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Midterm review A

Astronomy & Astrophysics
Course Code
Stefan Mochnacki
Study Guide

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totality of all space, time, energy, and matter
13.7 billion years old—birth at BIG BANG with only 2 elements:
hydrogen & helium …all other elements made by stars
light year = distance light travels in one year
limit on how far we can see, the universe is the OBSERVABLE
because light takes time to travel to us, looking far away = LOOKING
distance to nearest large galaxy is 2.5 million ly, therefore we see it as
it was 2.5 million years ago
planets stars (produce energy by nuclear fusion) solar system (1
or more planets orbiting a star) galaxy (collection of billions of starts
orbiting a common centerwe live in milky way galaxy) local group
(mw, Andromeda, and others orbit one another and make up local
group)galaxy clusters (moving apart from each other)galaxy
superclusters ( enormous groups of galaxies all orbiting one another)
AU (astronomical unit) –distance btw sun and earth
-SPEED = distance/time
-VELOCITY= speed and direction
-ACCELERATION=any change in velocity speed/time
-(g)acceleration of gravity- all falling objects accelerate at same rate despite
mass air resistance causes differences in acceleration
-momentum = mass x velocity
- force is the only way to change momentum causing acceleration ( -/+) 
NET FORCE=combined effect of all the individual forces put together
-ANGULAR MOMENTUM- rotational momentum of a spinning/orbiting
=mass x velocity x radius

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-mass is amount of matter (on moon body mass stays the SAME)
-weight is the force that a scale measures, depends on mass and forces
(gravity) acting on mass ( on moon you weight LESS because of weaker force
of gravity)
- weightlessness is due to a constant state of free-fall
NEWTONS LAWS OF MOTION object moves at constant velocity unless a net force acts to change
its speed/direction
2. force= mass x acceleration acceleration depends on an objects mass
and strength
3. for every force there is always an equal an opposite reaction force
CONSERVATION OF MOMENTUM- keeps planets rotating and orbiting the
total momentum of objects cant change unless an external force is
acting on them
interacting objects exchange momentum through equal and opposite
further from the sun a planets MOVES SLOWER
angular momentum = mass x velocity x radius
a.g cant change unless an external twisting force (torque) is acting on
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