Unit 4: The Moon Mr. Ross Brown Brooklyn School for Law and Technology

In this unit we will learn about: The primary surface features on the Moon and how they differ from Earth The effect of impacts on the Moon The Moon’s internal structures The absence of atmosphere or internal activity on the Moon The Moon’s orbit Theories of the Moon’s formation How the Moon’s gravity causes tides on Earth

How did the Moon’s surface develop its features? 9 May 2016 Do now: Why do we see the face of ‘the Man in the Moon?’

The Moon

How did the Moon’s surface develop its features? Lunar Maria (singular is Mare): large, smooth, dark areas on Moon’s surface, from Latin word for “seas” as they were mistaken for oceans. Dark because made of basalt. High in iron and magnesium (mafic).

How did the Moon’s surface develop its features? Bright areas are Highlands. High in silicates and calcium, thus lighter. Also, less dense than maria, and much older than maria. Highlands have many more craters. – Which are older, maria or highlands? Many craters have rays radiating outward.

How did impacts shape the surface of the Moon? Impacts result in craters, with material pushed outward to form crater rim Early impacts pierced lighter crust, resulting in lava seeping up to fill craters (Maria) Fewer impacts after Maria were formed

How does the Moon’s structure differ from the Earth? 10 May 2016 Do now: In what ways does the Moon differ from the Earth geologically?

How does the Moon’s structure differ from the Earth? Volume/ surface area is smaller – Heat escapes easily Less (or no) convection – no tectonics Covered in regolith: blanket of rock – Chunks, powder Moon Density is 3.3 g/cm3 Earth density is 5.5 g/cm3 Moon has little iron No magnetic field

How does the Moon’s structure differ from the Earth? Astronauts left seismic detectors behind Crust is much thinner on side facing Earth – Few maria on far side – Heavily cratered

How does the Moon’s structure differ from the Earth? Little or no atmosphere – 1 quadrillionth of Earth’s – If any water, frozen near poles (comets?) Why no atmosphere? – No volcanic activity to produce gases – Not enough gravity to hold an atmosphere Remember escape velocity!

How else is our Moon special? 11 May 2016 Do now: Where did our Moon come from?

What makes the Moon’s orbit unique? Elliptical orbit of Earth – Distance from Earth varies – Average is 380,000 km (250,000 miles) – Size in sky varies by 14% Synchronous rotation (you know this!) – Common characteristic of satellites

How else is our Moon unique? Moon’s orbit is tilted by 5° relative to the ecliptic (Earth’s orbit around the Sun) Including Earth’s 23.5° axial tilt, the Moon’s tilt varies from 18° - 29° from our equator

How else is our Moon unique? Our Moon’s mass is 1/81 our Earth’s Other satellites have masses of less than 1/1000 of their planets. This suggests our Moon was formed in a special way!

Where did our Moon come from? Before Apollo missions, we had many theories Rock samples from Moon challenged theories Now we believe: – Mars-sized body hit the Earth long ago (4.5 BYA) – The debris became the Moon – This would explain Moon’s orbit and composition

Moon’s Creation

What causes the tides? 12 May 2016 Do now: What causes the tides? No, it’s not enough to say “the Moon.” Why do the tides change throughout the day and why are they different everyday?

What causes the tides? Side of Earth near the Moon feels more pull from gravity – differential gravitational force Tidal bulge – swelling on two sides of Earth Why does the bulge develop on 2 sides?

Watch Science on the Spot video What causes tides? What is the Spring Tide? What causes it? When does it occur? What is Neap tide? What causes it? When does it occur? What has happened to the sea level of San Francisco Bay since 1900? What makes the Bay of Fundy special?

How does the Sun contribute to tides? Sun and Moon pulling on Earth in-line: Spring Tides – extra large at New and Full Moon Sun and Moon at 90°angles relative to Earth: Neap Tides – smaller tides when Sun and Moon offset each other

How else do Tides affect the Earth? Tidal braking: As the Earth spins, friction drags the tidal bulge ahead of the imaginary line connecting Earth and Moon. The Moon’s gravity pulls back on the Earth, slowing it. Tidal bore: The leading edge of a tide racing through a narrow inlet.