The Earth in Space

The Solar SystemInner Planets

The Earth-Moon-Sun System

Phases of the Moon

The Moon’s Orbit and Rotation

The Moon makes 1 rotation per orbit. Why?

(Solid) Tides

The Moon is pulled into anoblong shape So is the Earth,

but to a lesser extent.Mostly the oceans are affected

Putting on the Brakes on the Early Moon

Earth pulls on the moonSlowing it down

Eventually the Moon’s rotation slowed toonce per revolution

Putting on the Brakeson the Earth

Moon pulls on the Earth’s oceans, which sloshagainst the continents. This slows down the Earth.

Our days are getting longer by about 0.016 seconds per century400 Ma ago, the day was 22 hours long! (400 days/year) (coral)900 Ma ago, the day was 18 hours long! (486 days/year) (sed rx)

Seasons, Tropics, and Circles

How hot would the Earth be if there was no atmosphere?

• What is the average temperature of the moon?– The moon’s soil is ~252 K, or -21°C on

average (Little et al, 2001, AGU Abstracts)• (K = °C + 273.15)

Blackbody RadiationObservation: When something gets hot, it

begins to glowFirst, dark redThen, bright redThen, yellowEventually, blue

Note: This is NOT related to which part of a flame is hottest

Blackbody Radiation

Infrared

Ultr

avio

let

• Maximum Wavelength?– Wien Displacement Law Max (m) = 2898/T

• Total amount of Energy Emitted– Stefan-Boltzmann Law– E (W/m2) = 5.7 x 10-8 T4

• T in degrees Kelvin

Blackbody Radiation

Blackbody Radiation

• What’s the Point?– Any body, at any temperature greater than

absolute zero, is emitting light– Cool objects emit light we can’t see with

our naked eye (in the infrared)– Emitting light means that the objects are

emitting energy (in the form of light), and thus are losing energy

So, what temperature should the Earth be?

• It’s a simple calculation:– Energy hitting the Earth from the Sun must

equal the energy leaving the Earth– 1367 W/m2 is hitting the Earth from the Sun

• But 30% of it is reflected back to space– Albedo = 0.3

• Leaving 973 W/m2 at the Equator

We have to figure out what the AVERAGE amount of light is hitting the entire Earth

This is the amount hitting the Earth at the Equator (973 W/m2)

Times the area of the EARTH’S DISK (=r2)

Divided by the Earth’s total SURFACE AREA (=4r2)

So, what temperature should the Earth be?

• It’s a simple calculation:– Energy hitting the Earth from the Sun must

equal the energy leaving the Earth– 1367 W/m2 is hitting the Earth from the Sun

• But 30% (planetary albedo) of it is reflected back to space, leaving 973 W/m2 at the Equator

• So, there’s an average of 243 W/m2 over the entire surface

– (5.67 x 10-8 * T4) W/m2 are leaving the Earth

So, what temperature should the Earth be?

• The Answer: -18.3°C – The average temperature of the Earth is really ~

15°C– The Greenhouse effect is ~33°C [ 15° - (-18°) ]

• 4 Ga ago, the sun was 30% fainter, but the Earth was warmer– Equilibrium temperature with faint early sun: -40°C

• A Paradox?

What Impacts Insolation?

• Sunspots– 11 year cycle

• The Eccentricity of the Earth’s Orbit– 100 ka cycle and a 413 ka cycle

What Impacts Insolation?

• The Tilt of the Earth’s Axis– 41 ka cycle

What Impacts Insolation?

WarmerSummer

CoolerSummer

• The wobble of the Earth’s axis and its orbit (precession) - 23 ka cycle

What Impacts Insolation?

11,500 years ago

26 ka 112 ka

What is the impact of changes in insolation?

• How much of a difference does 30 W/m2 make?

• -18.99°C to -17.59°C

• A range of 1.4°C

Earth’s Orbit in the News….

Aurorae

• Aurora Australis (Southern Hemisphere)

• Aurora Borealis (Northern Hemisphere)

http://dotearth.blogs.nytimes.com/2008/11/14/from-above-animated-aurora/?hp

The Magnetosphere

• The Earth has a Magnetic Field that extends into space

The Solar Wind• The Sun emits charged particles that

spew into space– The amount of particles increase during

high sunspot activity– And coronal mass ejections (solar flares)

Contact, the origin of the aurorae

Aurorae on other planets

• Also– Mars– Neptune