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WorksheetsReview - The Stars
Total questions: 20
Worksheet time: 40mins
When an astronomer rambles on and on about the luminosity of a star she is studying, she is talking about:
what color the star is
the total amount of mass in the star
the star's apparent size (the size seen from Earth)
how much energy the star gives off each second
Using a good pair of binoculars, you observe a section of the sky where there are stars of many different apparent brightnesses. You find one star that appears especially dim. This star looks dim because it is:
very far away
very low luminosity
radiating most of its energy in the infrared region of the spectrum
it could be more than one of the above; there is no way to tell which answer is right by just looking at the star
Which of the following looks the brightest in the sky?
a star with magnitude 10
a star with magnitude 6
a star with magnitude -1
you can't fool me, all of the above look equally bright from Earth
Which color star is likely to be the hottest?
red
blue-violet
yellow
orange
Most of the stars we can see with the unaided eye from Earth are
very close to us (among the closest stars)
more luminous (intrinsically brighter) than the Sun
only visible to our eyes because they actually consist of three or more stars blending their light together
undergoing some sort of explosion which makes their outer layers unusually bright
An H-R Diagram plots the luminosity of stars against their:
mass
diameter
surface temperature
age
Who was the astronomer who is the "H" in H-R diagram?
Hubble
Hertzsprung
Huggins
Hoyle
Ninety percent of all stars (if plotted on an H-R diagram) would fall into a region astronomers call:
the supergiant region
the main sequence
the white dwarf region
the visual region
Astronomers identify the main sequence on the H-R diagram with what activity in the course of a star's life?
fusing hydrogen into helium in their cores
letting go of a huge outer layer
dying
you can't fool me; so many stars are on the main sequence that there is no special stage in a star's life that can be identified with it
Astronomers call a ball of matter that is contracting to become a star
a giant molecular cloud
a planet
a protostar
a main sequence star
A star whose temperature is increasing but whose luminosity is roughly constant moves in what direction on the H-R diagram?
to the right
to the left
upwards
downwards
Astronomers identify the "birth" of a real star (as opposed to the activities of a protostar) with what activity in the star?
when it starts to contract rapidly from a cloud of gas and dust
when it first becomes visible inside its dust cloud
when nuclear fusion reactions begin inside its core
when it glows with infrared radiation
When a star settles down to a stable existence as a main-sequence star, what characteristics determines where on the main sequence in an H-R diagram the star will fall?
its mass
the fraction of its atmosphere that consists of hydrogen
the speed and direction of its rotation
the size of the disk around it
Why do all stars spend most of their lives on the main sequence?
because the neutrinos created inside the Sun do not carry any energy away with them
because during this stage the star contracts from enormous size to a relatively small ball; this takes a long time
because the fuel for energy production in this stage of the star's life is hydrogen; and that is an element every star has lots and lots of
because in this stage, the processes inside the star do not generate any energy; thus the star can continue in this stage indefinitely
Which of the following statements about the main sequence stage in the life of a star is FALSE?
all stars spend the majority of their lives in the main sequence stage
during the main sequence stage, energy to power the star is provided by the fusion of hydrogen
main sequence stars are rare in the Galaxy, so we are lucky to be living around one
different stars spend a different amounts of time (number of years) in the main sequence stage, depending on the characteristics they were born with
When a single star with a mass equal to the Sun dies, it will become a
white dwarf
neutron star
black hole
pulsar
Why are astronomers much more interested in the luminosity of a star than its apparent brightness?
because luminosity can be measured exactly, but apparent brightness can only be roughly estimated
because the luminosity tells us how bright a star really is, while apparent brightness only tells us how bright it happens to look from Earth
because the luminosity also tells us what elements the star is made of, while apparent brightness cannot tell us a star's chemical make-up
you can't fool me, there is no difference between luminosity and apparent brightness; they are merely different terms for the same property of a star
Studies of the spectra of stars have revealed that
the element that makes up the majority of the stars (75% by mass) is
stellarium
hydrogen
helium
carbon
Most of the really bright stars in our sky are NOT among the stars that are very close to us. Why then do they look so bright to us?
we see them in crowded regions of stars, which give us the impression that the stars there are brighter than they really are
all the brightest stars are red, and red color is much easier to see against the black night sky
these stars vary in brightness (flashing brighter and dimmer) and are thus easier to notice
these stars are intrinsically so luminous, that they can easily be seen even across great distances
Where on the H-R Diagram would we find stars that look red when seen through a telescope?
only near the top of the diagram and never near the bottom
only near the left side of the diagram and never near the right
only on the right side of the diagram and never on the left
only near the bottom of the diagram and never near the top
