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Name _________________________________ Date ________________

Section _________________________________ Score ________________
Partner _________________________________ I.I’s ________________

Lab 13 – The Mars Lab Tutorial

Materials Needed: The Mars Lab utilizes four Shaded Relief Maps (MC-7, MC-15, MC-19, and MC-25)
prepared from the Mariner 9 Mission to Mars by the USGS. You will begin with MC-25. The Mars
Worksheet will utilize additional USGS maps of Mars. You will obtain these maps from
https://astrogeology.usgs.gov/search?pmi-target=mars. Use the filters as shown below and do not use
the revised version, but the original version:

INTRODUCTION – The Mars-like Planet

The large number of craters on Mars reminds us of the Moon and Mercury. But the sand
dunes, volcanoes, and dry river valleys remind us of processes found here on earth.
Indeed Mars is in many ways a halfway planet; it has a surface much less active than the
direst desert on earth, yet it seems like a tropical wet-house when compared to the bare
and dry surfaces of Mercury and the moon. But in addition, Mars is also a world of its
own. The great volcanoes, chasms, and dune fields of Mars are unlike anything found on
earth or the other planets. In the final analysis, Mars is more like Mars than anyplace else.

In this lab, you will sample some of the diversity of Mars by examining some maps of
various regions on Mars. These maps include several regions selected from the
Atlas of Mars by Batson, Bridges & Inge. Of course, a complete survey is out of the
question in such a short time, but as you work through the worksheets provided, we hope
you will appreciate some of the surprising variety of landforms found on this bone dry
desert world. Some of the key concepts that you will explore are given below. As you

https://astrogeology.usgs.gov/search?pmi-target=mars

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read the introductory pages, please answer the questions and fill in the blanks by using
the provided maps.

I. IMPACT CRATERS AND STRUCTURES

During the past 4.5 billion years, countless tiny, small, medium, large and enormous
meteoroids have struck the surface of Mars. As on the other terrestrial planets, there are
small impact craters, medium-sized impact craters with central peaks, multi-ring
structures and large basins – all due to the influx of impacting meteoroids and asteroids.
However, these craters have been subject to much more wind and water erosion than
craters on the moon or Mercury. In the Thaumasia Quadrangle (MC-25) are examples of
several varieties of impact craters. Most of the moderately large craters are named
whereas the smaller craters are designated by letters.

1. Please record the names and diameters of the following medium-sized craters found

at the designated positions:

Name Latitude Longitude Size (km)

_______________ -51 S 113 W _______________
_______________ -47 84 W _______________
_______________ -52 70W _______________

Use the scale at the bottom of the map to determine the diameters. Notice that the interior
of these craters are relatively smooth. Winds have smoothed the interiors of many
Martian craters.

2. What is the name and diameter of the large crater at longitude 82°W and latitude

-53°S?

______________________ (82°W -53°S) ___________________ km

What is unusual about this crater? ____________________________________________

Smaller Craters and Central Peaks
The first letter (capitalized) for the smaller craters is assigned in terms of increasing
longitude (to the west and right) and the second letter is assigned in terms of increasing
latitude (to the north and up). Several of the smaller craters have small central peaks –
mountains that were thrown up in the center of the impact crater when the craters were
formed. Give the latitude, longitude, and diameter of these four craters:

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Name Latitude Longitude Size (km)
Xp __________ S __________ W ___________
Wpd __________ S __________ W ___________
Vx __________ S __________ W ___________
Aka __________ S __________ W ___________

You may have noticed that these small craters are not really small. While all such craters
do not have central peaks, many of them do. The peaks can be further studied to give us
more information about the energy of the impacting asteroids and the strength of the
Martian rock layers.

Between Latitudes 40 to 48 South and Longitudes 100 to 110 West, is a large smooth
roughly circular basin. This may be the mark of a very large and ancient impact structure
that has since been filled with lava and/or dust and eroded by water and/or winds.
Whether this is true in this particular case would require additional study. What is the
name of this large planum? _____________________________________ Planum

Relative Age
One of the craters labeled “Pg”, (latitude 56.5°S, longitude 93°W) has a small interior
crater, Pgc. It is obvious that Pgc is younger than Pg. the same principle can be used for
overlapping carters. In these cases a younger crater has partially obliterated an older
crater’s rim. Use this principle to determine which crater is older; Wq or Xq (~ 43°S,
112°W). ____________

II. VOLCANIC ACTIVITY

Volcanoes
Several volcanoes on Mars are much larger than any found on earth. Their summit
calderas may be many kilometers high and their flanks sometimes extend for hundreds
of kilometers. A few scattered meteorite craters on their flanks suggest that many of them
have formed during the past few hundred million years. Here again, we see evidence that
Mars is much less active than the earth, but much more active than the moon and
Mercury.

