a large interstellar gas and dust cloud containing many young stars.
How does the average density of the Sun compare to that of Jupiter?
The Sun has approximately the same average density as Jupiter.
The Hertzsprung-Russell diagram is a statistical plot of which of the following two stellar parameters?
luminosity and surface temperature
An astronomer observing certain regions of the Sun through a spectrograph notices that the spectral lines emitted from these regions are split into two or more components. What can the astronomer conclude about these regions from this observation?
They contain strong magnetic fields.
The relationship between mass and luminosity of stars on the main sequence is that
the greater the stellar mass, the larger the luminosity.
The phrase "hydrostatic equilibrium" in the Sun refers to
the balance of gravity inward and gas pressure outward.
When is electron degeneracy pressure important in a star?
just before the start of helium burning in the core
The spectral type of a star is most directly related to (and determines uniquely) its
What occurrence defines the end of the protostar phase of a star's life and the start of the main-sequence phase?
Nuclear reactions begin in its core
On the Hertzsprung-Russell diagram
in which direction does the position occupied by a star move after hydrogen burning ends in the star's core?,toward the upper right
Sunspots are caused by
differential rotation and its effect on weak magnetic fields.
A white dwarf star is supported from collapse under gravity by
degenerate-electron pressure in the compact interior.
At what distance are stars assumed to be from the Earth when they are represented by their absolute (as opposed to their apparent) magnitude?
The star Acturus is classified as a K2 III
which means that it is a ,cool giant.
Which are the two most abundant elements in the universe?
hydrogen and helium
In a semidetached binary star system
one star fills its Roche lobe, while the other does not.
The temperature at which thermonuclear reactions begin to convert helium into carbon (helium burning) is
100 million K..
What is the characteristic color of an emission nebula?
What process provides the power for the Sun?
fusion of hydrogen into helium
The transfer of mass from the surface of one star onto the surface of another is most often observed in
A coronal hole shows up most prominently in photographs taken at what wavelengths?
All stars on the main sequence
generate energy by hydrogen fusion in their centers.
The effect of interstellar dust on starlight is
to dim and redden distant stars by preferentially scattering their blue light.
The helium flash results from
electron degeneracy or quantum crowding in the core of a low-mass red giant star.
The corona of the Sun has a temperature
of 1 to 2 million K.
A white dwarf is
a low mass star at the end of its life.
What is the last nuclear burning stage in the life of a low-mass star like the Sun?
fusion of helium nuclei to form carbon and oxygen
From the center outward
the order of the layers or parts of the Sun is,radiative zone, convection zone, photosphere, chromosphere, corona.
Protostars are stars
that are slowly contracting and heating up.
The total time the Sun will spend as a main sequence star is
about 10 billion years.
Apparent magnitude is a measure of the
brightness of a star, as seen from the Earth.
Proper motion of a star is defined as its
apparent motion across our sky against the background stars.
The study of stars in clusters has helped astronomers to understand
stellar evolution- the development of stars with time.
If stellar parallax can be measured to a precision of about 0.01 arsec using telescopes on the Earth to observe stars
to what distance does this correspond in space? ,100 pc
There is a mass limit for a star in the white dwarf phase
the Chandresekhar limit, beyond which the star can no longer support its own weight. This mass limit, in terms of solar mass, is,1.4.
How much longer can the Sun continue to generate energy by nuclear reactions in its core?
about 5 billion years
The age of a cluster can be found by
determining the turnoff point on the main sequence of its HR diagram.
What is the most important factor that determines the point in the Hertzsprung-Russell diagram where a protostar reaches the main sequence?
the mass of the protostar
Granulation on the surface of the Sun is caused by
convective currents carrying heat from beneath the surface.
Which of the following four spectral classifications represents the hottest stellar surface temperature?
The spectral sequence of star surface temperature
as determined by relative spectral absorption line strengths, has been given which sequence of letters, in order of decreasing temperature? ,OBAFGKM
The evolution of a star is controlled mostly by its
The neutrino is
an elusive subatomic particle, having very little or no mass and difficult to detect.
The bright stars at the center of an H II region (an emission nebula) are mostly
young O and B stars.
cooler, darker regions on the Sun's surface.
A brown dwarf is
an object intermediate between a planet and a star, with not enough mass to begin nuclear reactions in its core.
The temperature of the Sun's photosphere is
What fraction of the stars in the night sky are main-sequence stars?
almost all of them, about 90%
What is a red giant?
a star burning hydrogen into helium in a shell around the core
What name is given to the visible "surface" of the Sun?