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 ____
on December 21, known as the ____, the sun is at its ____ point on the celestial sphere.
winter solstice / southernmost
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
accurate records of comets and "guest" stars were kept over many centuries by ____ astrologers.
the astronomical knowledge of ancient Greece was kept alive and augmented by ____ astronomers
the apparent " backwards" ( westward motion ) of the planets Mars, Jupiter, or Saturn in the sky relative to the stars is known as ____ motion
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.
Kepler discovered that the shape of an orbit is and ____ not a ____ as it had previously been believed
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.
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 ____
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.
an absorption spectrum is produced when a ____ gas lies in front of a source of continuous radiation.
the experiment that demonstrated as the ____ caused Einstein to realize that light does not always behave like a wave.
when an electron moves to a higher energy level in an atom it ____ a photon of a specific energy.
when an electron moves to a lower energy level in an atom it ____a photon of a specific energy.
the "specific energy" of the photon is exactly equal to the energy ____ between the energy levels involved.
changes in a particular molecular vibration states produce spectral features in the ____ part of the electromagnetic spectrum
changes in the molecular rotational states produce spectral features in the ____ part of the electromagnetic spectrum
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.
CCDs produce images in ____ form that can be easily transmitted , stored and later processed by computers.
Active optics and adaptive optics are both being used to improve the ____ of ground based optical telescopes.
an ____ is two or more telescopes used in tandem to observe the same object, in order to improve angular resolution.
____ , ____ , and ____ astronomy can be done only from above earth;s atmosphere
x - ray, gamma, and ultraviolet
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.
when a charged particle moves, information about this motion is transmitted through space by means of its changing ____ and____ fields.
positions ; electric
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 ____
because the sun emits its peak amount of radiation at about 480 nm its temperature must be about ____ K.
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 ?
if an astronomical object is observed to emit x -rays , it is reasonable to assume that its temperature is very ____
when an observer and / or object emitting radiation move toward each other, the observer sees the radiation shifted to ____ wavelengths
the outer planets jupiter, saturn, uranus and neptune are known a s the ____ planets
asteroids and meteoroids have a ____ composition, in contrast with comets, which have an ____ composition.
rocky ; icy
The U.S. spacecraft ____ is the only probe to have visited each of the giant outer planets.
voyager 2 or new horizon
pencil - beam surveys suggest that the largest structures in space are no larger than ____ Mpc in size.
a ____ value for hubble's constant yields an age for the universe incompatible with the oldest globular clusters
by observing distant galaxies, astronomers have determined that the universe was expanding ____ long ago than it is today
comparing the mass density of radiation and matter , we find that, at the present time, ____ dominates
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
elements heavier than helium were not formed primordially because, as time passed, the density and temperature of the universe____
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 ____
the cosmic microwave background radiation lat interacted with matter when the universe was about____ times its present size
if the theory of inflation is correct, then dark matter must make up about ____ percent of all matter in the universe.
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.
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