The Cosmic Perspective Ch 1-3


the scientific study of the universe; It includes the observation and interpretation of celestial bodies and phenomena

retrograde motion

the apparent westward motion of the planets with respect to the stars

astronomical unit (AU)

average distance from the Earth to the sun; 1.5 � 10?, or million kilometers


has a semi-major and major axis and two foci.


the spinning of a body, such as earth, about its axis


the motion of one body about another, as Earth about the sun


a slow motion of Earth's axis that traces out a cone over a period of 26,000 years


the point in the orbit of a planet where it is closest to the sun


the place in the orbit of a planet where the planet is farthest from the sun


the point at which the moon is closest to the Earth


the point where the moon is farthest from Earth

phases of the moon

the progression of changes in the moon's appearance during the month. In order- New moon, waxing crescent, 1st quarter, waxing gibbous, full moon, waning gibbous, 3rd quarter, waxing crescent.


A cloud of dust, gas or both in space. Where star clusters are formed.


A small, irregular shaped body formed by colliding matter.

Geocentric Model

the model where the planets, sun, and moon orbit Earth

Heliocentric Model

the model where Earth and other planets orbit the sun

Claudius Ptolemy

About 140 AD in the Alexandria
� Fit universe to a mathematical model
� Geocentric
� Uniform circular motion
� Epicycles and deferents
� Very accurately predicted planet positions (at first)

Nicolaus Copernicus

� Proposed a heliocentric universe
� Motivated to reinstate uniform circular motion in its purest form
� Retrograde motion was a natural result of the Earth's motion
� Needed more epicycles than Ptolemy
� Predictions were no better than the Alfonsine Tabl

Tycho Brahe

� Decades of accurate observations
� No parallax for the nova of 1572
� Placed the nova past the Moon
� De Stella Nova, made him famous in educated circles
� No parallax for stars
� Favored the Herakleides cosmology

Kepler law #1

all planets orbit sun in ellipse

Kepler law #2

when a planet is closer to the sun in its orbit, it moves faster

Kepler law #3

p�=a� when p is an orbital period in yrs, and a is the avg dist. from the sun in AU

Galileo Galilei

-discovered how bodies fell
-first to use telescope for scientific purposes
-discovered moons are imperfect
-discovered Jupiter's moons
-claimed discovery of sun-spots (actually Jesuits)
-work resulted in Decree of 1616, no one allowed to teach Copernican

Sir Isaac Newton

-created three laws of motion
-invented integral calc

29 � days

time from new moon --> new moon

27 1/3 days

days it takes moons orbit around earth

synodic month

new moon --> new moon is called

sidereal month

earth, moon, and star are all aligned


region where sunlight is completely blocked


region where sunlight is partially blocked


a meteoroid that actually reaches earth's surface

Lunar Eclipse

the blocking of sunlight to the moon that occurs when Earth is directly between the sun and the moon

Solar Eclipse

occurs when the Moon passes directly between the Sun and Earth and casts a shadow over part of Earth


the total sum of all matter and energy


large, glowing ball of gas that generates heat and light via nuclear fusion


In order for an object to be considered a planet it must orbit a star (but neither be a star nor a moon), be massive enough to give it a nearly round shape, and clear the neighborhood around its orbit. If an object meets the first two criteria, but not th


object that orbits planet


a relatively small and rocky object that orbits a star


a small, icy object that orbits a star

small solar system body

an asteroid, comet, or other object that orbits a star, but doesn't qualify as a planet or dwarf planet

solar system

a star (or sometimes more than one star) and all the objects that orbit it in its gravitational field.

star system

a star, and any planets or other materials that orbit it


A galaxy is a huge collection of stars bound together by gravity at a common center

galaxy cluster

a collection of galaxies bound together by gravity (called a group if small collection, and a cluster if large collection)


a gigantic region of space where many individual galaxies are packed closely

observable universe

the portion of the entire universe that can be seen from earth on principle- 14 billion light years in all directions

Planets in order away from the sun

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and (not really per se) Pluto

Edwin Hubble

1.) Every galaxy is moving away from us. 2.) The further the galaxy, the faster it is moving


a region of the sky with defined borders


the point above the observer that is directly opposite the nadir on the imaginary sphere against which celestial bodies appear to be projected


imaginary line drawn from the horizon due north to due south


direction of a celestial object, degrees clockwise from due North, and it's altitude above the horizon

Summer Solstice

June 21

Winter Solstice

December 22, when the sun is at its southernmost point

Spring Equinox

March 21

Fall Equinox

September 22

lunar eclipse

earth lies between sun and moon

solar eclipse

moon lies between sun and the earth

nodes of orbit

where moon crosses elliptic plane

conditions for ellipse

1.) Moon must be fill
2.) Nodes must be aligned

Types of lunar eclipes

1.) total- moon passes through umbra
2.) partial- part of moon passes through umbra
3.) penumbral- moon passes through prenumbra

Types of solar eclipses

1.) total- occurs in area that falls in the moon's umbral shadow
2.) partial- occurs in the area falling the the penumbral shadow
3.) annular- occurs when the umbral shadow doesn't reach the earth, where the umbral shadow would've hit

stellar paralax

when stars shift back and forth against back-ground of distant stars

metonic cycle

19 year cycle on which the dates of the lunar cycle repeat, Named for Greek astronomer Meton

light year

distance it takes light to travel in one year (10 trillion KM)

tilt of earth's axis perpendicular to elliptic plane

23.5 degrees

order of magnitude estimate

estimates to nearest power of 10

saros cycle

occurs every 18 years and 11 1/3 days. combination of changing eclipse seasons and lunar cycles.


� Earth a sphere
� Sun, Moon and planets on wheels
� The music of the spheres
� Only the master could hear the music


-first to suggest earth moved
-believed earth moved around central fire


heliocentric model


planets orbit sun, sun orbits earth (couldn't see stellar parallax)


-Taught observation is useless
-heavens were perfect, planets spheres, motion was uniform


-taught earth didn't move
-heaven and earth different spheres


-geocentric solar system
-made accurate predictions of planets for some time

5 Obstacles to Astronomy Copernican Revolution

-Separate earth and heavens
-geocentric dogma
-dogma of circular motion
-science w/o math
-misunderstanding of motion

Copernican Revolution

Heliocentric model

Newton's Three Laws

1. A object in motion tend to stay in motion unless acted on by another force.
3. Every action has a equal and opposite reaction


� Actually paid for the publication of the Principia, Newton's book on physics which contained
the law of gravity.
� Showed that the orbit the comet of 1682 was the same as the orbit of the comets of 1531 &

small angle formula

angular size= physical size(360/2?distance)