The Earth in Space

The Solar System Inner 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 an oblong 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 moon Slowing it down Eventually the Moon’s rotation slowed to once per revolution

Putting on the Brakes on the Earth Moon pulls on the Earth’s oceans, which slosh against the continents. This slows down the Earth. Our days are getting longer by about seconds per century 400 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)

Earth’s Ocean Tides Sun + Moon –Spring Tide Sun - Moon –Neap Tide

The Earth-Sun System The Earth’s orbit is nearly circular –Orbital Period = days –Eccentricity = (has varied from to 0.06) –Mean Radius = ~1.5 x 10 8 km The Earth revolves around its axis –Once per day –With an inclination of ~23.5° relative to the plane of the ecliptic (varies from 22.2° to 24.5°)

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 )

Blackbody Radiation Observation: When something gets hot, it begins to glow First, dark red Then, bright red Then, yellow Eventually, blue Note: This is NOT related to which part of a flame is hottest

Blackbody Radiation Infrared Ultraviolet

Maximum Wavelength? –Wien Displacement Law – Max (  m) = 2898/T Total amount of Energy Emitted –Stefan-Boltzmann Law –E (W/m 2 ) = 5.7 x T 4 T in degrees Kelvin 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/m 2 is hitting the Earth from the Sun But 30% of it is reflected back to space –Albedo = 0.3 Leaving 973 W/m 2 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/m 2 ) Times the area of the EARTH’S DISK (=  r 2 ) Divided by the Earth’s total SURFACE AREA (=4  r 2 )

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/m 2 is hitting the Earth from the Sun But 30% (planetary albedo) of it is reflected back to space, leaving 973 W/m 2 at the Equator So, there’s an average of 243 W/m 2 over the entire surface –(5.67 x * T 4 ) W/m 2 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? Warmer Summer Cooler Summer

The wobble of the Earth’s axis and its orbit (precession) - 23 ka cycle What Impacts Insolation? 11,500 years ago 26 ka112 ka

What is the impact of changes in insolation? How much of a difference does 30 W/m 2 make? °C to °C A range of 1.4°C

Earth’s Orbit in the News….

Aurorae Aurora Australis (Southern Hemisphere) Aurora Borealis (Northern Hemisphere)

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