Can You Answer the Following
1. Clouds of interstellar gas and dust which can be seen throughout
a galaxy are broadly
termed _______________. There are four basic
varieties: reflection, diffuse or emission,
dark, and planetary.
2. The densities of gaseous nebulae are very low. Even the brightest
contain only about 100 /
10,000 / 1,000,000 (circle one) atoms or ions
per cubic centimeter. Under standard
conditions, air has a particle density of 2.7
x 1019 molecules per cubic centimeter.
3. _______________ nebulae are normally found in OB-associations where
from nearby luminous stars (T > 25,000 K)
causes the gases in the cloud to emit light in their
own colors. The Orion nebula, located in the
center of the sword of Orion, the hunter is
probably the best example of this type of nebulosity.
These types of nebulae are associated
with stellar BIRTH/MATURITY/DEATH (Circle One).
They almost always have cold
regions of _______________ embedded in the hot
(approx. 10,000 K) gas implying a lack
of thermodynamic equilibrium. These types of
nebulosities produce an
EMISSION/CONTINUOUS/ABSORPTION (circle one)
4. ______________ nebulae can be seen because of the light which they
scatter from nearby
stars. These clouds are composed of very small
grains of _______________ which are
nearly the same size as the light being emitted
by the stars which are causing them to shine.
This light is therefore SCATTERED/REFLECTED
(circle one). The Pleiades, a star cluster
located on the "shoulder" of Taurus,
the bull contains one of the best examples of this type of
5. _______________ nebulae are formed when low mass stars, near the
end of their lives,
eject a shell of gaseous matter which is made
to glow from energy escaping the degenerate,
hot core of a ____________________ star. The
ring nebula in Lyra highlights such an
object. These types of nebulosities produce
EMISSION/CONTINUOUS/ABSORPTION (circle one)
6. _______________ nebulae reveal themselves when large interstellar
clouds of dust absorb
the radiation from stars which lie behind them.
These clouds which also contain hydrogen
and helium gas, are associated with stellar
BIRTH/MATURITY/DEATH (circle one). The
Horsehead nebula, near the southern end of the
belt of Orion is a prime example of this type
7. In interstellar nebulae there ore often compact clouds of dust
having moderately high
densities. These can shield the local environment
from high energy radiation (particularly the
short ultraviolet) allowing for the formation
of molecules which can be detected through their
radio emissions. The detection of interstellar
molecules by radio astronomers serves as a
tracer for the location of regions where stellar
_______________ may be occurring.
8. Cold neutral hydrogen atoms neither absorb nor emit light at optical
wavelengths, but they
do emit radiation at a wavelength of 21 cm in
the _______________ region of the
electromagnetic spectrum. This results when
the ground state electron of a hydrogen atom
spontaneously changes its spin from the same
direction as the proton to the opposite
direction of the proton.
9. Clouds of interstellar neutral hydrogen are referred to as _______________
clouds of ionized hydrogen, found in diffuse
and planetary nebulae are called
10. Absorption by interstellar dust is more prevalent NEAR THE PLANE
GALAXY/NEAR HIGH GALACTIC LATITUDES (circle
one). All stars at substantial
distances from us appear BRIGHTER/FAINTER (circle
one) and ________________
(color) due to the scattering effects of dust
in the galaxy and throughout intergalactic space.
This tells astronomers something about the average
size of the dust particles, which can be
no more than about 0.1 micron or 10-5 cm in
diameter. Typically this dust is composed of
________________, ________________, ________________,
11. The vast majority (about 99 percent) of interstellar matter is
found in the form of
DUST/GAS (circle one) which DOES/DOES NOT (circle
one) absorb starlight.
THE MILKY WAY GALAXY
12. The sun is located in a huge stellar system known as the ____________________
The word galaxy is derived from "galas,"
the Greek word for _______________.
13. From the top down, our galaxy appears similar to a _______________
_______________ arms emanating from a central
_______________ where the density of
stars is the greatest.
14. Viewing our galaxy from its equatorial plane, it appears as a
structure with a central _______________. Mapping
the galaxy has proven to be a very
complex matter. We cannot observe the center
of the galaxy, because there is an enormous
amount of interstellar matter between us and
the galactic nucleus. This fog results from the
GAS/DUST (circle one) component of interstellar
matter found within the Milky Way.
