Astronomy Midterm

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a ____ is a collection of hundreds and billions of stars.

galaxy

the light year is a unit of ____

distance

rotation is the term used to describe the motion of a body around some ____

axis

to explain the daily and yearly motions of the heavens, ancient astronomers imagined that the sun, moon, and stars, and planets were attached to a rotating ____

celestial sphere /ring

the solar day is measured relative to the sun; the sidereal day is measured relative to the ____

moon

the apparent path of the sun across the sky is known as the ____

ecliptic

on December 21, known as the ____, the sun is at its ____ point on the celestial sphere.

winter solstice / southernmost

declination measures the position of an object north or south of the ____

celestial equator

an arc second is ____ ( give the fraction ) of an arc minute.

1/60th

when the sun, earth, and moon are positioned to form a right angle at earth, the moon is seen in the ____ phase.

waxing / waning gibbous

a ____ eclipse can be seen by about half the earth at once.

lunar

as seen from earth, the sun and the moon have roughly the same ____

size

to measure distances to nearby stars by parallax, a baseline equal to earth's ____ is used.

XXX

the size of an object can be determined, if we know its distance, by measuring its ____

XXX

the radius of ____ was first measure by Eratothenes in 200BC

Earth's

Stonehenge was used as a ____ by the people in the stone age

calendar

accurate records of comets and "guest" stars were kept over many centuries by ____ astrologers.

ancient

the astronomical knowledge of ancient Greece was kept alive and augmented by ____ astronomers

modern

the apparent " backwards" ( westward motion ) of the planets Mars, Jupiter, or Saturn in the sky relative to the stars is known as ____ motion

retrograde

observation, theory, and testing are the cornerstones of the ____

scientific method

the heliocentric model was reinvented by ____

Copernicus

central to the heliocentric model is the assertion that the observed motions of the planets and the sun are the result of ____ motion around he sun.

planetary

Kepler's laws were based on the observational data obtained by ____

research

Kepler discovered that the shape of an orbit is and ____ not a ____ as it had previously been believed

ellipse, circle

Kepler's third law relates to the ____ of the orbital period to the ____ of the semi major axis

XXX

Galileo discovered ____ orbiting Jupiter, the ____ of venus, and the sun's rotation from observation of ____

moon ; atmosphere ; the stars

the modern method of measuring the astronomical unit uses ____ measurements of a planet or asteroid.

AU

Newton's first law states that a moving object will continue to move in a straight line with constant speed unless acted upon by a ____

force

Newton's law of gravity states that the gravitational force between two objects depends on the ____ of their masses and inversely on the ____ of their separation.

sum ; distance

Newton discovered that, in Kepler's third law, the orbital period depends on the semi major axis and on the sum of the ____ of the two objects involved.

masses

A ____ is a glass wedge that disperses light into a spectrum.

prism

blackbody radiation is an example of a ____ spectrum

continuous

Fraunhofer discovered absorption lines in the ____

emission

a continuous spectrum can be produced by a luminous solid, liquid, or ____ gas.

super heated

an absorption spectrum is produced when a ____ gas lies in front of a source of continuous radiation.

emited

light behaves both as a wave and as a ____

particle

the experiment that demonstrated as the ____ caused Einstein to realize that light does not always behave like a wave.

gold foil

protons carry a ____ charge; electrons carry a ____ charge.

positive ; negative

when one or more electrons are stripped from the atom, the atom is said to be ____

ionized

when an electron moves to a higher energy level in an atom it ____ a photon of a specific energy.

absorbs

when an electron moves to a lower energy level in an atom it ____a photon of a specific energy.

expels

the "specific energy" of the photon is exactly equal to the energy ____ between the energy levels involved.

exchanged

changes in a particular molecular vibration states produce spectral features in the ____ part of the electromagnetic spectrum

microwave

changes in the molecular rotational states produce spectral features in the ____ part of the electromagnetic spectrum

visible

high temperature, rotation, and magnetic fields all tend to ____ spectral lines.

distort

a telescope that uses a lens to focus light is called a ____ telescope.

refracting

a telescope that uses a mirror to focus light is called a ____ telescope

reflecting

all large modern telescopes are of the ____ type.

refracting

the light gathering power of a telescope is determined by the ____ of its mirror or lens.

diameter

the angular resolution of a telescope is limited by the ____ of the telescope and the ____ of the radiation being observed

diameter ; amount

the angular resolution of ground based optical telescopes is more seriously limited by earth's ____ than by diffraction.

atmosphere

optical telescope on earth can see angular detail down to about ____ arc second

less than 1

CCDs produce images in ____ form that can be easily transmitted , stored and later processed by computers.

data bytes

Active optics and adaptive optics are both being used to improve the ____ of ground based optical telescopes.

clarity

all radio telescopes are of the ____ design

array

an ____ is two or more telescopes used in tandem to observe the same object, in order to improve angular resolution.

infra-meter

____ , ____ , and ____ astronomy can be done only from above earth;s atmosphere

x - ray, gamma, and ultraviolet

an object with a temperature of 300K would be best observed with an ____ telescope.

infrared

the mirrors in x-ray telescopes are different in design from those in optical instruments because x - rays tend to be ____ , rather than reflected, by solid surfaces.

