2nd Law of Thermodynamics

• 1st Law – conservation of energy• 2nd Law – no cyclic process which converts

heat entirely into work is possible.• Can’t build a perpetual motion machine• Entropy is a measure of disorder (random

motion of particles)• In all natural processes, the entropy of the

universe increases.

Order (opposite of entropy)O

rder

Time

Formation of the Solar System

Page 43-50

GWU AstronomyBob Fest

• Saturday January 25• 8-5 (9 first program)• Tucker Student Center

• 20 extra points test grade

Basic Materials

• Earth, Moon, Terrestrial Planets, asteroids, meteoroids, comets

• Heavy elements– Oxygen, silicon, aluminum, iron, carbon, calcium– Very Little Hydrogen and Helium

• Sun, Stars interstellar clouds– Light elements– Hydrogen, helium– 99% of all atoms, 98% of all mass

Big Bang• Not big and not a bang• Extrapolated the expanding universe back,

back, back in time• 13.5 to 14.6 billion years ago• An explosion that created all space, time,

matter and energy• Astronomy begins a few minutes after the

“beginning”

Limits of Science

• My Opinion• Science can not teach us what happened

“in the beginning” or before the “beginning”• I use the Genesis account– In the beginning, God created…– The universe is not a purposeless, random process

• You chose your faith

Heavy Elements

• Big Bang formed– Hydrogen, Helium, Lithium

• Heavier elements were formed in stars– Nuclear fusion– Hydrogen fused to form helium– Helium fused to form carbon– Carbon transformed into heavier elements• nitrogen, oxygen, neon, silicon, iron

Star Material Ejection

• Stellar Winds– Routine explosions expel outer layer

• Planetary nebulae– More energetic outburst

• Supernovae– Giant explosion formed heavier elements

Cone Nebula Page 131

Newly formed stars in Orion Nebula

Other Observations

• All planets orbit in the same direction• All planets orbit in a flat plane• Almost all planets spin in the same direction• Rocky planets near sun• Gas giants far from sun

Solar Nebula• The solar system formed from a fragment of a

vast cloud of interstellar gas and dust• Diameter of at least 100 AU• 2-3 times the mass of the sun• Collapsed due to– Winds from nearby stars– Explosion of another supernova– Pairs of clouds compressed each other– Radiated away enough energy to collapse

• Gravitational attraction collapsed further

Page 46

Protosun• Slowly rotating cloud• Deep inside the nebula, gravitational

attraction caused the gas and dust to “fall” to the center

• Pressure, density and temperature increased• Protosun• Atoms collided with each other producing

heat • Matter near center rotated faster

Protoplanetary disks

• Gravity, collisions and rotation produced irregular cloud fragments

• These fragments slowly came together • Formed larger objects planetesimals• Planetesimals collided and stuck together

forming protoplanets• Process of accretion continued for 100 million

years.

Computer Simulation (P47)

Outer Planets

• Core accretion model• Beginning with a “seed” rocky core• Attracted rock, gas, ices• Eventually the giant mass attracted hydrogen

and helium• Gas giants formed• Hydrogen and helium were pushed out of the

inner solar system by solar winds.

Meanwhile back at the Ranch

• Sun continued to heat up due to collisions of atoms

• Reached 107 K• Ignited hydrogen fusion• Star process – produces energy from fusion of

hydrogen into helium

Early solar system

• Very active place• Lots of debris• Lots of collisions- craters on moons

We see similar things in Orion Nebula

What the model explains

• Number and make up of terrestrial planets• Make up of Gas giants• Flatness of the Ecliptic• Rotation all in one direction• Craters on Moon and moons