Three very large, very ancient and very different types of volcanoes are found in the
Elysium Quadrangle of Mars (MC-15). Elysium Mons (Mons = Mountain) is a shield
volcano roughly circular with relatively smooth flanks that exude from a central vent or
central caldera. Notice that the base of the volcano reaches from 209-217°W. A slightly
smaller mountain, which has a larger caldera, is Albor Tholus, centered at approximately
19°N, 210°W. A tholus is an isolated dome shaped hill or mountain. What are the
diameters of these two huge mountains and their central calderas?

Base Diameter Caldera Diameter
Elysium Mons ________________ km ________________ km
Albor Tholus ________________ km ________________ km

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Caldera
After a period of volcanic activity the magmatic pressure which caused the volcano
begins to subside. Sometimes the pressure drops so much that the center of the volcano
collapses. This central crater is called a caldera. The caldera is different from an impact
crater is several ways, some of which you will discover by observation during this lab.
Two important differences are the lack of central peaks (sometimes found in impact
craters, but never found in calderas) and the lack of an uplifted rim around a caldera. The
rim of an impact crater is made of overturned rock.

Look carefully at the differences between the flanks and the calderas of the two large
volcanoes and the rims and interiors of the impact craters Eddie (12°N, 218°W), Lockyer
(28°N, 199°W), and Wg (8°N, 219°W). The impact craters generally have raised rims
and sometimes have central peaks. The volcanoes never have central peaks. At 3°N,
196°W is a nearly buried feature labeled “Jc”. Is Jc a relic impact crater or volcano?____

Patera
A complex or irregular volcanic crater is called a patera. A large, ancient volcanic
structure is found in the Elysium quadrangle (15°N, 181°W).

III. RUNNING WATER

Most of the surface of the Margaritifer Sinus quadrangle (MC-19) is very ancient.
Ancient craters that are believed to be perhaps three billion years old clutter the surface
of the region. In addition, however, there is also evidence of ancient beds of running
water in the Margaritifer Sinus quadrangle. For example, what is the name of the valley
that flows to the northwest from the edge of the map up into the Holden crater (26°S,
34°W)? _________________________________________

Notice that the vallis is quite different from the nearby Erythrea Fossae. The fossae are
believed to be rifts (pulled apart by rock movements – tectonics instead of erosional
features). What is the valley south of Jones crater (20°S, 20°W)? __________________

Note that the valleys look like tree branches (so called dendritic forms) where smaller
tributaries have run into larger streams. Additional forms are also in evidence. What is
the name of the chasm in the northwest corner of the map? __________________ Chasm

What are the names of the two chaotic tumbled regions in the northernmost regions of the
map? ___________________ Chaos and ______________________ Chaos. Chaotic
regions may be due to underground water and/or moving ice.

IV. EROSION, WATER, WIND, AND ICE

Polar Regions
Both poles of Mars are covered with frost, snow, and ice due to both carbon dioxide and
water. The poles wax and wane with the seasons being larger during their respective
winters and smaller during their respective summers. They also exhibit evidence that
Mars may have had its own ice ages and warm ages over the past thousands and millions

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of years. Some of the sand dune fields near the poles are larger than any others known in
the solar system.

A Very Martian Landscape
The Cebrenia Quadrangle (MC-7) of Mars offers a very Martian landscape. Can you
recognize these features?

Name Diameter
1 A moderately large impact crater in the

middle of the map? [48°N, 220°W]

__________________ _________ km

2 A very large volcano at the bottom of
the map?

__________________ _________ km

3 An ancient valley slightly to the SW
[40°N, 225°W; 35°N, 220°W]

__________________ Vallis

4 An ancient, fairly straight fault near the
above Vallis? __________________ Fossae

What is unusual about the craters Tyndall (Dg), El (46°N, 191°W) and the unnamed
crater centered near 32°N, 188°W? ___________________________________________

________________________________________________________________________

Pedestal Craters
In the northwest portion of the map are some curious craters that seem perched upon
domical hills. These strange features were apparently formed from impacts that melted
enormous amounts of ice frozen in the ground.

