Chapter Four, Deep Space
CHECKPOINTS
Below are the answers to the items listed at the end of the lesson in the student textbook edition
of Exploring Space: The High Frontier. These end-of-lesson items are not assigned in the lesson
plans. The answers are provided here in case you want to assign any of them in your classes, for
homework, or if your students ask you about them. They are in the same order as listed in the
student textbook.
1. The Sun is one of how many stars that make up the Milky Way Galaxy? The Sun is one of
about 200 billion stars that make up the Milky Way Galaxy. (p. 149)
2. How are the stars of the galaxy arranged? Most of the galaxy’s stars are arranged in a wheelshaped disk that circles around a bulging center. (p. 149)
3. Why were twentieth-century scientists skeptical of claims that the Sun was near the center of
the galaxy? Scientists were conscious enough of Ptolemy’s miscalculation of the Solar
System that they were naturally skeptical of a claim that the Sun was at the center. (p. 151)
4. What do the Magellanic clouds and the Andromeda galaxy have in common? Both the
Magellanic clouds and the Andromeda galaxy are visible in the sky but are not part of the
Milky Way Galaxy. (p. 151)
5. What are most of the stars in the disk of the galaxy like? Why does the disk have a bluish
cast? Most of the stars in the galaxy are young. The bluish cast seems to have something to
do with the formation of new stars. (p. 152)
6. Why does the nuclear bulge of the galaxy have a reddish cast? The bulge has a reddish cast
because it contains so many red giant and supergiant stars. (p. 152)
7. What did Harlow Shapley find when he counted globular clusters? Globular clusters
provided astronomer Harlow Shapley with the data he needed to place the Sun correctly
some distance from the center of the Milky Way Galaxy. (p. 152)
8. What do scientists think the galactic corona includes? Scientists think the galactic corona
may consist of small black holes, cool dwarf stars, larges numbers of neutrinos, and other
exotic particles. (p. 153)
9. Why has infrared technology, measuring electromagnetic waves below the range of visible
light, been such a boon to astronomers? It modifies the imbalance between a bright star and
a dim planet. In the infrared, the brightness of a planet peaks, while that of a star declines.
(p. 154)
10. What is gravitational microlensing? Microlensing is the term for temporary brightening of
the light from a distant star orbited by an object such as a planet. (p. 157)
Lesson One, The Milky Way Galaxy
251
Chapter Four, Deep Space
11. What is the core-accretion model of planetary formation? The core-accretion model assumes
that planets start out as small chunks of rock, dust, and debris. After a series of collisions
among planetesimals and the accretion of dust and gas, they eventually turn into a planet.
(p. 157)
12. Scientists can describe any black hole using which three numbers? Science can describe any
black hole using only three numbers: one for its mass, one for its electric charge, and one for
it angular momentum. (p. 158)
13. Why would a black hole be expected to spin rapidly? What effect would it have on nearby
space-time? As an object shrinks, its rotation rate speeds up. Therefore a rapidly spinning
black hole would drag nearby space-time around with it. (p. 158)
14. Why would astronomers use indirect observation for their work on black holes rather than
direct observation? There’s no hope of directly seeing something from which no light
escapes. That has turned astronomers’ thoughts to indirect observation. (p. 159)
15. How do scientists observe the galactic nucleus? To observe the galactic nucleus, scientists
use wavelengths in the infrared/radio part of the spectrum or in X-rays and gamma rays.
(p. 160)
16. What is currently the best explanation of the energy source of the Milky Way and other spiral
galaxies? The massive-black-hole hypothesis seems to be the best explanation for the energy
source in the Milky Way Galaxy and other similar galaxies. (p. 160)
Applying Your Learning
17. Astronomers discovered interstellar dust in 1930. How did failure to understand the
phenomenon earlier lead to incorrect estimates of the Sun’s position on the disk of the Milky
Way Galaxy? Scientists couldn’t see the edge of the galaxy and they didn’t realize they
couldn’t. They saw lots of stars, but they didn’t know that interstellar dust was keeping them
from seeing more distant ones. (p. 151)
Lesson One, The Milky Way Galaxy
252
Chapter Four, Deep Space
Activity 1: Review Relay
M
I
L
K
Y
What is the outermost part of a spiral galaxy, nearly spherical and
lying beyond the spiral?
What is a rotating neutron star that emits beams of radio waves that
are observed as pulses of radio waves with a regular period?
What is the large, flat part of a spiral galaxy, rotating around its
center?
What is a rotating disk of gas orbiting a star, formed by material
falling toward the star?
What is an uncharged or electrically neutral particle believed to have
little or no mass?
W
A
Y
What are planets that orbit stars outside the Solar System called?
G
What is the branch of astronomy dealing with measurement of the
positions and motions of celestial bodies?
Who is the radius of a sphere around a black hole from within which
no light can escape named after?
What lies beyond the galaxy’s halo?
A
L
A
X
Y
What is a spiral galaxy’s central region?
What is a star that grows brighter than usual for a time and then
returns to its original state.
What is the speed at which an object must travel to “escape” a star’s
gravity?
