1. The Moon and its Motions

2. The Earth’s Moon Satellite: a body that orbits a larger body Sputnik I: the first artificial satellite (1957) 1958: US launches 1 st satellite, Explorer I Moon: a natural satellite of any planet

3. The Earth’s Moon Moons gravity is 1/6 of that here on earth 1969 – 1972 six Apollo missions to the moon - found moving to be quite different Gravity has never been strong enough to hold gases, so no atmosphere Temperature variation 134ºC to -170ºC Very slow rotation of 29.5 days (about 4 earth weeks)

4. The Lunar Surface Light and dark areas Light areas are rough highlands composed of light colored rock Dark areas are called maria (Latin for sea) and are composed of dark solidified lava Rilles: long deep channels running through the maria

5. Rilles on the surface of the Moon

6. The Moons Craters Craters: bowl shape depression Most formed 4 billion years ago during the great bombardment Rays: displaced material from impact extending radially outward from the impact site Some are as large as 250 km Largest are named for famous scholars and scientists

7. Copernicus crater

8. Lunar Rocks Surface covered by a thin layer of dust caused by meteorite impact – material in this layer called regolith Depth of this regolith varies from 1m to 6m Same elements as rocks on earth but in differing amounts

9. Lunar Rocks Igneous rocks near surface are mostly oxygen and silicon Anorthosites: rocks from the highlands rich in calcium and aluminum – course grained and light-colored Rocks from the maria are dark-colored fine-grained basalts with titanium, magnesium, and iron

10. Lunar Rocks Breccia: fragments of other rocks that have melted together Lack elements with low melting points like sodium – burned off when the moon was molten Do not contain water

11. Moon’s Interior Information comes from seismographs Crust on side facing us is 60 km thick Crust on opposite side is 100 km thick and very mountainous Beneath the crust is the mantle which is about 1000 km thick – lower portion may still be molten Core may have a small iron core with a radius of less than 700 km No overall magnetic field

12. Development of the Moon Giant-impact hypothesis – Mars size body strikes the earth and ejected fragments eventually formed the moon 2 nd stage – covered by an ocean of molten rock – over time the minerals separated with those more dense materials migrating towards the core

13. The Moon’s Development 3 rd stage – outer surface cools forming the crust – meteorite bombardment Impacts decrease with time Geologic activity stopped with the cooling Moon similar today as it was 3 billion years ago

14. Movements of the Moon

15. Lunar Movement Orbit of the moon about the earth forms an ellipse Apogee: when the moon is furthest from the earth Perigee: when the moon is closest to the earth Average distance is 384,000 km (238,000 miles)

16. Lunar Movement Moon appears to rise and set each night Change of 50 minutes each day Moon also spins on its own axis Orbiting around the earth every 27.3 days similar to its rotation We see the same side of the moon all the time Moon rocks on its axis so we can see about 59% of the surface

17. The Lunar Cycle

18. The Moon’s Phases New Moon – moon is between the sun and the earth – no lighted area of the moon Waxing moon – when the amount of light on the surface we see is increasing – right side called a Waxing Crescent Moon First Quarter – half the lighted side is facing the earth – right half lit Waxing-gibbous – more than half is lit

19. Phases of the Moon Full moon – completely lit Waning – light is beginning to decrease Waning-gibbous moon Last Quarter Waning crescent Earthshine: sunlight that is reflected off the earth New Moon to New Moon is 29.5 days

21. The Calendar Day: time required for the earth to make one rotation on its axis Month: time required for the moon to go through one cycle of phases as it orbits the earth (29.5 days) Solar Year: time required for the earth to make one orbit around the sun (365.24 days)

22. The Problems 365 days is too short for a year and 366 days is too long 29 days is to short for a month and 30 days is too long Moon makes between 12 and 13 orbits around the earth in the time it take for the earth to orbit around the sun The calendar must account for these differences