Name (Label) Lat Long Name (Label) Lat Long
__________________ 56°N 220°W __________________ 63°N 228°W

Aeolian or Wind Erosion
Sand dunes, bright and dark windblown streaks, hundreds of kilometers in length, and
wind filled valleys and craters offer plentiful evidence that Martian wind affects the
surface of Mars. Do you see any features on MC-17 or MC-15 that are due specifically to
the action of the wind? _____________________________________________________

________________________________________________________________________

________________________________________________________________________

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When you have completed your tutorial, check the key to verify your answers. Your
answers should be accurate to approximately 15% or better. If most of your answers are
correct and if you understand any errors that you might have made, you are ready to
proceed to the graded worksheet.

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BIBLIOGRAPHY
[Introductory, Semi-technical & Technical]

Baker, Victor R. (1982). The Channels of Mars. University of Texas Press.

Batson, R.M., Bridges, P.M. & Inge, J.L. (1979). Atlas of Mars (NASA).

Beatty, J.K. (Sept 1976). “Viking Lands on a Very Red Planet”, Sky and Telescope v.
52.

Beatty, J. Kelly (Dec 1976). “Vikings Rest During Mars’ Conjunction”, Sky and

Telescope vol. 52, #6, pp. 404-409.

Beatty, J.K., O’Leary, B., & Chaikin, A. Eds. (1990). The New Solar System (3ed). Sky

Publishing Corp.

Carr, Michael (1981). Surface of Mars. Yale University Press.

Carr, Michael (1996). Water on Mars. Oxford University Press: New York. 239 pages.

Kiefer, H.H., Jakosky, B.M., Snyder, C.W., & Matthews, M.S., Editors (1992). Mars.

University Press of Arizona Press: Tuscon.

Masursky, Harold (Aug 1972). “The New Mariner 9 Map of Mars”, Sky and Telescope

vol. 44, #2, pp. 77-82.

Weaver, Richard F. (Feb 1973). “Journey to Mars”, National Geographic Magazine vol.

143, #2, pp. 231-263.

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Name _________________________________ Date ________________
Section _________________________________ Score ________________
Partner _________________________________ I.I’s ________________

Lab 13 – The Mars Lab Worksheet

Materials Needed: You will need the Topographic Maps of Tharsis Quadrangle (MC-9), the Oxia Palus
Quadrangle (MC-11) and the Coprates Quadrangle (MC-18) as well as the Controlled Photomosaic and
Topographic Maps of the Tharsis Northwest Quadrangle (MC-9NW). Note that you will be using three
separate maps of the Olympus Mons region.

Grading Notes: Several times you will be asked an open-ended question requiring more than a simple
name, number, or a yes or no. Do not leave these questions blank. These questions are graded generously –
unless you fail to answer them. Questions that require written answers will count twice as much as other
questions.

I. MORE ON CRATERS

The regions we shall examine in the Worksheet portion of the Mars Lab are not as
heavily cratered as some of the regions examined in the Tutorial. This is because the
regions we shall examine in the Tutorial have been greatly altered by wind, rain, ice, and
volcanism. Even within these quadrangles, however, there has been a great deal of variety
in erosional processes. These variations in crater density tell us a great deal about the age
of the features being examined. Regions that have a low crater density are younger than
the regions that have been extensively cratered. Furthermore, regions that have many
small craters are more likely to have a few large craters.

Variations in Crater Density (MC-9, MC-11, MC-18)
Several regions have been selected from these quadrangles that represent some of the
range in crater density found on Mars. Examine the following regions and determine the
approximate number of craters in each 5° x 5° region: (Count unlabeled and labeled
craters – be attentive, a careful examination reveals a surprisingly large number)

Between 25° & 30°N and 115° & 120°W (MC-9)
____________ less than 10 _________________ 11-30 ___________ more than 30

Between 5° & 10°S and 70° & 75°W (MC-18)
____________ less than 10 _________________ 11-30 ___________ more than 30

Between 5° & 10°N and 40° & 45°W (MC-11)
____________ less than 10 _________________ 11-30 ___________ more than 30

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Give the name and size of the two largest impact craters on MC-11:
Name __________________________________ Diameter _________________ km
Name __________________________________ Diameter _________________ km

Give the name and size of the two largest impact craters on MC-18:
Name __________________________________ Diameter _________________ km
Name __________________________________ Diameter _________________ km

Give the name and size of the largest impact crater* on MC-9:
Name __________________________________ Diameter _________________ km
*It is not Uranius Patera – Uranius Patera is volcanic.

Which Quadrangle is the most heavily cratered? How so?

Does the Quadrangle with the most craters have the largest craters? Explain your answer.