What is a star-like object that gives off light but lacks sufficient
mass for nuclear reactions in its core?
What is the spiral galaxy that is about 2.9 million light-years from
the Milky Way?
I
S
What is an object whose escape velocity exceeds the speed of light?
H
O
What is a pair of stars that revolve around each other?
M
E
What is the distance that light travels in a vacuum in one year (about
5.9 trillion miles or 9.5 trillion km)?
What is a spherical group of up to hundreds of thousands of stars,
found primarily in a galaxy’s halo?
What is an astronomical unit that is equal to 3.26 light-years?
What is the temporary brightening of the light from a distant star
orbited by an object such as a planet?
Lesson One, The Milky Way Galaxy
253
Chapter Four, Deep Space
Activity 1: Review Relay Answer Key
What is the outermost part of a spiral galaxy, nearly spherical and
lying beyond the spiral?
What is a rotating neutron star that emits beams of radio waves that
are observed as pulses of radio waves with a regular period?
What is the large, flat part of a spiral galaxy, rotating around its
center?
What is a rotating disk of gas orbiting a star, formed by material
falling toward the star?
What is an uncharged or electrically neutral particle believed to have
little or no mass?
Halo (p. 152)
W
What are planets that orbit stars outside the Solar System called?
A
What is a spiral galaxy’s central region?
Y
What is a star that grows brighter than usual for a time and then
returns to its original state.
Exoplanets
(p. 148)
Nuclear Bulge
(p. 152)
Nova (p. 159)
G
What is the branch of astronomy dealing with measurement of the
positions and motions of celestial bodies?
Who is the radius of a sphere around a black hole from within which
no light can escape named after?
What lies beyond the galaxy’s halo?
M
I
L
K
Y
A
L
A
X
Y
What is the speed at which an object must travel to “escape” a star’s
gravity?
What is a star-like object that gives off light but lacks sufficient
mass for nuclear reactions in its core?
What is the spiral galaxy that is about 2.9 million light-years from
the Milky Way?
Pulsar (p. 155)
Galaxy Disk
(p. 152)
Accretion Disk
(p. 157)
Neutrino (p. 153)
Astrometry
(p. 155)
Schwarzschild
(p. 158)
Galactic Corona
(p. 153)
Escape Velocity
(p. 157)
Brown Dwarf
(p. 154)
Andromeda
(p. 151)
I
What is an object whose escape velocity exceeds the speed of light?
S
What is the distance that light travels in a vacuum in one year (about
5.9 trillion miles or 9.5 trillion km)?
H
What is a pair of stars that revolve around each other?
O
What is a spherical group of up to hundreds of thousands of stars,
found primarily in a galaxy’s halo?
What is an astronomical unit that is equal to 3.26 light-years?
Binary Star
System (p. 155)
Globular Cluster
(p. 152)
Parsecs (p. 150)
What is the temporary brightening of the light from a distant star
orbited by an object such as a planet?
Microlensing
(p. 157)
M
E
Lesson One, The Milky Way Galaxy
254
Black Hole
(p. 157)
Light-year
(p. 149)
Chapter Four, Deep Space
Activity 2: Discovering Exoplanets
Name ____________________________________Date___________Class_______________
Directions: Use your text to answer the following questions about the discovery of exoplanets.
1. What is NASA doing to find new worlds?
2. What is the name of the sensitive instrument that NASA is proposing to send to space to
provide scientists with images of nearby planetary systems?
3. Your text outlines seven different methods for finding exoplanets that scientists have
developed. Please identify each one and provide a brief description of each.
a.
b.
c.
d.
e.
f.
g.
4.
What is the significance of searching for exoplanets? Do you think scientists will ever find
an exoplanet like Earth with life on it?
Lesson One, The Milky Way Galaxy
255
Chapter Four, Deep Space
Activity 2: Discovering Exoplanets Answer Key
1. What is NASA doing to find new worlds? NASA is embarking on a series of missions to
find these new worlds. To this end, the agency will send out some of the most sensitive
instruments ever built, able to reach beyond the Solar System’s limits.
2. What is the name of the sensitive instrument that NASA is proposing to send to space to
provide scientists with images of nearby planetary systems? The Terrestrial Planet Finder
3. Your text outlines seven different methods for finding exoplanets that scientists have
developed. Please identify each one and provide a brief description of each.
(1) Direct observation/infrared companion: The first direct image of an exoplanet was
obtained in April 2004. The planet is five times as massive as Jupiter and orbits a brown
dwarf – a star-like object that gives off light but lacks sufficient mass for nuclear
reactions in its core. Infrared technology made it possible to find.
(2) Dust disks: Astronomers have found disks of dust and gas the size of the Solar System
around several stars. Such dust generally either gets blown out of a star system or fuses
to the star. That this dust is there all the time suggests that collisions among
planetesimals orbiting the star probably keep replacing it. Gaps in the dust imply the
presence of a planet orbiting the star.