absorbed

gamma ray telescopes are unable to form ____ of their fields of view

image

the ____ of a wave is the distance between any two adjacent wave crests

wavelength

the ____ of a wave is measured in units of hertz (Hz)

frequency

____ is the ability of a wave to "bend around corners."

diffraction

when a charged particle moves, information about this motion is transmitted through space by means of its changing ____ and____ fields.

positions ; electric

the visible spectrum ranges from ____ to ____ in wavelength

400 ; 700 nm

light with a wavelength of 700 nm is perceived to be ____ in color

red

earth's atmosphere has low opacity for three forms of electromagnetic radiation. they are ____ , ____ , and ____ .

infrared ; radio ; visible

the peak of an object's emitted radiation occurs at a frequency or wavelength determined by the object's ____

temperature

the lowest possible temperature is ____ K .

0

water freezes at ____ K

273

because the sun emits its peak amount of radiation at about 480 nm its temperature must be about ____ K.

6000

two identical objects have temperatures of 1000K and 1200K , respectively. it is observed that one of the objects emits twice as much radiation as the other. which one is it ?

1200K

if an astronomical object is observed to emit x -rays , it is reasonable to assume that its temperature is very ____

high

when an observer and / or object emitting radiation move toward each other, the observer sees the radiation shifted to ____ wavelengths

shorter

the ____ are bodies that orbit the sun between the orbits of Mars and Jupiter

asteroids

the two planets with the highest eccentricity and orbital tilts are ____ and ____

Pluto ; Uranus

the inner planets, mercury, Venus, earth, and mars are known as the ____ planets

inner/rocky

the outer planets jupiter, saturn, uranus and neptune are known a s the ____ planets

outer/gaseous/jovial

the largest and most massive planet in the solar system is ____

Jupiter

asteroids and meteoroids have a ____ composition, in contrast with comets, which have an ____ composition.

rocky ; icy

asteroids are similar in composition to the ____ planets

inner

comets have compositions similar to the ____ moons of the ____ planets

icy ; outer

the mariner 10 spacecraft was sent by ____ ( country ) to photograph the planet ____

USA ; mercury

the U.S. Magellan probe mapped the entire surface of Venus using ____

radar

the viking 1 and viking 2 missions sent orbiters and landers to the planet ____

mars

Jupiter was first visited by the U.S. spacecraft ____

pioneer 10

The U.S. spacecraft ____ is the only probe to have visited each of the giant outer planets.

voyager 2 or new horizon

spacecraft visiting one planet often use a ____ assist to visit another planet

gravity

pencil - beam surveys suggest that the largest structures in space are no larger than ____ Mpc in size.

200

homogeneous means " the same ____ "

throughout

isotropic means " the same in all ____"

directions

together, the assumptions of cosmic homogeneity and isotropy are known as the ____

cosmology

if the universe had an edge, this would violate the assumption of ____

dark matter

if the universe had a center, this would violate the assumption of ____

isotropic principle

a hubble constant of 65 km/s/Mpc gives a maximum age for the universe of ____ billion years

15

____ is slowing the expansion of the universe

gravity

the ____ of the universe determines whether the universe will expand forever

mass

a ____ value for hubble's constant yields an age for the universe incompatible with the oldest globular clusters

large

luminous matter makes up about ____ percent of the critical density

1

by observing distant galaxies, astronomers have determined that the universe was expanding ____ long ago than it is today

faster

the surface of a sphere is a two dimensional example of a ____ curved universe

positive

an open universe has a density ____ the critical value

less than

the temperature of the universe, as measured by the cosmic microwave background, is ____ K

3

comparing the mass density of radiation and matter , we find that, at the present time, ____ dominates

matter

energetically speaking, radiation and matter were equally important approximately ____ years after the big bang

a few thousand

in the process of pair production, two ____ interact to form a particle and an ____

photon ; antiparticle

the temperature necessary to form electrons and positron is about ____

10^9

the temperature necessary to form proton and ____ is about ____ K

neutrons ; 10^13

when the universe was a few minutes old, nuclear fusion produced ____ and ____

helium ; ditrium

after about a million years, ____ had formed in the universe

galaxies

elements heavier than helium were not formed primordially because, as time passed, the density and temperature of the universe____

decreased

the fact that the density of normal matter is so much less than the known density of matter in the universe implies that much of dark matter must be ____

veronic

the cosmic microwave background radiation lat interacted with matter when the universe was about____ times its present size

1150

if the theory of inflation is correct, then dark matter must make up about ____ percent of all matter in the universe.

97

which had density fluctuations first, normal matter or dark matter?

dark matter

we know that density fluctuations in the normal matter component of the early universe must have been very small because otherwise we would see their imprint on the____

cosmic microwave background

hot and cold dark matter differ in the masses of their particles. cold dark matter consists of ____ particles.

heavy

theory predicted tiny fluctuations in the ____ of the microwave background; the ____ satellite found them.

temperature ; koke

the volume surveyed through a long, thin ____ extending deep into space rather than a wide swath through the local universe

cross section

____ states not only that are we not central to the universe but that no one can be central, because the universe ____

isotropic theory ; is expanding

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