Astronomy 103 Midterm

Front 1

Newton's first law of motion

Back 1

Inertia

= Velocity of an object only changes when forces act on it

Front 2

force

Back 2

something that can change an object's velocity

Front 3

speed of light

Back 3

2.998 x 10⁵ km/sec

~300,000 km/sec

Front 4

light-year

Back 4

9.46 x 10^12 km

Front 5

parsec

Back 5

distance to nearest star

3.261633 light years

Front 6

The Four Fundamental Forces

Back 6

strong force
weak force
electromagnetic force
gravitational force

Front 7

strong force

Back 7

holds together nuclei of atoms

100 times stronger than electromagnetic force that repels protons

1 billion times stronger than weak force

three colors combine to make neutral combinations

"gluon" particle carries strong force

Front 8

weak force

Back 8

causes one type of larger-mass particle to decay into another lower-mass kind of particle

a billion times weaker than strong force

10 million times weaker than electromagnetic force

W and Z carrier particles

Front 9

electromagnetic force

Back 9

opposites attract, likes repel

photon

100 times weaker than strong force
10 million times stronger than weak force

Front 10

ecliptic

Back 10

line that sun traces across the celestial sphere

Front 11

celestial poles

Back 11

areas of sky right above earth's rotational poles - stars here do not move

Front 12

celestial equator

Back 12

line of sky along earth's equator

Front 13

vernal equinox

Back 13

march 21

Front 14

autumnal equinox

Back 14

sept 23

Front 15

solstices

Back 15

june 21
dec 21

Front 16

arctic circle

Back 16

north of 66.5 degrees N

sun does not rise during parts of the year

Front 17

antarctic circle

Back 17

south of 66.5 degrees S

sun does not rise during parts of year

Front 18

tropic of cancer

Back 18

23.5 degrees N

northern limit of "tropical" latitudes.

sun is in the zodiac constellation Cancer at this latitude during summer solstice

Front 19

tropic of capricorn

Back 19

23.5 degrees S

southern limit of "tropical" latitudes

sun is in zodiac constellation capricorn during winter solstice

Front 20

precession

Back 20

"wobbling" of spinning earth (think of a top)

happens very slowly - a single "wobble" takes 26,000 years

Front 21

ante meridian

Back 21

a.m.

Front 22

post meridian

Back 22

p.m.

Front 23

sidereal day

Back 23

one day as measured by how long it takes a star to return to the same point in the sky

23 hours, 56 minutes, 4.0905 seconds

Front 24

leap second

Back 24

adjustment of atomic clocks by a second every year or two to compensate for gradual slowing of earth's orbit

Front 25

tidal friction

Back 25

moon exerts gravity on ocean tides to make them more stationary than the earth's rotation generally -- tides 'run into' sides of continents and create friction with respect to rotation

this is gradually slowing the orbit of the earth -- 400 million years ago earth had 22 hours in a day, 400 days in a year.

Front 26

solar eclipse

Back 26

moon passes between sun and earth, shadow of moon falls on earth

can only occur at new moon

Front 27

lunar eclipse

Back 27

shadow of earth falls on moon

can only occur at full moon

Front 28

umbra

Back 28

regions during an eclipse where light is blocked completely

Front 29

penumbra

Back 29

regions during an eclipse where light is only partially blocked

Front 30

annular eclipse

Back 30

moon is far enough away from earth at time of solar eclipse that it appears smaller than sun and one can see sun as a 'ring' around the moon during eclipse

Front 31

parallax

Back 31

shift in star's apparent position resulting from earth's motion round the sun

usually VERY SMALL

Front 32

angular size

Back 32

how big an object *looks*

measured by drawing (imaginary) lines to each side of object and then measuring the angle

linear size = distance x angular size/57.3 degrees

Front 33

retrograde motion

Back 33

planets (like mars) appear to move backward in sky for a time because earth is orbiting faster than other planet

Front 34

Kepler's first law

Back 34

Planets move in elliptical orbits with the sun at one focus of the ellipse

Front 35

Kepler's second law

Back 35

orbital speed of a planet varies such that a line joining the sun and the planet will sweep over equal areas in equal time

Front 36

Kepler's third law

Back 36

the amount of time a planet takes to orbit the sun (P) is related to its orbit's size (a).

P^2 years= a^3 AU

Front 37

mass

Back 37

amount of matter an object contains

Front 38

weight

Back 38

net force acting on an object (generally in a constant manner)

Front 39

acceleration

Back 39

change in velocity / change in time

Front 40

velocity

Back 40

directional speed

Front 41

Newton's second law of motion

Back 41

the force (F) acting on an object equals the product of its acceleration (a) and its mass (m).

F = m x a

Front 42

Newton's third law of motion

Back 42

action-reaction

When two bodies interact, they create equal and opposite forces on each other

Front 43

Newton's Universal Law of Gravitation

Back 43

Every mass exerts a force on every other mass.