(3) Pulsar companions: A pulsar is a rotating neutron star that emits beams of radio waves
that, like a lighthouse beacon, are observed as pulses of radio waves with a regular
period. In 1992 astronomers reported finding variations in the rate of signals from the
pulsar PSR 1257 + 12. Such variations can signal the presence of one or more companion
objects, such as a planet.
(4) Binary systems and visual wobble: A binary star system is a pair of stars that revolve
around each other. Sometimes only one of a pair is visible to astronomers. But they can
deduce the existence of the other by looking for a bit of wiggle or wobble in the body
they can see. It’s not easy to detect the wobble of a star by carefully measuring its
position in the sky relative to other stars. Astrometry is the branch of astronomy dealing
with measurement of the positions and motions of celestial objects.
(5) Binary systems and Doppler wobble: Another way to detect an exoplanet is to measure
the Doppler shift of a star’s spectrum. That is, scientists measure changes in the light a
star gives off as the star alternately wobbles toward and away from Earth.
(6) Stellar occultation: When a star seems to dim, that can be a sign of occultation – of a
planet passing in front of the star and blocking its light.
(7) Gravitational microlensing: Microlensing is the term for a temporary brightening of
the light from a distant start orbited by an object such as a planet.
4. What is the significance of searching for exoplanets? Do you think scientists will ever find
an exoplanet like Earth with life on it? Student answers will vary.
Lesson One, The Milky Way Galaxy
256
Chapter Four, Deep Space
Activity 3: When Scientists and Astronomers Are Wrong
Name ____________________________________Date___________Class_______________
In previous lessons in this class, you learned that scientists were wrong when they once assumed
that the planets and Sun revolved around the Earth—rather than the heliocentric model we now
know to be true. Today, in this lesson, you have learned that scientists were again mistaken
when they thought that the Sun was at least fairly near the galaxy’s center (pp. 150-151).
Directions: In your assigned groups, brainstorm what areas of astronomy you think scientists
today may be mistaken about. Come up with as many ideas you can in five minutes. Then be
prepared to share your list with the class.
Brainstorming Ideas
Lesson One, The Milky Way Galaxy
257
Chapter Four, Deep Space
Technology Enrichment: No Escape: The Truth About Black Holes
Name ____________________________________Date___________Class_______________
Go to this website:
http://amazing-space.stsci.edu/resources/explorations/blackholes/lesson/index.html


First, click on “How to Use This Site” to find out about navigating through this website.
Then, explore the rest of the site. Make sure you read
o Is a Black Hole Really a Hole?
o No Escape
o See A Black Hole in Action
o What do You Know About Black Holes?
o Pathway to Discovery
o What Types of Black Holes Are There?
o Hubble Hunts Black Holes
Answer the following questions as you explore the website.
1. What is the relationship between escape velocity, black holes and the speed of light?
2. What are the three different types of black holes?
1.
2.
3.
3. How large can the volume of a black hole get?
4. Will the Sun ever become a black hole?
5. Why would a probe NOT be able to send back data from a black hole?
6. Who first predicted the existence of black holes and when was that?
Lesson One, The Milky Way Galaxy
258
Chapter Four, Deep Space
7. Fill in the table about the Hubble instruments featured in this web site.
Full Name
What does it do?
STIS
WFPC2
FOC
Lesson One, The Milky Way Galaxy
259
Weight
(in lbs)
Dimensions
(in feet)
Chapter Four, Deep Space
Technology Enrichment: No Escape: The Truth About Black Holes
Answer Key
1. What is the relationship between escape velocity, black hole and the speed of light? A black
hole is an object - typically a collapsed star - whose gravity is so strong that its escape
velocity exceeds the speed of light. Since nothing is known to exceed the speed of light,
nothing can escape from a black hole.
2. What are the three different types of black holes?
1. Stellar
2. Supermassive
3. Miniature
3. How large can the volume of a black hole get? The volume of a black hole approaches zero.
4. Will the Sun ever become a black hole? Stars the size of the Sun typically do not become
black holes because they lack sufficient mass.
5. Why would a probe NOT be able to send back data from a black hole? If a probe were to
reach a black hole, it would be unable to send back data, because like light, radio waves which "carry" the data - cannot escape from a black hole.
6. Who first predicted the existence of black holes and when was that? Simon Pierre LaPlace in
1796
7. Fill in the table about the Hubble instruments featured in this web site.
Full Name
What does it do?
Weight
(in lbs)
STIS
Space Telescope
STIS acts like a prism to separate 700
Imaging
light from the cosmos into its
Spectrograph
component colors. This provides
a "fingerprint" of the object being
observed, which tells us about its
temperature, chemical
composition, density, and motion.
WFPC2 Wide Field Planetary It is used to observe and take
619
Camera 2
pictures of just about everything,
recording razor-sharp images of
faraway objects in relatively
broad views.
FOC
Faint Object Camera It serves as Hubble's "magnifying 700
glass" — recording the most
detailed images over a small field
of view.
Lesson One, The Milky Way Galaxy
260
Dimensions
(in feet)
7.1 x 2.9 x
2.9
3.3 x 5 x 1.7
3x3x7