Astronomy 101 - Exam 1 Study Terms

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Astronomical Unit

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60 Terms

1

Astronomical Unit

the average distance between the sun and the earth

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2

Light year

the distance that light travels in a year

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3

the celestial sphere

An imaginary sphere (dome) that models the projection of objects in the sky

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4

Horizon

Line where the dome meets the earth

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5

Zenith

Top of the dome, above your head.

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6

Ecliptic Tilt

on the celestial sphere and is the apparent path of the sun over the course of the year.

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7

Tropical Year

Based on the seasons

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8

Sidereal year

Based on the earth’s orbit around the sun. (the true year)

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9

Zodiac

the 12 constellations the sun moves through during the year.

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10

Constellation

Bright stars that are grouped together

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11

Eratosthenes

First person to get a fairly accurate determination of the Earth’s diameter.

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12

Hipparchus

Discovered the position in the sky of the north celestial pole had altered over the previous century → precession “slow shift” of Earth’s axis.

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13

Claudius Ptolemy

proposed a model for the solar system to explain retrograde motions of the planets

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14

Epicycles

a small circle whose center moves around the circumference of a larger one.

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15

Geocentric model

earth lays at the center of the universe

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16

Aristotle

proposed geocentric model

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17

Aristarchus of Samos

proposed that planets revolved around the sun but was ignored because of Aristotle’s following

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18

Heliocentric Model

Planets orbit in circles around the sun

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19

Galileo

built and used the telescope

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20

Kepler’s first law ( The law of orbits )

Planet’s move around the sun in elliptical orbits (ellipses): ea. planets orbit about the sun is an ellipse.

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21

Ellipse

Oval shaped path that celestial objects follow as they orbit the sun

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22

Eccentricity

The determination of how oval an ellipse is. → length of the major axis

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23

Kepler’s 2nd law

A planet moves faster when closer to it’s sun and slower when it’s farther

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24

Kepler’s 3rd Law

the farther a planet is from the sun, the longer it’s orbital period.

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25

Major axis

Diameter of the ellipse, stretching from one end to the other.

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26

Semi major axis

Half of the major axis

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27

Isaac newton

Father of the laws of motion

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28

Angular momentum

The spinning power of an object (spinning or moving in a circle) The faster or heavier the more angular momentum.

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29

Gravity

general force of attraction

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30

Gravitational force

attractive forces between masses.

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31

Aphelion

Farthest distance from sun and moves slowly

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32

Perihelion

Closest distance to sun and moves fast

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33

Escape speed

Speed needed to move away from Earth forever

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34

refraction

the bending of light passing through air or water

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35

solar day

earth’s rotation relative to the sun

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36

sidereal day

earth’s rotation relative to distant stars

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37

synchronous rotation:

rotates once on its axis while simultaneously orbiting earth once. → keeps the same face toward earth

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38

sidereal month

time it takes moon to make a full 360 around earth

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39

synodic month

time it takes moon to complete cycle of phases

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40

Giant Impact Theory

proposes that the moon was formed from the debris of a massive collision between earth and another celestial body.

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41

Solar Eclipse

Sun covered by moon

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42

Lunar Eclipse

Moon dimming.

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43

Annular Eclipse

ring of light

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44

Total Solar Eclipse

Sun completely hidden

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45

Penumbra

sun partially visible

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46

umbra

sun completely blocked.

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47

Electromagnetic Radiation

transmission of energy through space

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48

Mechanical Wave

wave that needs a medium to travel through (ie. sound and water waves)

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49

Electromagnetic Wave (EM)

wave that travels through vacuum, without medium (ie. radio, light, microwaves)

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50

Photon

tiny packets of energy that makeup light

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51

Inverse Square Law for Light Propagation

light becomes weaker the further it travels from its source

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52

Electromagnetic Spectrum

range of EM radiation

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53

Blackbody Radiation

type of light emitted by an object and absorbs light

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54

Wien’s law

as an object gets hotter, its peak wavelength become smaller

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55

Stefan-Boltzmann Law

as the temperature of an object increases, it radiates more energy.

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56

Spectrometer

device to measure and analyze the properties of light such wavelength and energy

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57

Atom

building block of all matter

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58

Doppler Effect

wavelength of light shortens toward source, lengthens away from it.

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59

Reflector

telescope using mirrors

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60

Refractor

telescope using lens

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