15. Our galaxy's diameter is approximately ______________ light years.
While most of the
matter appears to reside near the galactic plane,
a huge halo of _______________ clusters,
spherically symmetrical compact groupings of
stars, each containing from about 10,000 to
one million members occupies the regions above
and below the plane of the Milky Way.
16. The galactic equator runs through the middle of the band of light
we refer to as the
___________________. It is inclined 62 degrees
to the plane of the celestial equator and
extends 360 degrees around the sky. This implies
that we are not at the _______________
of this system. Current estimates place the
solar system at a distance of approximately
_______________ light years from the galactic
17. There appears to be two different populations of stars in the
Milky Way. These can be
described as _______________ rich or poor stars.
These two broad categories of stars
occupy specific regions in spiral galaxies like
our Milky Way. Before a star is considered
metal rich, at least _______________ percent
of its mass must be contained in elements
heavier than hydrogen and helium.
18. Population _______________ stars can be found in the galactic
center, as well as the
halo, which defines the realm of the globular
clusters. Population _______________ stars
are found in the spiral arms of the galaxy.
19. Identify the two populations of stars found in the Milky Way with
Interstellar Gas and Dust
20. The mass of the Milky Way is now believed to be about _______________
This is higher than earlier estimates, because
it is now realized that the galactic
_______________ is much more massive than previously
assumed. Not all of the mass in
the galaxy appears to be observable in stars
and interstellar matter. In the center of the
galaxy, where densities are HIGHEST/LOWEST (circle
one), a super massive
____________________ may reside.
21. As the galaxy rotates, stars in the galactic plane travel in _______________
around the nucleus. The orbital speed of the
sun is about 150 miles/sec (250 km/sec) and it
takes about 200 million years to complete one
GALAXIES IN GENERAL
22. The basic way that matter congregates in the universe is in the
form of ____________.
23. The Milky Way Galaxy is one of several THOUSANDS/MILLIONS/BILLIONS
one) of island universes which are known to
inhabit the universe in which we live. Only three
other systems are easily visible to the unaided
eye. The largest and most distant of these is
the great spiral galaxy called _________________,
which lies at a distance of 2.1 million
light years from the sun. It is slightly more
massive than the Milky Way. The other two are
the Large and the Small _________________________,
satellite systems of our own
Milky Way which can only be observed from the
24. Galaxies were classified by the astronomer Edwin _______________
in the 1920's
according to their appearance and structure.
These fall into three broad categories: spirals,
ellipticals, and irregulars.
25. _______________ galaxies tend to be large to very large as galaxies
go and have
population II stars in their nuclei and halos,
plus population I stars with plenty of interstellar
gas and dust in their arms.
26. _______________ range from very small, for galaxies, to extremely
large. They seem to
consist of population II stars only, and they
have little gas or dust.
27. _______________ tend to be smallish, for galaxies, and have many
population I stars
along with substantial quantities of gas and
28. The Milky Way and Andromeda galaxies are the two largest members
of a cluster of about
_______________ (number) galaxies called the
____________________. At least one
other spiral (Messier 33) and several irregular
and dwarf elliptical galaxies coexist in this
assemblage. Most galaxies are FOUND/NOT FOUND
(circle one) in clusters.
29. The nearest giant cluster of galaxies is the _______________ cluster
several DOZENS/THOUSANDS (circle one) of galaxies.
The largest galaxy of this cluster
is Messier 87, a giant elliptical, which is
among one of the most massive galaxies known.
30. Most typical galaxies produce ABSORPTION/EMISSION (circle one)
arise as a composite signature of the different
types of stars which are contained in them. A
group of peculiar galaxies, known as _______________
galaxies, however, have emission
lines and very bright nuclei.
31. There also exists another type of peculiar galaxy which emits
far more radio noise than
normal. These galaxies are known as _______________
galaxies. Some of the radio
radiation arises from the cores of these structures,
but most of these galaxies also display
lobes filled with high-energy electrons which
are located outside the optical limits of the
32. The two types of peculiar galaxies mentioned in the last several
problems are also referred
to as _______________ galaxies. They apparently
have violent processes taking place in
their cores which may be the result of rapidly
rotating disks of matter plunging into large,
super massive ____________________.