Many astronomers and geophysicists believe that perhaps three or four billion years ago, there were
probably ancient rivers on Mars. After Mars began to dry up and cool off, there were apparently occasional
floods due to widespread melting – perhaps during volcanic eruptions and/or due to impacts from relatively
large asteroids and comets. The large and now dormant volcanoes on Mars, particularly those in the Tharsis
region, have apparently erupted during the past billion years and thus the volcanic features are much
younger than the features due to water erosion. Wind erosion, however, continues into the present. Are the
features on your charts consistent with these ideas? Can you give specific examples? Some ideas to keep in
mind: (1) whenever there are few craters, the surface is relatively young, (2) large impacts are rare, (3) the
terrain around the ancient riverbeds is much more heavily cratered than the terrain around the large
volcanoes, and (4) while not evident here, windstorms on Mars are so widespread that they can sometimes
be observed from earth.

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II. VOLCANOES

For this portion of the lab, you will need to examine the topographic map of the Tharsis
Quadrangle (MC-9). Later, you will examine one of these giant volcanoes (Olympus
Mons) in more detail by using some more detailed maps of the Northwest quadrant (MC-
9NW)

Volcanoes: Sizes and Elevations – Volcanoes of the Tharsis Bulge

What are the diameters of:
Ascraeus Mons ___________ km Bibles Patera ___________ km
Ceraunius Tholus ___________ km Olympus Mons ___________ km
Pavonis Mons ___________ km Uranius Mons ___________ km
Uranius Patera ___________ km

[The entire mountains, not just the calderas.]

The largest volcanoes on the earth are approximates the size of Biblis Patera and Uranius
Tholus – the smallest of these seven structures. These volcanoes are also very high.
Check the red topographic contours to determine their elevations.

What is the highest elevation found on Olympus Mons? ____________ km
What is the highest elevation found on Pavonis Mons? ____________ km
What is the highest elevation on Ascraeus Mons? ____________ km

What is the name of the volcano with the largest Caldera? (It is not Olympus Mons)
How large is this caldera?
Name ___________________________________ diameter ________________ km

A caldera is a larger crater caused by sinking of the central region of a volcano after the pressure of the
outflowing magma begins to decrease. The calderas at the summits of Martian volcanoes are very similar to
those of some terrestrial volcanoes except that the Martian volcanoes and calderas are sometimes much
larger. However, the Martian volcanoes frequently exhibit additional cratering found on their flanks that are
due to meteoroidal impact. These impact craters often give us a way of crudely estimating the volcanoes’
ages. Most of the Martian volcanoes seem to be between one hundred million years and one billion years
old.

Age and Erosion of Volcanoes
Give the labels of the three largest impact craters on the flanks of Olympus Mons and the
largest impact craters on the flanks of Ulysses and Ascraeus Patera. (longitude and
latitude are provided)

Olympus Mons ______________ at 133°W 17.5°N
Olympus Mons ______________ at 132°W 18°N
Olympus Mons ______________ at 132°W 22°N
Ulysses Patera ______________ at 121.5°W 4°N

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Ascraeus Patera ______________ at 101.5°W 12.5°N

What evidence is there that crater MC-9 Sc is younger than Ulysses Patera?

What evidence is there that the impact crater on the northern edge of Ceraunius Tholus
struck before Ceraunius Tholus became extinct?

Close-up of Olympus Mons – you will need both the Controlled Photomosaic and the
Topographic Map of the Northwest (NW) section of the Tharsis Quadrangle for this
section (MC-9NW).

The sunken central caldera of Olympus Mons is found at approximately 133°W, 18°N in
the SW portion of the Controlled Photomosaic. Notice how the flows seem to have flown
out in all directions from these central vents. What is the longest diameter you measure
for the caldera? ___________________ km

Several small craters on the flank of the Olympus Mons are not visible in the larger
quadrangle map. Give the size and coordinates of three of them. A magnifying glass may
help.

Size Coordinates Size Coordinates Size Coordinates

___ km _____________ ___ km _____________ ___ km _____________

To the north of Olympus Mons is an enormous lava field that actually extends beyond the SW portion of
the quadrangle. Note again that there are few impact features, making this a very young surface for Mars.
Still, if you look carefully you will generally find some more small impact craters on the flanks of most
volcanoes. This tells us that even though the volcanic regions are much younger than much of the Martian
surface, nevertheless, they have ages in the millions of years. It is not every day that a 5-20 kilometer
impact crater is formed.

