midterm astro

Milkyway contains ___ stars

100 billion

Local Group

about 40 galaxies in galaxy cluster

Superclusters

clusters of galaxy clusters

1 AU

earth's average distance from sun

Light Year

distance light can travel in one year (9.46 tril km)

Observable Universe

14 billion light years

Big Bang

happened 14 bill years ago, avg. distance between galaxies increasing over time

Star Birth

gravity compresses material in cloud, center becomes hot/dense, undergoes nuclear fusion

Supernovae

massive stars dying in huge explosions

Elements in earliest universe

Hydrogen and Helium

Earth's Rotation

Rotates daily around axis, from west to east

Sun and Stars rise in the ___ , set in the ___

east, west

Ecliptic plane

flat plane defined by Earths orbit

Created sun centered solar system idea

Copernicus

Zodiac

constellations across ecliptic

Precession

gradual wobble that alters orientation of Earth's axis in space (every 26,000 years)

Zenith

point directly overhead

Meridian

half circle from north to south through the zenith

Angular size of moon

.5 degrees

Synchronous rotation

moon rotates on its axis the same amount of time it takes for it to orbit earth

New Moon

occurs when moon is between the sun and earth

Lunar Eclipse

moon must be full; earth lies between sun and moon

Solar Eclipse

moon must be new; moon lies between sun and earth

The altitude of celestial pole in sky is equal to

your latitude

Reason for seasons

tilt of Earth's axis causes sunlight to fall differently on Earth at different times of year

Lundar Phase

29.5 days

Apparent Retrograde Motion

apparent motion of a planet moving westward through the zodiac

Stellar Parallax

apparent shift in position of a nearby star based on position of orbit (doesn't happen if object is far away)

Reason for Greeks rejecting explanation for planetary motion

they couldn't detect parallax

Solar Calendar

what we use, synchronous with seasons

Geocentric model

Greek; placed Earth at center of universe

Ptolemaic Model

each planed moved around Earth on a small circle that turned about a larger one

Plato

heavenly motion must be in perfect circles

Kepler

discovered planetary orbits are ellipses

Keplers 1st Law of Planetary Motion

orbit of each planet around the sun is an ellipse with the sun at one focus (planets distance from sun varies during orbit)

Keplers 2nd Law of Planetary Motion

As a planet moves around its orbit, it sweeps out equal areas in equal times (planet travels faster nearer to the sun, slower further from sun)

Keplers 3rd Law of Planetary Motion

more distant planets orbit the sun at slower avg. speeds p^2=a^3

Tycho

observed first nova, saw it was further than moon

Objections to Copernicus' view of sun centered system

objects would fall away if Earth was moving, noncircular orbits meant heavens weren't perfect, no one could detect parallax

Aristotle

argued Earth centered universe

Speed

how far object will go in certain amt. of time

Velocity

speed and direction

Acceleration

change in velocity

Acceleration of Gravity (g)

acceleration of falling object, 9.8 m/s^2

Momentum

mass x velocity

Mass

amount of matter

Weight

mass x force; no gravity = no weight

Newton's 1st Law of Motion

an object moves at constant velocity if there is no net force acting upon it

Newton's 2nd Law of Motion

force = rate of change in momentum

F = M x A

Newton's 3rd Law of Motion

for any force there is always an equal an opposite reaction force

Conservation of Momentum

if there are no external forces, the total momentum of 2 interacting objects cannot change

Conservation of Angular Momentum

if there is no external torque, the total momentum of interacting objects cannot change

Angular momentum

mass x velocity x radius

Conservation of Energy

energy cannot appear/disappear out of nowhere, can only lose/gain energy by exchanging

Kinetic Energy

energy of motion, 1/2mv^2

Radiative Energy

energy carried by light

Potential energy

stored energy, gpe=m x g x h

Joule

standard unit of energy

Mass-Energy

E=MC^2

e = Amt of potential energy c = speed of light m = mass

Thermal energy

measures total kinetic energy of particles

Temperature

measures the average kinetic energy of particles in object

Universal Law of Gravitation

a) every mass attracts other mass through force of gravity

b) strength of gravitational force attracting any 2 objects is directly proportional to the product of their masses

c) inverse square law- strength of gravity between 2 objects decreases with the square of the distance between their centers

formula = F = G(m1m2/d^2)

Escape Velocity

amount of velocity required to escape earth's orbit (40,000 km/hr)

Moon's Tidal Force

difference in gravitational attraction from earth and moon on each side of the earth creates this

Power

rate of energy flow (watts)

Watt

1 joule/sec

White

colors in spectrum are equally mixed

Black

no light reflected

Diffraction Grating

glass etched with many closely spaced lines, produce spectrum

Speed (light)

wavelength x frequency

Frequency

cycles per second (Hz)

Light is an Electromagnetic wave

traveling vibrations of both electric and magnetic fields

Photon

light behaves as a wave and particle

Infrared

light with wavelengths longer than red light

Radiowaves

longest wavelength

Microwaves

light falling between infrared and radiowaves

UV rays

light with wavelengths shorter than blue

X Rays

shorter than UV rays

Gamma rays

shortest rays

Emission

light bulb emits visible light

Absorption

when you place your hand near bulb, your hand absorbs some light, then warms hand

Transmission

glass/air, forms of matter, can allow light to pass through

Reflection/Scattering

light can bounce off matter, either all in same direction, or random

Visible Light

what we can see, 400 nm to 700 nm

Atomic Number

number of protons in nucleus

Atomic Mass

combined number of protons and neutrons

Sublimation

solid to gas

Evaporation

liquid to gas

Ionization

stripping electrons from atoms

Pressure

force per unit area pushing on objects surface

Intensity

amount of light at each wavelength

Spectroscopy

process of obtaining a spectrum and reading the information it contains

Continuous Spectrum

broad range of wavelengths without interruption (rainbow)

Emission Line Spectrum

light is only emitted at specific wavelengths (bright lines against a black background)

Absorption Line Spectrum

specific light wavelengths are absorbed (dark lines over rainbow background)