1. Ch 22 - Origins of Astronomy  Astronomy = study of the universe Began in Greece 600 BC-150 AD ○ Aristotle = discovered Earth was round because it always casts a curved shadow when it passes between the sun and the moon

2. Eratosthenes = found size of Earth by comparing angles of sunlight between 2 cities circumference of Earth = 40,075 km

3. Hipparchus = created star maps, calculated the length of a year to within minutes, and developed predictions for lunar eclipse times

4. Early Models of Solar System 1. Geocentric Model = the moon, sun, and the known planets (Mercury, Venus, Mars, and Jupiter) orbit around Earth

5. Geocentric Cont’d Most Greeks believed in this model All bodies rotated in a perfect circle around Earth Stars were in the celestial sphere Dominate view for 2000 yrs

6. 2.Heliocentric Model = the Earth and the other planets orbit the sun Developed by Aristarchus (Greek, 312- 230 BC) Utilized geometry to calculate the distance between Earth to sun and Earth to moon

7. 3. Ptolemaic System = model that accounted for movements of the planets - Developed by Claudius Ptolemy - Planets moved in circular orbits around a motionless Earth - Explained Retrograde Motion

8. Observation: Each planet moves slightly East in the night sky, However, each planet appears to stop periodically, reverse direction for a time, & then resume an eastward motion Explanation: Results from the combination of the motion of Earth and the planet’s own motion around the sun

9. Modern Astronomers Nicolas Copernicus (1473-1543) from Poland Concluded that Earth was a planet and it rotates daily Sun centered model of solar system and Mercury, Venus, Earth, Mars, Jupiter, and Saturn orbit around it

10. Tyco Brahe (1546-1601) from Denmark  Developed observatories  Detailed observations of Mars  Trained Kepler

11. Discovered 3 laws of Planetary Motion: 1. Planets travel in Ellipses (oval shaped) around the sun 2. Each planet covers equal areas in equal amounts of time, so the planets travel faster when they get nearer the sun and slow down as they get further away Johannes Kepler (1571-1630)

12. 3.The length of time it takes for a planet to orbit the sun and the distance to the sun are proportional = planets farther away from the sun take a longer time to make 1 revolution around the sun - Expressed distances in space in Astronomical Units (AU) 1AU = average distance between the Earth and the sun = 150 million km Compared distance with revolution time around sun:P 2 = a 3 P = orbital period (time) around sun a = distance from sun

13. Galileo Galilei (1564-1642) from Italy - Developed modern telescope - Discovered 4 major moons orbiting Jupiter (disproved Earth-centered model) - Discovered that planets are circular (Earth- like)

14.  Found that Venus had phases similar to the moon = Venus orbits the sun  Discovered that moon’s surface was not smooth  Discovered sun had dark spots on surface (Sunspots) and found sun’s rotational period was ~ 1 month -

15. Sir Isaac Newton (1642-1727)  - Explained the forces in planetary motion = Law of Universal Gravitation every “body” in the universe attracts every other “body” with a force proportional to size and inversely proportional to their distance Meaning = larger object have a lot of gravitational pull but this depends on how close you are

16. Motions of Earth  Rotation = turning or spinning of a body on its axis EX: Earth rotates on its axis 1 time per day - Earth’s axis is tilted ~23.5° = controls amount of direct sunlight - creates Earth’s seasons  Revolution = the motion of a body along a path around some point in space EX: Earth revolves around the sun 1 time each year Earth revolves around the sun at a speed of 107,000 km/hr - Earth’s distance from the sun changes depending on the time of year

17. Perihelion = Earth is closest to sun (~ 147 million km), occurs on January 3 rd - Aphelion = Earth is farthest away from sun (~ 152 million km), occurs on July 4th

18.  Precession = slight movement (over a period of 26,000 yrs) of the Earth’s axis Earth’s axis remains at same angle BUT direction in which the axis points is continually & slowly changing (Earth wobbles) Right now our axis points to North Star (Polaris) and all stars appear to rotate around this point in sky In 14,000 yrs, axis will point toward Vega In 26,000 yrs, axis will point back toward Polaris This does not affect seasons because tilt doesn’t change

19. Phases of the Moon  Moon revolves around Earth every 27 1 / 3 days  Moon rotates on its axis every 27 1 / 3 days Because revolution & rotation of moon are same, we always see the same side of the moon ○ Sunlight side of moon = 127° C ○ Dark side of moon = -173° C  Lunar (moon) phases result from: the motion of the moon and the sunlight that is reflected from its surface

20. The 8 Phases of the Moon

21. Phase 1: New Moon = no moon visible

22. Phase 2: Waxing Crescent Moon = thin sliver visible, each day more moon is visible

23. Phase 3: First Quarter = half of moon is visible

24. Phase 4: Waxing Gibbous Moon = more than half of moon is visible, each day more of moon is visible

25. Phase 5: Full Moon = complete disk of moon is visible

26. Phase 6: Waning Gibbous Moon = more than half of moon is visible but each day less of moon is seen

27. Phase 7: Third Quarter Moon = half of moon is visible

28. Phase 8: Waning Crescent Moon = thin sliver is visible but each day less of moon can be seen - New Moon follows and cycle repeats

29. Eclipses  Eclipses are just shadows created by the relative positions of sun, moon, and Earth Solar Eclipse = when the moon moves in between the Earth and the sun, a shadow is created on the Earth, and the sun is temporarily blocked from view on Earth - occurs during new moon phases - only small areas are affected (275 km wide) and very short (~ 7 minutes) - Next total solar eclipse visible in US is 8-21-2017

30.  Lunar Eclipse = occurs when the Earth moves in between the sun and the moon, and the moon is temporarily blocked from view on Earth (by the Earth’s shadow) occurs during full moon phases can last up to 4 hrs and is visible to 1 / 2 of Earth  For either type of eclipse to occur, the earth, moon, and sun must be perfectly aligned within the same orbital plane  usually only happens 4 times a year  partial eclipses can occur if planets are not perfectly aligned

31. Earth’s Moon  Compared to other planets and their moons, our Moon is very large 1 / 4 size of Earth at 3,475 km diameter  Best studied during Apollo missions 6 Apollo missions landed on the moon during 1969 to 1972  Less dense than Earth (because of very small iron core)  1/6 the gravity of Earth

32. Earth’s Moon  2 types of lunar landscapes: 1. Dark Lowlands / Maria = ancient beds of basaltic lava, very smooth 2. Bright Highlands = deeply pitted, mountainous, found mostly on the far side of the moon - Lots of Craters = rounded depressions caused by impact of space debris (EX:meteorites)

33. Earth’s Moon - Because the moon has no atmosphere, debris can freely impact surface ALSO no weathering so craters are never destroyed  All of moon is covered with gray debris from billions of years of meteor bombardment = created a soil-like layer of lunar dust = Lunar Regolith (3m thick)

34. Earth’s Moon’s History  The most widely accepted model for the origin of The Moon is: - At the beginning of the solar system, when everything was still molten, a body the size of Mars impacted Earth - This impact liquefied Earth’s surface and ejected huge amounts of crustal and mantle rock from the newly formed Earth - A portion of this ejected material began to orbit the Earth and became The Moon ~ 4.5 billion yrs old

35. Earth’s Moon’s History - The early moon was continually impacted as its gravity pulled in space debris - Maria basalts formed later (~3.5 billion yrs ago) as the crust cooled - The Moon hasn’t changed much since its origin

36. Science Starter 22.1 Go to the SS section of your binder. Copy the following question and answer it. Be sure to label it SS 22.1 and date it. What is astronomy?