What is the altitude at the top edge of the steep edge of the eastern flank (around
129.2°W, 17.5°N) of Olympus Mons? ___________ km or ____________ m

[1 km = 1000 meters – your answers should be greater than 20km or 20,000m]

What is the altitude at the bottom edge of the steep edge of the eastern flank (around
129.2°W, 17.5°N) of Olympus Mons? ___________ km or ____________ m

So, how far from the top to bottom for these cliffs on the east flank of Olympus Mons?
___________ km or ____________ m

[While the cliffs are not nearly as high as the summit of Olympus Mons, they are higher than many high
mountains on earth.]

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III. CHASMS AND VALLEYS

Valles Marineris
The Coprates Quadrangle (MC-18) has one of the longest known valleys in the solar
system. The valley has been formed from a large rift near the equator of Mars which has
been further eroded by wind and water. The valley actually extends beyond the picture
here. How wide is it at its widest point (Melas Chasma)? (Ignore the extra tributary) ____ km

Using the topographic contours, how much depth is there between the highest rims near
Ius Chasma (to the west) and the lowest points in the valley near Eos Chasma (to the
east)?

Highest rim elevation _________________ km
Lowest valley elevation _________________ km
difference _________________ km

It you look very carefully, a few craters can be found in the valley itself. There are many
more impact craters to the north and south of the valley than in the valley itself. This tells
us that the floor of the valley and quite possibly the valley itself is much younger than the
surrounding plains.

On the photographs, there is not much evidence of running water. However, there is
evidence of several enormous landslides. For example, how high are the cliffs at Melas
Chasm (in the central regions of the valley)?

top = ________ km bottom = _______ km total drop = _________ km

IV. RUNNING WATER

In the Oxia Palus Quadrangle (MC-11) we find a different form of valley. The crater at
3°N and 16°W seems to be the starting point for a flood that tore toward the Chryse
Planitia.

What is the label of the crater? ______________________________________________

What is the name of the valley? _____________________________________________

How does the topography support this hypothesis? (Hint – note the elevation of the
Chryse Planitia, negative numbers are below mean elevation)

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Are the valleys in the Southwest of the map such as Shalbatana Vallis and Simud Vallis
consistent with the idea that liquid material (presumably water) once flowed into Chryse
Planita? Explain.

What are the names of the odd landforms found at the head of Tiud Vallis and Simud
Vallis?

These odd landforms may be due partially to the collapse of regions that experienced catastrophic melting
of enormous quantities of frozen ice. Whatever their source, these features remind us that there is a great
deal about Mars that we do not understand.

After completing the worksheets, submit them to your instructor.

Name _________________________________ Date ________________
Lab 13 – The Mars Lab Tutorial
Name _________________________________ Date ________________
Lab 13 – The Mars Lab Worksheet

1

Name _________________________________ Date ________________

Section _________________________________ Score ________________
Partner _________________________________ I.I’s ________________

Lab 16 – Classification of Galaxies and Galaxies in Color

Materials Needed: Provided in the lab: the Hubble Atlas of Galaxies
(http://shelf2.library.cmu.edu/Tech/00537465 ), Hubble Key:

Figure 1 Hubble Key (Wiki)

Objectives: To become familiar with the basic Hubble system for galaxy classification
and their colors. This exercise provides background information for the lectures,
identifies characteristic features for telescopic observations, and in addition, allows the
student a firsthand look at photographs that are part of every night life of professional
astronomers.

INTRODUCTION

http://shelf2.library.cmu.edu/Tech/00537465

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Galaxies are enormous collections of stars containing billions and even trillions of stars.
Our sun is part of a galaxy that we sometimes call the Milky Way Galaxy since the
center of our galaxy is towards the middle of the Milky Way. All the stars that we can see
with our naked eyes are part of our galaxy. Indeed, there are only three galaxies besides
our own that can be seen with the naked eye. The Andromeda Galaxy, the largest
nearby galaxy, appears as a faint smudge on a clear night to persons with good eyesight.
In the Southern Hemisphere we can also see two faint, misty objects called the
Magellanic Clouds. They are two minor satellite galaxies of our galaxy. With large
telescopes, however, these and many other faint, nebulous objects reveal themselves as
vast systems of star far beyond the Milky Way. In this exercise, we will first examine
some photographs from the Hubble Atlas of Galaxies, the standard reference for galaxy
classification. As a sequel to this exercise, you may wish to examine some of the color
photographs of the Wray Color Atlas of Galaxies (Lab 17), the CD ROM images from the
Malin Galaxy Collection (Lab 19), or look at some fainter images of more distant
galaxies found on the Palomar Sky Survey Prints. The Hubble Space Telescope (Lab 20)
also includes some unusual galaxies in its collection of images. The internet also offers
some interesting possibilities.

