[ASTR 5] - Midterm Exam Guide - Ultimate 21 pages long Study Guide!

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6 Feb 2017
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ASTR 5
MIDTERM EXAM
STUDY GUIDE
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ASTR 5 Week 1 Notes
Lecture 2
Bringing context to our search
I. Universe is vast and old.
Lightyear (ly) : unit of distance, (speed of light)*(seconds in 1 year)
~ 10 trillion km / 6 trillion mi
When we look at something a billion lightyears away, we look at an image of what it
looked like a billion years ago
Speed of light = 300k km/s / 670m mph
Giga (G) = Billion
II. Elements of life are widespread.
III. Same physical laws operating on Earth operate throughout the universe.
Earth
Rocky planet that takes about 50 hours to circle at the Equator. Mass: 6E24 kg
Spins on axis once per day while moving in a huge orbit around the Sun per year (the two are
not related)
Time for light to travel from Sun to Earth is ~8 min 20 s
Space
Space is really empty. Everything in the solar system excluding the Sun added up ~ mass of 2.5
Jupiters
Sun is ~ 10 Jupiters in diameter, ~ mass of 1k Jupiters
Neptune = 30*Earth's distance from the Sun, or 30 AU
Astronomical Unit (AU) : 150 million km / 93 million mi
Planets are tiny compared to distances between them
Interesting : Venus' axis is upside down (moving backwards), while Uranus is on its side
Putting everything into perspective
Sun = grapefruit (10 billion times smaller) Earth = tip of the ballpoint pen
Jupiter = marble Sun - Neptune ~ 4 football fields
The nearest star is the Alpha Centaurus triple system.
The distance from the Sun in the scale above would be 2 grapefruits, one in LA and one in
Washington DC, with it taking 4.2 years for light to travel one way.
Our Sun is only one star in 200 billion+ stars in our galaxy, with every star orbiting around the
center of the Milky Way
The Sun
Only star in the solar system that generates its own light. Everything else has reflections of
the sun's light.
Contains 99.9%+ of solar system's mass, consists mostly of ionized plasma (H/He gas), very hot
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Converts 4m tons of mass into energy per second
Galaxy
Enormous island of stars held together by gravity and orbiting a common center
Planet : moderately large object that orbits a star, shining by reflected light. Can be rocky, icy, or
gaseous.
Moon : object in orbit around a planet.
Asteroid : Relatively small and usually misshapen, rocky object that orbits a star.
Comet : Relatively small and icy object that orbits a star. Can be called a dusty snowball as it also
contains some rocks.
Planet order : Sun, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto
Terrestrial planets : Mercury - Mars
small size and mass, mostly rock and metal, solid and warmer surface
Jovian planets : Jupiter - Neptune
bigger size and mass, mostly H/He/H compounds, no solid and cooler
Nebular Theory
Nebula = cloud, theory explains the origin of the solar system .
Starting with a huge cloud of mostly H atoms that slowly spins and contracts on itself, causing it
to rotate faster and heat up. Collisions flatten the cloud into a disk shape. When the temperature
at the center reaches a certain height, a star forms. However, temperature decreases with
distance from the center.
Frost Line: critical distance where inside it only rock and metal condense, while beyond
it ice will form. (Ice can create much bigger objects as they can stick things together)
Our Frost Line lies between Terrestrial and Jovian planets.
Small pieces of matter condense and become planetisimals , which are drawn together by
gravity to form larger clumps that eventually become planets. Assembly from smaller parts is
called accretion . The disk process repeats, but in smaller scale, when moons form. Comets and
asteroids are the leftover planetesimals.
When meteorites hit us, we use radioactive age dating to find out how old the solar system is
(4.6 billion years), as meteorites haven't changed since they accreted.
Atoms
92 different elmeents occur in nature, with H most abundant, He #2, and O #3
Atomic number = proton # = Z, unique for each element
Atomic mass number = proton + neutron = A = Z + N
Protons have +1 charge, electrons have -1 charge, neutrons have no charge.
Isotopes : atoms with different numbers of neutrons
As stars form and die, their intense heat makes heavier elements and recycling the other
elements. Because heavy elements are necessary for life, it takes time for life to arrive in
the universe.
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