1. Proxima
Centauri is about 4.3 light-years (41 trillion kilometers) away.
2. The most basic method of
determining stellar distances is to use stellar parallax, which is the
extremely slight back-and-forth shifting in a nearby star's position due to the
orbital motion of Earth. As distance increases, stellar parallax will decrease.
3. Apparent magnitude is a measure of how bright a
star appears when viewed from Earth. Absolute magni-tude
is the "true," or intrinsic, brightness of a star independent of its
distance from Earth.
4. A star with an absolute magnitude of five is 100
times more luminous than a star with an absolute magnitude of ten. A star of
the first magnitude is about 2.5 times brighter than a star of the second
magnitude.
5. A star's color is an indication of its surface
temperature.
6. Very hot stars appear blue. Medium-temperature
stars appear yellow, like the Sun. Red stars are much cooler.
7. Binary stars are used to determine the mass of a
star.
8. The more massive a main sequence star, the greater
is its intrinsic brightness (luminosity).
9. Because the absolute brightness of a star is
dependent only on its surface temperature and size, if the star's surface
temperature is known, a good estimate of its size can be made.
10. A star spends most
of its time on the main sequence of an H-R diagram.
11. The Sun is about average. Because the magnitudes
of a vast majority of main-sequence stars lie between
–5 and +15, and because the Sun has an absolute
magnitude of about +5, the Sun is often considered an average star. However,
more main-sequence stars are cooler and less massive than the Sun.
12. Interstellar matter is the original material from
which stars are born.
13. Bright nebulae glow because they are close to a
very hot star. Dark nebulae are not close enough to a bright star to glow and
therefore appear as opaque objects silhouetted against a bright background.
14. Hydrogen is the fuel for main-sequence stars.
15. The giant stage results because the zone of
hydrogen fusion continually migrates outward. After the hydrogen in the star's
core is used up, further contraction heats the star's interior. This energy in
turn heats and enormously expands the star's outer envelope. While the envelope
of a red giant expands, the core continues to collapse and become hotter until
it is hot enough to initiate helium fusion.
16. Less massive stars age more slowly because they
consume their fuel at a slower rate than do massive stars.
17. (1) Gravitational
contraction of a gaseous mass into a protostar
(2) Continual contraction
occurs until the internal temperature reaches 10 million K, at which point the
star begins to generate its own energy via nuclear fusion.
(3) Internal heat prevents further
contraction. The star is a stable main-sequence star.
(4) Hydrogen fusion migrates outward from the core.
All the hydrogen in the core is consumed and the core begins to contract, heat
is generated because of gravitational energy, and the star expands to become a
giant. The core continues to collapse and become hotter until it reaches 100
million K and helium fusion begins.
(5) When the hydrogen and helium fuel is exhausted,
the star collapses into an Earth-sized body of great density—a white dwarf. As
the star collapses it may cast off its outer atmosphere and create a planetary
nebula.
(6) The white dwarf becomes cooler and
dimmer as it radiates its remaining thermal energy to space and may become a
black dwarf.
18. A low-mass star never becomes a red giant. It will
remain a main-sequence star until it consumes its fuel, collapses, and becomes
a white dwarf.
19. A medium-mass (Sun-like) star becomes a red giant.
When its hydrogen and helium fuel is exhausted, it collapses and becomes a
white dwarf. During the collapse, a medium-mass star may cast off its outer
atmosphere and produce a planetary nebula.
20. A massive star terminates in a brilliant explosion
called a supernova. The two possible products of a supernova event are a
neutron star or a black hole.
21.
The Milky Way is a large spiral galaxy with at least three distinct spiral arms
and a galactic nucleus. Surrounding the galactic disk is a nearly spherical
halo made of very tenuous gas and numerous globular clusters.
22. The most
obvious difference among the three general types of galaxies is their shape, as
denoted by their names: elliptical, spiral, and irregular. The most important
difference is the age of the stars of which each type is composed. Irregular
galaxies are composed mostly of young stars, whereas elliptical galaxies
contain mostly older stars. Spiral galaxies, like the Milky Way, are composed
of stars of various ages, with the youngest stars located in the arms.
23. Many of the elliptical galaxies
are very small, which makes their detection less likely.
24. When Hubble detected unique stars
in Andromeda Galaxy, he concluded that for these intrinsically bright stars to
appear very dim, they must lie outside the Milky Way.
25. One line of evidence that
supports the big bang is that the red shift in the spectra of galaxies indicates
that they are moving away from one another.
Answers to Earth System Questions
1. During the catastrophic death of stars massive
numbers of atoms of carbon, iron, and other elements are formed. It was from
the debris of stellar deaths that the nebula that became our solar system
evolved. Because the atmosphere, hydrosphere, solid Earth, and biosphere all
contain these atoms, they are all related to the death of a star(s) that
occurred billions of years ago.
2. Intense x-ray and gamma radiation
from a supernova explosion within the immediate vicinity of our solar system
could have a devastating effect on Earth. Perhaps the most serious consequence,
depending on the intensity of the radiation, would be either the complete
annihilation or radical mutation of life. Since the biosphere interacts with
the remaining spheres, the entire Earth system would eventually be altered.
3. Given that stars and planets form
from the collapse of a nebula, and many young stars contain nebular discs of
dust and gas around them, it appears likely that many different types of stars
may have a planet or planets surrounding them. Assuming that only Sun-like
stars have planets, then there are a couple hundred
million candidates in our own galaxy. Whether the planets are suitable for life
depends on their compositions, temperatures, and other factors. However, the
presence of planets and molecules like water or carbon dioxide does not imply
life; these items are only the precursors to life.
4. Although answers are based on
opinion and may vary, it appears that extrasolar
planets similar to Earth are not very likely to exist. To produce such a planet
would require such a unique set of circumstances, occurring in a very set
pattern, that the odds of their happening are extremely small.