This force (F) is proportional to the product of the masses (M x m) divided by the square of the distances between them.

F = G x M x m / d^2

Front 44

newton

Back 44

kg x m / sec^2

Front 45

surface gravity

Back 45

Acceleration (g) caused by gravity on a planet's surface. Mass of falling object does not matter, acceleration will be the same.

g = G x M / R^2

Front 46

centripetal force

Back 46

Applied to any object moving in a circle or curve. Centripetal force (F) on an object with mass (m) moving with a velocity (V) at distance (d) from the cetner fo the circle...

F = m x V^2 / d

Mass of an orbital center from the speed and distance of an object orbiting it...

M = d x V^2 / G

Front 47

Newton's modification of Kepler's Third Law

Back 47

Sum of masses of two orbiting bodies (M(a) and M(b)) obey the following law (where masses are in units of the mass of the sun)...

M(a) + M(b) = a^3 AU / P^2 years

Front 48

orbital velocity

Back 48

object in scircular orbit must have velocity of...

V = (G x M / R)^(1/2)

Front 49

escape velocity

Back 49

velocity needed to escape from the gravitational pull of a body

V = (2GM/R)^(1/2)

Front 50

tidal bulges

Back 50

differential gravitational forces pull water into bulges on side of earth facing the moon as well as on side directly opposite

Front 51

kinetic energy

Back 51

energy of an object in motion

E = 1/2 x m x V^2

E in joules
m in kg
V in m/sec

Front 52

gravitational potential energy

Back 52

E = (-G x m x M)/d

E in joules
m, M in kg
d in m

Front 53

Angular momentum

Back 53

inertia applied to rotation, unless acted upon by an outside rotational force (torque)

If a mass (m) is moving around a rotational axis at a distance (r) with a velocity (V), then it's angular momentum...

= m x V x R

Front 54

"quantized" energy

Back 54

comes in discrete packets

e.g., you can have 1, 2, or 3 photons, but not 1/2 or 1.7

Front 55

inverse-square law

Back 55

brightness = total light output / (4πd^2)

Front 56

emission

Back 56

electron drops from a higher to a lower orbital and gives off energy of a specific amount as an electromagnetic wave

Front 57

absorption

Back 57

light's energy is stored in an atom as energy, moving an electron to a higher orbital

Absorption can ionize an atom if the energy given to the electron is great enough that it escapes the orbit of the atom completely.

Front 58

wavelength

Back 58

spacing between wave crests according to wave interpretation of light

Usually represented by Greek letter λ.

Front 59

Frequency

Back 59

number of wave crests that pass a point in 1 second

This unit is hertz (Hz)

Usually denoted by Greek letter nu: ν

Front 60

relation of frequency to wavelength

Back 60

by definition...

λ x ν = c

Front 61

energy carried by photons

Back 61

A photon carries an amount of energy proportional to its frequency and inversely proportional to its wavelength

E = (h x c) / λ

h = Planck's constant

Front 62

blackbody

Back 62

an object that absorbs all radiation falling on it

Front 63

Wien's Law

Back 63

Hotter bodies radiate more strongly at shorter wavelengths

Front 64

Stefan-Boltzmann Law

Back 64

The luminosity of a hot body rises rapidly with temperature.

Luminosity is proportional to temp (in degrees Kelvin) to the fourth power

luminosity ~ T^4

Front 65

continuous spectrum

Back 65

atoms emit light of all visible wavelengths

Front 66

emission-line spectrum

Back 66

produced by hot, low-density gas

molecules well-separated so atoms can become excited without bumping into each other too much, thus they produce specific emissions when they drop back down

Front 67

absorption-line spectrum

Back 67

light from a hot, dense body (like sun) passes through cooler gas between it and observer

Front 68

radial velocity

Back 68

speed of an object along one line of sight:

V = (Δλ / λ) x c

This uses Doppler shift, where λ is the wavelength originally generated

Front 69

CCDs

Back 69

charge-coupled devices

Superior, reusable alternative to film. Gets about 75% efficiency of photon recording as opposed to film's ~10%

Front 70

collecting area

Back 70

the bigger a telescope's collecting area, the more photons it can gather

The area of a circular collector of diameter D is...

Collecting area = (π/4) x D^2

Front 71

refraction

Back 71

transparent lenses bend electromagnetic waves including light

Front 72

dispersion

Back 72

different wavelengths of light refracted at different amounts, like white light passing through a prism

Front 73

diffraction

Back 73

when waves pass thru an opening, they are bent at the edges of the opening

relevant for telescope-making

Front 74

calculating resolution of a telescope

Back 74

D(cm) > 0.02λ(nm) / α (arcsec)

or

α > 0.02λ / D

Front 75

interferometer

Back 75

combined set of telescopes that function like one big telescope