33. Even more peculiar than the active galaxies are _______________,
which are only seen at
very great distances. They appear starlike and
are often variable in light. These objects
generate huge amounts of energy across the entire
electromagnetic spectrum from a very
small volume of space. They are probably the
cores of very young and extremely active
34. All matter-energy everywhere is a good definition for the __________________.
35. The study of the large-scale structure of the universe is known
It is by far the most speculative branch of
present-day astronomical research.
36. In 1823 Heinrich _________________ published a paper on why the
sky is dark at night.
If the universe were infinite in extent, there
would be an infinite number of stars in the sky and
every available space in the heavens would be
occupied by a luminary. The night sky should
therefore have the same brightness as the surface
brightness of a typical star. Why then is the
nighttime sky dark? Explain the riddle of ________________
Paradox using the following
clues as a guide.
a. Is the universe infinite?
b. The expanding universe:
c. The red shift:
37. In 1916 Albert Einstein demonstrated that the universe could not
be static; it must either
expand or contract. During the next two decades,
Georges Lemaitre and George Gamow
proposed that the entire visible universe had
been formed from a single primordial event,
known as the ___________________.
38. In 1924 Edwin _______________ was able to conclusively prove that
the so-called spiral
and elliptical nebulae were in fact galactic
systems in their own right. In 1929 he determined
that all of the more distant galaxies were _______________
from us at rates which were
proportional to their distances. Remember, that
the determination of the distances to galaxies
must be obtained without knowing their red shifts
or there is no way one can independently
correlate expansion rates (red shifts) with
39. The Hubble constant, H0, is a determination of the rate at which
the universe is
_______________. It is measured in kilometers/second--
megaparsec. The best
determination of H0 at present is _______________
km/sec-- Mpc. One megaparsec equal
one million parsecs or 3.26 million light years.
40. Current estimates of the Hubble constant range from 45-75 km/sec--
Mpc. It is an
extremely important number to clarify, for it
gives astronomers the ability to determine the
_______________ of the universe. The current
value of H0 implies a 20 billion year old
universe, or the maximum time since the big
bang. A lower constant suggests an (a)
OLDER/YOUNGER (circle one) universe because
if would take objects longer to reach
their observed distances. If H0 = 30 km/sec--
Mpc, then the universe would be
approximately 30 billion years of age. A higher
constant implies just the opposite. In fact if
H0 = 75 km/sec-- Mpc, then the universe can
only be about 13 billion years of age. The
reciprocal of the Hubble constant is known as
the Hubble time (T0 = 1/H0).
41. The oldest stars in the Milky Way galaxy are about _______________
billion years of age.
Since these luminaries could only have been
formed well after the big bang, it is
EASY/DIFFICULT (circle one) to reconcile their
ages with a Hubble constant as large as 75
42. When we look out into space we are also looking back into ______________.
out we see, the EARLIER/LATER (circle one) into
the history of the universe we peer.
43. Quasars have provided astronomers with evidence for an evolutionary
universe, that is, a
universe which changes with time. How?_______________________________________
The 3 K microwave background radiation represents
the first visible artifact of the big bang
itself, where the universe had thinned and cooled
to the point that energy could escape. It also
gives credence to an evolutionary universe since
the big bang was a once and done event which
happened at the creation of space and time.
44. One variant of the big bang hypothesis is a universe that will
have a sufficiently high enough
mean _______________ so that gravity will halt
its expansion and force it to collapse upon
itself to perhaps rekindle yet another big bang
event sometime in the future. This type of
accordion universe is called an _______________
45. If the mean density of the universe is less than the closure density,
the universe will
____________________. Such a universe is termed
an _______________ universe. Present
observations indicate that the universe is probably
46. Over the years there have been other cosmological models which
do not invoke a primordial
event. One of these hypotheses, first proposed
in 1948 by Gold, Hoyle, and Bondi suggested a
universe that was infinite in space and time,
expanding, and homogeneous. Hydrogen was being
created in the voids formed by the expanding
galaxies. This hypothesis, no longer considered
valid, is called the ____________________ theory.