Physics 202 HW questions Ch. 17-23
How far away would a star with a parallax of 0.2 arcsec be from us?
5 parsecs
A star moving toward the Sun will show:
A shift in the spectral lines toward the blue end (as compared to the laboratory positions of these lines)
In an H-R diagram, where can you see the spectral type of a star (whether it is an O type star or a G type star, for example)?
Along the bottom (the horizontal axis)
Why are astronomers much more interested in the luminosity of a star than its apparent brightness?
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
Which color star is likely to be the hottest?
Blue-violet
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
The most stable (tightly bound) atomic nucleus in the universe is:
Iron
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:
It could be any of these; there is no way to tell which answer is right by just looking at the star The items include: Very far away Very low luminosity Partly obscured by a cloud Radiating most of its energy in the infrared region of the spectrum
Measurements show a certain star has a very high luminosity (100,000 x the Sun's) while its temperature is quite cool (3500oK). How can this be?
It must be quite large in size
Which types of stars will spend the longest time (the greatest number of years) on the main sequence?
K
The most common kinds of stars in the Galaxy have
Low luminosity compared to the Sun
Two stars have the same luminosity, but star B is three times farther away from us than star A. Compared to star A, star B will look
Nine times fainter.
Why was the Kepler mission not able to find planets smaller than Mars, even though it was in space (and had no Earth atmosphere to deal with)?
Such planets make dips in the light of the star that are too small for Kepler to detect
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?
These stars are intrinsically so luminous that they can easily be seen even across great distances
A type of star cluster that contains mostly very old stars is
a globular star cluster
The Orion Nebula is
a large cloud of gas and dust illuminated by the light of newly formed stars within it
Elements heavier than iron can be created during:
a supernova explosion
The event in the life of a star that begins its expansion into a giant is
almost all the hydrogen in its core that was hot enough for fusion has been turned into helium
Planets in the habitable zone of their stars:
are at a temperature where water can exist as a liquid
Why did it take astronomers until 1838 to measure the parallax of the stars?
because the stars are so far away that their annual shift of position in the sky is too small to see without a good telescope
Why can a star with a mass like our Sun not fuse (produce) further elements beyond carbon and oxygen?
because they just cannot get hot enough for the fusion of heavier nuclei
Really massive stars differ from stars with masses like the Sun in that they
can fuse elements beyond carbon and oxygen in their hot central regions
Astronomers have noticed that the visible filaments in the Crab Nebula are moving toward us at great speed. How can they know about motions like this?
from the Doppler shift in the line radiation from the nebula
If stars with masses like our Sun's cannot make elements heavier than oxygen, where are heavier elements like silicon produced in the universe?
heavier elements are made in the cores of significantly more massive stars than the Sun, which can get hotter in the middle
A star with a mass like the Sun which will soon die is observed to be surrounded by a large amount of dust and gas -- all material it has expelled in the late stages of its life. If astronomers want to observe the radiation from such a giant star surrounded by its own debris, which bands of the spectrum would be the best to use to observe it?
infrared
The closest star to the Sun, Proxima Centauri, was recently found to have a planet in its habitable zone. Proxima Centauri is a main sequence star with spectral type M. How would its habitable zone differ from the habitable zone of our Sun?
it would be significantly closer to Proxima Centauri than ours is to the Sun
Astronomers must often know the distance to a star before they can fully understand its characteristics. Which of the following properties of a star typically requires a knowledge of distance before it can be determined?
its luminosity
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
What technique did astronomers use to make the first confirmed discovery of a planet around another star like the Sun?
measure the Doppler shift of the lines in the star's spectrum and look for periodic changes in this shift due to the pull of the planet as it orbits the star
How are globular clusters distributed in our Milky Way Galaxy?
mostly in a large spherical halo (or cloud) surrounding the flat disk of the Galaxy
The big surprise about the first planet discovered around another regular star was that it
orbited so close to its star it took only 4 days to go around
An astronomer is interested in a galaxy called M31, the nearest galaxy that resembles our Milky Way. It is about 2 million light-years away. Which technique would be able to give us a distance to this galaxy?
period-luminosity relation for Cepheid variables
A white dwarf, compared to a main sequence star with the same mass, would always be:
smaller in diameter
Astronomers observe a young cluster of stars, where stars with three times the mass of the Sun are still on the main sequence of the H-R diagram. Yet the cluster contains two white dwarfs, each with a mass less than 1.4 times the mass of the Sun. If we can show that the white dwarfs are definitely part of the cluster, how can their presence so soon in the life of the cluster be explained?
stars lose a lot of mass on their way to becoming white dwarfs; and so the white dwarfs could have started out as quite massive stars
How do fragile structures like acetaldehyde (CH3CHO) molecules survive in the harsh environment of interstellar space? Why are they not destroyed by high-energy radiation from stars?
such molecules are found only in dense clouds that have a lot of dust; the dust keeps the radiation from hot stars from reaching the molecules
The telescope that allowed astronomers to discover most of the planets found with the transit method was called
the Kepler mission
When a star first begins the long path toward becoming a red giant, a layer of hydrogen around the core begins to undergo fusion. If this layer was too cold to do fusion throughout the main sequence stage, why is it suddenly warm enough?
the core is collapsing under its own weight and heating up from the compression; this heats the next layer up
If observations of supernovae in other galaxies show that such an explosion happens in a spiral galaxy like the Milky Way on average every 25 to 100 years, why have astronomers on Earth not seen a supernova explosion in our Galaxy since 1604?
the disk of our Galaxy contains a great deal of dust, which tends to block the light of supernova explosions from more distant parts of our Galaxy
What observations about disks of dusty material around young stars suggest that planets may be forming in such disks?
the disks show lanes that are empty of dust within them
If we look back to the first generation of stars made when the Galaxy was first forming, how do they differ from stars being formed today?
the first generation stars contain little or no elements heavier than helium
You are observing a binary star system and obtain a series of spectra of the light from the two stars. In this spectrum, most of the absorption lines shift back and forth as expected from the Doppler Effect. A few lines, however, do not shift at all, but remain at the same wavelength. How can we explain the behavior of the non-shifting lines?
the lines come from interstellar matter between us and the star, not from the stars themselves
Among interstellar clouds, the hotter the cloud, the
the lower the density of particles in it
A neutron star is as dense as
the nucleus of an atom
On an H-R diagram of a cluster of stars, which characteristic of the diagram do astronomers use as a good indicator of the cluster's age?
the point on the main sequence where stars begin to "turn off" -- to move toward the red giant region
When a star undergoes a nova explosion, it may return to its "quiet state" and later become a nova again. What would allow a nova explosion to happen to a star more than once?
the star that goes nova has a companion star near it, which dumps material onto the first star and continues to do so even after the first nova explosion
The dust in the dust clouds in interstellar space consists of
tiny solid grains
A star whose temperature is increasing but whose luminosity is roughly constant moves in what direction on the H-R diagram?
to the left
Some of the interstellar gas in our Galaxy has been heated to millions of degrees, a temperature that surprised astronomers when it was first discovered. How do we now think that gas between stars gets that hot?
very powerful shock waves from exploding stars heat the gas they come into contact with
When a single star with a mass equal to the Sun dies, it will become a
white dwarf
What is the baseline that earth-bound astronomers use to measure the parallax (the distance) of the nearest stars?
½ the diameter of the Earth's orbit around the Sun
