Astronomy: Ch. 1-3

Front 1

Astronomy

Back 1

The study of the objects that lie beyond our planet Earth, and of the processes by which these objects interact with one another

Front 2

Historical Science

Back 2

What we observe has already happened in the universe and we can do nothing to change it

Front 3

Light Year

Back 3

The distance that light travels in one year

Front 4

Planet

Back 4

A body of significant size that orbits a star and does not produce its own light

Front 5

Brown Dwarfs

Back 5

A class of objects intermediate between stars and planets; are failed stars- balls of hot gas that do not have what it takes to keep producing significant amounts of light

Front 6

Galaxy

Back 6

Group of stars

Front 7

Dark Matter

Back 7

Nonluminous mass, whose presence can be inferred only because of its gravitational influence on luminous matter; composition is not known

Front 8

Universe

Back 8

Everything that exists that is accessible to our observations

Front 9

Quasars

Back 9

Brilliant centers of galaxies, glowing with the light of some extraordinarily energetic process

Front 10

Geocentric

Back 10

Earth-centered

Front 11

Zenith

Back 11

The top of the dome that is directly above your head

Front 12

Horizon

Back 12

The line where the dome meets the Earth

Front 13

Celestial Sphere

Back 13

Apparent sphere of the sky; a sphere of large radius centered on the observer. Directions of objects in the sky can be denoted by their position on the celestial sphere

Front 14

Axis

Back 14

The imaginary stick that our planet rotates on

Front 15

North Celestial Pole & South Celestial Pole

Back 15

The points where the axis meets the celestial sphere

Front 16

Celestial Equator

Back 16

A great circle on the celestial sphere 90 degrees form the celestial poles; where the celestial sphere intersects the plane of the Earth's equator

Front 17

North Circumpolar Zone

Back 17

The area within 38 degrees of the North pole

Front 18

South Circumpolar Zone

Back 18

The area within 38 degrees of the South Pole

Front 19

Ecliptic

Back 19

The path the Sun appears to take around the celestial sphere each year

Front 20

Constellation

Back 20

One of 88 sectors into which astronomers divide the celestial sphere; many constellations are named after a prominent group of stars within them that represents a person, animal, or legendary creature form ancient mythology

Front 21

Zodiac

Back 21

A belt around the sky about 18 degrees wide centered on the ecliptic

Front 22

Cosmology

Back 22

Our concept of the cosmos (its basic structure and origin)

Front 23

Parallax

Back 23

The apparent shift in the direction of an object as a result of the motion of the observer

Front 24

Stellar Parallax

Back 24

The shift in the apparent direction of a star due to the Earth's orbital motion

Front 25

Magnitude

Back 25

A system for measuring the amount of light flux received from a star or other luminous object; the higher the magnitude, the less radiation we receive from the object

Front 26

Retrograde Motion

Back 26

An apparent westward motion of a planet on the celestial sphere or with respect to the stars

Front 27

Epicycle

Back 27

A circular orbit of a body in the Ptolemaic system, the center of which revolves about another circle

Front 28

Ellipse

Back 28

A flattened circle

Front 29

Focus

Back 29

One of two fixed points inside an ellipse from which the sum of the distances to any point on the ellipse is a constant

Front 30

Major Axis

Back 30

The widest diameter of an ellipse

Front 31

Semimajor Axis

Back 31

Half the distance of the major axis; usually used to specify the size of the ellipse

Front 32

Eccentricity

Back 32

The ratio of the distance between the foci to the length of the major axis

Front 33

Kepler's First Law

Back 33

Each planet moves about hte Sun in an orbit that is an ellipse, with the Sun at one focus of the ellipse

Front 34

Kepler's Second Law

Back 34

The straight line joining a planet and the Sun sweeps out equal areas in space in equal intervals of time

Front 35

Kepler's Third Law

Back 35

The squares of the planets' periods of revolution are in direct proportion to the cubes of the semimajor axes of their orbits

Front 36

Newton's First Law

Back 36

Every body continues doing what it is already doing- being in a state of rest or moving uniformly in a straight line- unless it is compelled to change by an outside force

Front 37

Newton's Second Law

Back 37

The change of motion of a body is proportional to the force actin on it and is made in the direction in which that force is acting

Front 38

Newton's Third Law

Back 38

To every action there is an equal and opposite reaction (or the mutual actions of two bodies upon each other are always equal and act in opposite directions)

Front 39

Conservation of Angular Momentum

Back 39

The law that the total amount of angular momentum in a system remains the same (in the absence of any force not directed toward or away from the point or axis about which the angular momentum is conserved

Front 40

Angular Momentum

Back 40

A measure of the momentum of an object as it rotates or revolves about some fixed point

Front 41

Gravity

Back 41

The mutual attraction of material bodies or particles

Front 42

Orbit

Back 42

The path of an object through space

Front 43

Perihelion

Back 43

The place in the orbit of an object revolving about the Sun where it is closest to the Sun's center

Front 44

Aphelion

Back 44

Point in its orbit where an Earth satellite is farthest from the Earth

Front 45

Perigee

Back 45

The place in the orbit of an Earth satellite where it is closest to the center of the Earth

Front 46

Apogee

Back 46

Point in its orbit where an Earth satellite is farthest from the Earth

Front 47

Asteroid Belt

Back 47

The great majority of asteroids in our solar system that lie between 2.2 and 3.3 AU

Front 48

Circular Satellite Velocity

Back 48

The critical speed that a revolving body must have in order to follow a circular orbit

Front 49

Escape Velocity

Back 49

The velocity a body must achieve to break away from the gravity of another body and never return to it

Front 50

Great Circle

Back 50

Any circle on the surface of sphere whose center is at the center of the sphere

Front 51

Declination

Back 51

Angular distance north or south of the celestial equator

Front 52

Right Ascension

Back 52

A coordinate for measuring the east-west positions of celestial bodies; the angle measured eastward along the celestial equator from the vernal equinox to the hour circle passing through a body

Front 53

Solar Day

Back 53

The rotation period of the Earth with respect to the Sun

Front 54

Sidereal Day

Back 54

Period of the revolution of one body about another measured with respect to the stars

Front 55

Apparent Solar Time

Back 55

Time as measured by the position of the Sun in the sky (the time that would be indicated by a sundial)

Front 56

Mean Solar Time

Back 56

Based on the average value of the solar day over the course of the year; contains exactly 24 hours

Front 57

Phases

Back 57

A particular point in the time of a cycle or any distinct time period in a sequence of events

Front 58

Eclipse

Back 58

Occurs whenever any part of either the Earth or the Moon enters the shadow of the other

Front 59

Solar Eclipse

Back 59

When the sun is at least partially covered by the Moon

Front 60

Lunar Eclipse

Back 60

When the Moon passes into the shadow of the Earth