of matter (stuff) in an objectThe amount of matter (stuff) in an object Does not changeDoes not change WEIGHT Force ( a push or pull) of gravity on an object.Force ( a push or pull) of gravity on an object. Changes depending on where you are.Changes depending on where you are. VS

16. 265 lbs About 45 lbs =120 x 1.6

17. Earth’s Orbit Inertia – the tendency of an object to resist change in motion Newton’s first law of motion An object in motion will stay in motion, in straight line, at a constant speed unless acted upon by an outside force http://www.seasky.org/solar- system/planet-weight-calculator.htmlhttp://www.seasky.org/solar- system/planet-weight-calculator.html

18. Earth’s Orbit Inertial force Gravitational force Newton concluded that 2 forces (inertia, gravity) combine to keep Earth in orbit around the sun