Evolutionary History of the Solar System and the Earth

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Evolutionary History of the Solar System and the Earth

Earth Science 300

Summary Notes.

Evolutionary History of the Solar System and the Earth

Basics

temperature scales (ºF, ºC, K)

distances (mm, m, km, mm etc.)

periodic table (elements ordered by atomic number = # of protons)

structure of atoms (nucleus with protons, neutrons; outer electrons)

structure of simplest elements – H and He

isotopes

big bang theory of universe (15 billion years ago)

evidence for expansion of universe (red shift)

Stars

what is a star? (ball of hot gas of H, He)

process which generates Sun’s energy (fusion – converts H nuclei into He)

when it runs out of H fuel, star transforms into red giant

our sun takes about 10 billion years to do this (5 billion more to go!)

core keeps contracting – gets denser and hotter – more nuclear reactions

more elements created (by fusion)

most abundant (and important to life) are C and O

red giant of sun’s mass will last only a few hundred million years

next stage (after Red Giant) depends on mass of star ….

our sun:

fuel in our sun will eventually run out (another 5 billion years)

inner core will congeal into white dwarf

white dwarf: no more nuclear energy, becomes cool, dim and undetectable

elements locked up in star

more massive stars:

goes through nuclear process much faster, gets much hotter

many more elements synthesized (all elements up to iron, eg. Si, S, Ne)

some stars undergo a supernova explosion –

core collapses, sonic boom travels through star, it explodes

supernova shines as brightly as a billion suns

ejects its outer layers and releases chemicals

more elements are made in the shock wave

elements are cast out into space by the explosion

our sun is 99% H and He, and 1% heavier elements including iron – means that our sun was formed from previous generations of stars

the elements of the earth are the elements of the universe formed by earlier stars

Scale of the Universe

definition of light year

distance to sun (8.3 light minutes)

distance to next nearest star (4.3 light years)

size of Milky Way (100,000 light years across, contains billions of stars)

distance to furthest planet – Pluto (5.5 light hours)

nearest galaxy – Andromeda (2.2 million light years), has 300 billion stars

constellations – based on lore – not physically related

universe contains billions of galaxies

Our Sun

5 billion years old, will last for another 5 billion years

temperature at core = 15 million ºC

fusion takes place in core

heat travels by radiation, then convection

outer surface that we see = photosphere, temperature 5700 ºC

composition of our Sun = primarily H, He + traces of O, C, Na (sodium), Fe (iron)

We know composition from looking at absorption spectrum of Sun. Certain frequencies (wavelengths) of light are absorbed by gases in Sun’s atmosphere. These frequencies correspond to the energies needed to excite the electrons of the elements present into higher energy orbits – and uniquely identify the elements present.

Planets

planets grew by accretion (of cosmic dust = stardust = material created by earlier stars)

names (and order) of planets - MVEMJSUNP

motion of planets around the sun (Kepler’s Laws)

period of orbit increases as distance from Sun increases

Mercury shortest

Pluto longest

rocky planets = MVEM – earth-like. some have craters.

giant gas planets = JSUN – rich in H, He. V. hot internally. Cold at surface.

Jupiter’s Red Spot caused by huge storm in atmosphere of Jupiter

Saturn’s rings composed of ice

Earth

latitude and longitude

earth’s motion and seasons

The earth’s axis is inclined at 23 ½ º relative to the plane of the earth’s orbit around the sun. It is this tilt that is responsible for the earth’s seasons. (No tilt -> no seasons.)

The Earth is not always exactly the same distance from the Sun. (It travels in an ellipse, not a circle.) But the change in distance does not cause the seasonal temperature changes.

The earth spins on its axis once every 24 hrs.

The earth revolves in an elliptical orbit around the sun every 365 ¼ days.

Seasonal temperature changes are due to:

1. angle of noon sun

on any given day only places along a particular latitude will receive overhead (90º) sun. As we move N or S from this location the sun’s rays strike at an ever-decreasing angle. The more oblique the angle, the less intense the light.

At summer solstice (June 21) the sun is overhead at 23 ½ ºN (Tropic of Cancer)

At winter solstice (Dec 21) sun is overhead at 23 ½ ºS (Tropic of Capricorn)

At equinoxes (March 21, Sept 22) sun is overhead at Equator.

2. length of daylight

Need to compare fraction of line of latitude which is in daylight to that in dark to find # hours daylight vs # hours dark.

Equator always has 12 hrs day, 12 hrs night

At equinoxes everywhere has 12 hrs day, 12 hrs night

At June solstice everywhere in NH has more than 12 hrs day, less than 12 hrs night, number of daylight hrs increases as you go N, everywhere N of 66 ½ ºN has 24 hrs daylight. Opposite is true in SH. (i.e. Everywhere has less than 12 hrs day, more than 12 hrs night, number of daylight hrs decreases as you go S, everywhere S of 66 ½ ºS has 24 hrs night.)

At December solstice conditions are reversed for the two hemispheres over June solstice.

moon –

visible by reflected sunlight from its surface

orbit of the moon around the earth –

sidereal month = 27.3 days, synodic month = 29.5 days

spins once for every orbit around the Earth – same face always faces the Earth

phases of moon – new, first quarter, full, third quarter

positions of Earth, Sun and Moon during solar eclipse and lunar eclipse

Source : http://www.csun.edu/~hmc60533/CSUN_300/300_S2005_solar_system.doc

Web site link: http://www.csun.edu

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