Basic Distinction: Spirals and Ellipticals
All galaxies do not look alike and so astronomers generally classify them according to a
scheme first developed in detail by William Hubble. According to this scheme, most
galaxies are classified as being either spirals or ellipticals. Spirals are galaxies with
swirling arms containing billions of stars apparently whirling about the centers or nuclei
of the galaxies. The nearest large galaxy, the Andromeda Galaxy or M31, is a spiral
galaxy as is our own galaxy, the Milky Way. Ellipticals are galaxies whose images have
an elliptical outline. Ellipticals appear rather featureless at first glance, but some
ellipticals are quite unusual. Some giant ellipticals contain perhaps as many as a hundred
times as many stars as our own galaxy. One of the galaxies that you will examine in this
exercise, M87 is such a giant galaxy. Most astronomers also believe that M87 has a
massive black hole at its center. [Not from these photos, however.]

Spiral galaxies are associated in the public’s mind with galaxies partially because of their
spectacular arms which makes their pictures so stunning. Besides the Andromeda galaxy
there are many other picturesque galaxies such as M51, the Whirlpool galaxy, and M104,
the Sombrero galaxy. If we look at them more closely, we will find that some of them are
more closely wound up than others. In addition to the arms, we also find that spirals also
have a central bulge of stars that is not part of the spiral arms. The tightly wound spirals
normally have a large central bulge and are called Sa galaxies. The loosely wound or
open spirals with small central bulges are called Sc galaxies. Type Sb spirals, of course,
are in between. Our galaxy is probably an Sb galaxy. We will use the Hubble Atlas to
acquire some familiarity with these principles. Your Hubble Key also illustrates these
features with a sort of visual shorthand.

Spiral galaxies contain large amounts of dust and gas as well as stars. Indeed, the arms
are so spectacular primarily because young, hot blue giants are formed out of the dust and
gas. One reason it took astronomers so long to recognize that we are inside a galaxy is
precisely because our galaxy is a spiral; the dust of our galaxy makes more than half of

3

the stars of our galaxy invisible even in the larges telescopes. Even when we have a very
faint image of a spiral galaxy, we can still recognize the spiral by its clumpy blobs of dust
and gas. This will be very important when you look at some of the faint images on the
Sky Survey Print.

Ellipticals are much “smoother” in appearance than spirals. They seem to be composed
primarily of very old stars and have very little gas. The only prominent difference
between them is in the degree of flattening of the image. A nearly circular image is
characteristic of an E0 galaxy; the most elongated image is characteristic of an E

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galaxy. Again, the intermediate types are labeled E1 through E6. You will see numerous
examples throughout the exercise. The basic scheme is also shown on the Hubble Key
(provided in the lab).

Oddballs: Barred Spirals, Intermediate Types, and Irregulars
While these general principles apply to most galaxies, there are a number of interesting
complications. Some spiral galaxies have a long linear or barlike feature in their central
regions. These galaxies are called barred spirals or SB galaxies. SB galaxies are
classified exactly like other spirals. SBa galaxies are barred spirals with very tightly
bound arms and larger central bulges. SBc galaxies are barred spirals with open arms and
small central bulges. Again, the SBb galaxies are an intermediate type of barred spiral.
Some galaxies are, of course, halfway between elliptical and spirals. Such galaxies are
too smooth to be spirals and too dusty to be ellipticals. These intermediate types of
galaxies are called S0 galaxies. They sometimes show a disk, but they do not possess
“arms”. Galaxies that are smooth, but not rounded or elliptical in shape or outline are
frequently S0 galaxies. Finally, it should be noted that even this modified scheme works
only for about 95% of the galaxies. Galaxies, which do not fit any classification scheme,
are called irregular or Irr galaxies. Two nearby irregular galaxies are the Large
Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). Naturally enough, the
irregulars include some of the most interesting galaxies. In this introductory exercise we
will not emphasize the SB’s, the SO’s and the Irr’s, but we will examine a few of these
oddballs.

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ADDITIONAL READING

[Any astronomy textbook has additional information about galaxies and their classification. An especially
good treatment can be found in Robbins & Jefferys Discovering Astronomy. Frequent articles of interest

are found in Astronomy, Sky, and Telescope and Scientific America.]

