Astronomy Chapters 18 & 19

Interstellar gas is composed of:90% hydrogen, 9% helium by weight.
What effect do even thin clouds of dust have on light passing through them?It dims and reddens the light of all more distant stars.
Some regions along the plane of the Milky Way appear dark because:stars in that region are hidden by dark dust particles.
The spectra of interstellar gas clouds show that they have the same basic composition as:stars.
Hydrogen is the major gas in the interstellar medium.True.
There is as much mass in the voids between the stars as in the stars themselves.True.
The “Local Bubble” was probably created by a nearby supernova in the distant past.False.
Emission nebulae like M42 occur only near stars that emit large amounts of:ultraviolet radiation.
What is the primary visible color of an emission nebula?Red, due to ionized hydrogen atoms.
Emission nebula appear red because they are associated with cool red giant stars.False.
The compositions of dark clouds can be determined through absorption spectra.True.
A dark cloud can be detected if it happens to block the light emitted by more distant stars.True.
The most common molecule in a molecular cloud is:molecule hydrogen, H2.
Complex molecules in space are found:in dense dust clouds.
Which of the following has NOT yet been observed in space?DNA.
Our Sun, along with most of the stars in our neighborhood, probably formed:billions of years ago.
What is the force that keeps a main sequence star from blowing apart?gravitation.
The birth of stars is a battle between gravity and radiation pressure.True.
The fundamental difference between a protostar and a star is that the latter has nuclear fusion as its energy source and the former does not.True.
Which event marks the birth of a star?Fusion of hydrogen atoms into helium atoms.
A newly formed protostar will radiate primarily at which wavelength?infrared.
What is the force that keeps a main sequence star from collapsing on itself?Radiation pressure.
At the end of the Kelvin-Helmholtz contraction a star is hundreds of times brighter than it will be as a main sequence star.True.
A cloud fragment too small to collapse into a main sequence star becomes a:brown dwarf.
The single most important determinant of the temperature, density, radius, luminosity, and pace of evolution of a protostar is its:mass.
Besides mass the other factor that influences where a star appears on the main sequence is:chemical composition of the cloud.
Atomic bomb tests demonstrated which aspect of star formation?A shock wave surrounding and compressing a molecular cloud.
Why are star clusters almost ideal “laboratories” for stellar studies?Stars in clusters have the same age, similar composition, and are at the same distance away.
Star clusters have been observed within dark nebulae with:infrared observations.
What are the characteristics of globular cluster stars?Old age and hundreds of thousands to millions of member stars.
All globular clusters in our Milky Way are about how old?Around ten billion years old.