23. The Julian Calendar 738 B.C. first calendar 304 days divided into 10 months 3 months behind the seasons Caesar’s astronomers revised the calendar Year was 12 months – 11 months had 30 or 31 days and February had 29 days – later one day was moved from February to August Leap Year compensates for extra day needed every four years 11 minutes longer than the actual solar year

24. The Gregorian Calendar By 1580 the calendar was about 10 days ahead of the season – Pope Gregory XIII dropped 10 days from the month of October to compensate Calendar revised and currently in use in most of the world 3 fewer days every 400 years Years ending in 00 and not divisible by 400 are not leap years (1700, 1800, 1900) Only 26 seconds longer than the solar year – only off by one day in 3000 years

25. Current Calendar Reform Thirteen-month calendar – each month to contain 4 weeks – new month called Sol between June and July – one day called year day would fall at the end of each year – every 4 th year leap day would be added to Sol. World Calendar – 12 months of 30 or 31 days – world day at the end of each year – leap day every 4 years at the end of June

26. Tides

27. The regular change in the height of the oceans Caused mainly by the moon and its gravitational pull This pull is strongest on the side facing the moon and weaker on the other side The difference between the strong force on one side and the weak force on the other is called a differential gravitational force

28. Tides The differential gravitational force draws water in the oceans into a tidal bulge There are two identical tidal bulges on either side of the Earth The Earth’s rotation carries us into these bulges As we enter the bulge the water level rises and as we leave the water level falls This creates two high tides and two low tides per day

29. What happens when these tides encounter the land? Water tends to pile up along the coastline The tidal bulge is typically about 2 meters This can turn into 10 meters in a narrow bay This may also cause water to rush up a coastal river in what is called a tidal bore

30. Lunar Motion and Tides Motion of the moon in its orbit causes the tidal bulge to shift slightly from day to day. High tides come about 50 minutes later each day (remember this is the same delay as moonrise)

31. Solar Tides The Sun also creates tides on Earth The Sun’s tidal force is about 1/3 that of the moons because it is so much further away Spring tides: abnormally large tides that occur during a new or full moon During spring tides the solar and lunar forces are working together

32. Solar Tides Neap tides: tides that aren’t as extreme as even normal high and low tides Happen during the 1 st and 3 rd quarter moon Sun and moon are at right angles to each other and therefore lessen the tidal effect

33. Spring Tide Neap Tide

34. Tidal Braking Tides create forces on both the Earth and Moon that slow their rotation We call this slowing of the rotation tidal braking As Earth’s rotation slows, the moon accelerates in its orbit causing it to move further from Earth (about 3 cm per year) This means that the Moon was once much closer to Earth and that Earth spun much faster (as fast as a day being 5 hours long several billion years ago) Earth has now slowed to its present 24 hour day Tidal braking lengthens the day by 0.002 second every century

35. Tidal Braking This works on the Moon as well even though there is no water. Earth’s gravity creates tides on the Moon which are distortions in its crust that slow its rotation as well This is what locks the moon in the synchronous orbit and why we see the same face all the time Eventually the Earth will be in synchronous orbit too and we will only be able to see the moon from one side of the planet

36. Tidal Braking The Moon’s gravitational pull on the Earth may also stabilize our climate by keeping the tilt of our axis fairly constant Without the pull of Moon’s gravity our axis would change erratically and with it we would have large changes in the severity of the seasons

37. Moon Lore The full moon triggers antisocial behavior (lunatics) Once in a Blue Moon – two full moons in a month – full moon on the first of the month – chances of this are 1 in 30 so this will happen about every 2.5 years More to the blue moon – has to do with particles in the atmosphere – normally blue colors are filtered out – but if the particles are just right the red is filtered out and the blue passes through

38. Moon Lore Harvest moon – the full moon nearest the autumn equinox Hunter’s moon – the full moon in October

39. Blue Moon

40. Harvest Moon