Ira Sprague Brown (Aug 1955). “Completing the Atlas of the Universe”, National

Geographic Magazine vol 108, #2, pp 185-190.

Timothy Ferris (1982). Galaxies. Stewart, Tabor & Chung: New York, 1982. 192 pages.

[a stunning collection of beautiful color photographs and non-technical excellent prose]

Alan Hirshfeld (April 1980). “Inside Dwarf Galaxies”, Sky and Telescope vol 59, #4, pp

287-291. [small is also interesting]

Edwin P. Hubble (1958). The Realm of the Nebulae. Dover: New York.

[a reprint of Hubble’s 1936 classic]

Allan Sandage (1961). The Hubble Atlas of Galaxies. Carnegie Institute of Washington:

Washington, D.C.
[the lab’s primary source]

Ronald A. Schorn (Jan 1988). “The Extragalactic Zoo – I”, Sky and Telescope vol 75, #1,

pp 23-27.

Raymond Talbot, Eric Jensen & Reginald Dufour (July 1980). “Anatomy of a Spiral

Galaxy”, Sky and Telescope vol 60, #1, pp 23-28.

Sidney Van Den Bergh (Dec 1976), “Golden Anniversary of Hubble’s Classification

System”, Sky and Telescope vol 52, #6, pp 410-414.

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PART I: Galaxy Classification

I. Getting Acquainted with the Hubble Atlas [Tutorial Worksheet]
Open the Hubble Atlas from the link above. The name of the galaxy is either the page
before of after each image page. The list of galaxies by NGC (New Galactic Catalogue)
number is after the introductory pages.

II. Classifying Large Images (from the Atlas) [Individual Worksheet]
You will apply your newly learned information to the task of classifying the additional
galaxies listed at the beginning of your individual worksheet. This will provide you with
a little more practice. A suggested procedure:

(1) First classify each galaxy as either elliptical (E) or spiral (S).
(2) Using the Hubble Key, determine whether the elliptical is an E0, E1, E2, E3,

E4, E5, E6, or E7.
(3) For the spirals, determine whether they are Sa, Sb, or Sc. Be sure to account

for the tilt of the spiral.
(4) Decide what to do with the oddballs. Some spirals have a bar (SB). One or

two galaxies may be intermediate between spiral and elliptical (SO). Real
oddballs are called irregulars (Irr).

After you complete the worksheet, you will turn in your results. If you have done well
you will receive full credit. If not, you will normally still receive partial credit. If you are
careful, your results should be quite satisfactory.

TUTORIAL: USE THE HUBBLE ATLAS

Elliptical Galaxies
M87: The Nearest Giant Elliptical or NGC 205: The Nearest Elliptical

First, look carefully at either NGC 4486 (M 87) or at NGC 205. Notice how smooth the
general distribution of light is. Does the galaxy in your Atlas have a sharp edge?
___________________________________ (#1)

M87 is an unusual elliptical galaxy containing approximately a trillion stars; NGC 205 is another smaller
but much closer elliptical galaxy. No individual stars may be seen in the photograph of M87 and only a
very few are seen in the photograph of NGC 205. The galaxies are too far away for that. Both photographs
are “cluttered” by a number of foreground stars from our own galaxy that just happen to be in the same
general direction. Many of the larger stars have a diffraction pattern with four spikes. Most galaxies are
elliptical galaxies and most elliptical galaxies are smaller than NGC 205, which itself has a stellar
population perhaps a hundred times smaller than that of our own galaxy. A typical dwarf elliptical (Leo II)
is also found on page B1. The very largest galaxies are generally giant ellipticals such as M87.

The hundred or so small soft dots that seem to be part of the M87 galaxy are not
individual stars but globular clusters – groups that may have as many as one hundred
thousand stars. Do you see the 7 or 8 satellite galaxies? __________________________

Several additional elliptical galaxies listed below. These are fairly typical ellipticals.
Except for a few overexposed central regions, their images are very regular and smooth.
Their primary distinguishing characteristic is their shape – from circular (E0) to highly

6

elongated ellipses (E7). Use your Hubble Key and attempt to classify the following
elliptical galaxies of your Atlas as either E0, E1, …. or E7:

NGC 4406 (M86) ________ NGC 751 ________

NGC 205 ________ NGC 4636 ________

NGC 4486 (M87) ________ NGC 4697 ________
Actually, M87 is a little peculiar, probably due to a massive black hole near the center of the galaxy. The
peculiar feature may be seen on B6 and in recent HST photos.

