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Midterm #1 Study Guide!!! This is a must download, very DETAILED!

by OC4

Astronomy & Astrophysics
Course Code
Clifford Orwin
Study Guide

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AST101 – The Sun and Its Neighbours
Midterm #1 – Study Notes
Chapter 1 – 5
Chapter 1 Our Place in the Universe
GEOCENTRIC earth-centered universe
SOLAR SYSTEM (star system) consists of a star (sometimes more than one star) and
all the objects that orbit it [consists of the Sun and all the objects that orbit it: the
planets and their moons, asteroids (chunks of rocks), comets, and countless tiny particles
of interplanetary dust]
MILKY WAY Used both as the name of our galaxy and to refer to the band of light we
see in the sky when we look into the plane of the Milky Way Galaxy
GALAXY a huge collection of anywhere from a few hundred million to more than a
trillion stars, all bound together by gravity
LOCAL GROUPthe group of more than 30 galaxies to which the Milky Way Galaxy
GALAXY CLUSTERS (cluster of Galaxies) a collection of a few dozen or more
galaxies bound together by gravity; smaller collections of galaxies are simply called
groups (groups of galaxies with more than a few dozen members)
SUPERCLUSTERS consists of many clusters of galaxies, groups of galaxies, and
individual galaxies and are the largest known structures in the universe
LOCAL SUPERCLUSTER the Supercluster of galaxies to which the Local Group
UNIVERSE the sum total of all energy and matter
BIG BANG The event that gave birth to the universe
LIGHTYEARS the distance that light can travel in 1-year, about 9.46 trillion km/6
trillion miles !ONE LIGHTYEAR
OBSERVABLE UNIVERSE the portion of the entire universe that we can potentially
observe (consists only of objects that lie within 14 billion light-years)
ASTRONOMICAL UNIT (au) equivalent to about 150 million km
ECLIPTIC PLANE the plane of the Earth’s orbit around the Sun
AXIS TILT 23.5 degrees in relation to ecliptic plane
Chapter 2 Discovering the Universe for Yourself
CONSTELLATION a region in the sky; 88 official constellations cover the celestial
CELESTIAL SPHERE the imaginary sphere on which objects in the sky appear to
reside when observed from Earth – shows us how stars appear to be arranged in the sky
North Celestial Pole the point directly over Earth’s North Pole
South Celestial Pole The point directly over Earth’s South Pole
Celestial Equator a projection of Earth’s equator into space, makes a
complete circle around the celestial sphere

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Ecliptic the path the Sun follows as it appears to circle around the
celestial sphere once each year
ECLIPTIC PLANE the plane of the Earth’s orbit around the Sun
LOCAL SKY the sky as seen from wherever you happen to be standing
HORIZON the boundary between the Earth and the sky
ZENITH the point directly overhead (has an altitude of 90degrees BUT NO
DIRECTION because it is straight overhead)
MERIDAN an imaginary half circle stretching from the horizon due south, through the
zenith, to the horizon due north
AZIMUTH (DIRECTION) direction along the horizon (used to pinpoint the position of
any object in the local sky) " N E S W
ALTITUDE (above the horizon) ANGLUAL distance between the horizon and the
object in the sky
ANGULAR SIZE/DISTANCE a measure of the angle formed by extending imaginary
lines outward from our eyes to span an object (or between two objects)
- SIZE angle of an object that it appears to span in your field of view
- DISTANCE the angle that appears to separate a pair of objects
CIRCUMPOLAR stars that always remain above the horizon for a particular latitude
CHAPTER 4 – Making Sense of the Universe
SPEED the rate at which an object moves. Its units are distance divided by time, such
as m/s or 100 km/hr (s=d/t)
VELOCITY the combination of speed and direction of motion; it can be stated as speed
in a particular direction, such as 100km/hr due north
ACCELERATIONthe rate at which an object’s velocity changes. Its standard units are
m/s! (change in velocity speed/direction/both)
ACCELERATION OF GRAVITY the acceleration of a falling object (abbreviated
MOMENTUM the product of an object’s mass and velocity
FORCE anything that can cause a change in momentum (ONLY way to change
NET FORCE overall force to which an object responds; the net force is equal to the
rate of change in the object’s momentum (NF = MASS*ACCELEATION)
ANGULAR MOMENTUM momentum attributable to rotation of revolution (circular
movements); the angular momentum of an object moving in a circle of radius r is the
product m*V*r
TORQUEa twisting force that can cause a change in an object’s angular momentum
MASS amount of matter in your body
WEIGHT the net force that an object applied to its surroundings (humans on Earth –
weight = mass*acceleration of gravity)
FREE FALL falling without any resistance to slow you down
WEIGHTLESS a weight of zero, occurs during free-fall

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NEWTON’S LAWS OF MOTION three basic laws that describe how objects respond
to forces
LAW OF CONSERVATION OF MOMENTUM the principle that, in the absence of
net force, the total momentum of a system remains constant
absence of net torque (twisting force), the total angular momentum of a system remains
LAW OF CONSERVATION ENERGY the principle that energy (including mass-
energy) can be neither created nor destroyed, but can only change form one form to
UNIVERSAL LAW OF GRAVITATIONlaw expressing the force of gravity between
two objects
1) every mass attracts every other mass through the force of gravity
2) the strength of the gravitational force attracting any two objects is
DIRECTLY PROPORTIONAL to the product of their masses (e.g. doubling
the mass of one object doubles the force of gravity between the two objects)
3) the strength of gravity between two objects decreases with the SQUARE of
the distance between their centers (e.g. doubling the distance between two
objects weakens the force of gravity by a factor of 2 ! or 4)
KEPLER’S LAWS OF PLANETARY MOTION three laws that describe the motion of
the planets around the sun
1) the orbit of each planet about the Sun is an ellipse with the Sun at one
2) as a planet moves around its orbit, it sweeps out equal areas in equal
times a planet moves faster when it is closer to the Sun than when it is
farther from the Sun in its orbit
3) the square of a planet’s orbital period is proportional to the cube of its
average distance from the Sun more distant planets move more slowly in
their orbits
BOUND ORBITS orbits in which an object goes around another object over and over
again (ellipse and circles)
UNBOUND ORBITS paths that bring an object close to another object just once
(hyperbolas and parabolas)
CENTER OF MASS the point at which two or more orbiting objects would balance if
they were somehow connected; it is the point around which the orbiting objects actually
orbit the mass lies closer to the more massive object (sun in the case of the sun and
CHAPTER 5 – Light and Matter
POWER rate of energy flow
WATTS the standard units of power
JOULES the standard units of energy
SPECTRUM (electromagnetic spectrum) the complete spectrum of light (radio waves,
infrared, ultraviolet, visible light, x-rays, gamma rays)
4 Ways Light Can Interact With Matter:
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