Large Spiral Galaxies
M31: The Andromeda Galaxy, Our Nearest Spiral Neighbor or M81: A Large Nearby
Spiral Galaxy

Now let us look at either the Andromeda Galaxy (M31, NGC 224) in the constellation of
Andromeda or at NGC 3031 (M81), another large spiral galaxy found in the constellation
of Ursa Major. M31 is the nearest large spiral, about 2.5 million light years from the sun;
M81 is slightly further away, about 10 million light years from the sun. The spiral arms
are part of a somewhat flattened collection of stars, gas and dust that form a disk. Do the
arms reach all the way to the galaxy core?

Can you see some of the very faint extensions of the arms into the darker regions? The
pictures are actually somewhat misleading; radio observations reveal that the galaxy
actually reaches about two or three times as far into space as the apparent visible edge
suggests. Notice too that M31 has two fairly impressive satellite galaxies. The small
galaxy to the lower right of M31 is NGC 205.

Ellipticals versus Spirals
Comparing M31 & M87 or M81 & NGC 205

What are the most obvious differences between the above spirals and ellipticals in your
Atlas?

Which type of galaxy is marked by prominent dark streaks or lanes due to dust, the spiral
or elliptical? ________________________________________________________ (#2a)

Does the core or central bulge of your spiral galaxy most resemble the outer regions of
your spiral or the central regions of the elliptical? Hint – is it smooth or does it have large
clumpy regions of dust and gas? ________________________________________ (#2b)

Spirals: Sa, Sb, Sc; Open Spirals and Tightly Wound Spirals

7

Spirals display a little more variety than ellipticals. Part of the variety comes from
differences both in the arms and in the central regions. Also, because of the obscuring
material in the dark dust lanes, spirals may look quite different when observed from
different viewing angles. The most tightly wound arms belong to the Sa spirals; the most
loosely wound or open arms belong to the Sc spirals. Sb spirals have characteristics
intermediate between Sa and Sc galaxies. First, let us compare a typical Sa with a typical
Sc.

NGC 4274 Sa NGC 3898 Sa
NGC 5457 (M 101) Sc NGC 5194 (M 51) Sc

Does the Sa or Sc galaxy have the tightest arms? ___________________________ (#3a)
Does the Sa or Sc have the largest central bulge (allow for the photo size)?
___________________________________________________________________ (#3b)

You will find that this is a general rule – large central bulges are almost always found
together with tight arms in Sa galaxies; while very open arms and small bulges are found
together in Sc galaxies.

If NGC 4274 is an Sa & M101 is an Sc, what is M31? ____________________________
If NGC 3898 is an Sa & M51 is an Sc, what is M81? _____________________________

Edge-on Spirals
Most of the photographs of galaxies that we have been examining so far have been
viewed “face on”, that is, we view from a perspective that allows us an immediate
inspection of their arms and central regions. Sometimes, though, we see galaxies “edge
on”. In this case we generally cannot see the arms. Instead, what we see are primarily
dust lanes. However, we can determine the size of the central bulge – and that is
generally enough to classify the galaxy. Can you classify the galaxy (or galaxies) in your
set by comparing the size(s) of the bulge and the arms?

NGC 253 _________________________________________________

Which galaxy is an Sb and which an Sc? NGC 4565 ____________ NGC 5907 ________

Notice that the outline of NGC 253 looks something like that of an elliptical galaxy. However, an elliptical
galaxy would have no dark dust lanes.

Subtleties I: Intermediate Type of Galaxy or SO Galaxies
The more closely we look at anything the more complicated it seems. Some galaxies are
truly borderline cases. Galaxies that do not quite fit the simple scheme developed so far
are NGC 5866 and NGC 1201 & NGC 7457 . While they are too irregular and/or too
flattened in shape to be elliptical and may even have a disk structure, they lack the arms-
and-dust of true spirals. We classify such borderline galaxies as SO galaxies.

Subtleties II: Barred Spirals or SB Galaxies

8

Some spiral galaxies have large concentrations of stars that form a more or less
rectangular outline. Such concentrations are called bars – and spiral galaxies with such
bars are called barred spirals or SB galaxies. NGC 1398 & NGC 1300 are examples of
such SB galaxies. Since both of these galaxies have medium size bulges both are
classified as SBb’s. The big B is for the bar; the little b is for the medium bulge as with
normal spirals. Classify your other SB galaxy as either SBa, SBb, or SBc.

NGC 4394 __________________ NGC 1073 ______________________

Subtleties III: Irregular Galaxies or Irr Galaxies

Find the three pictures of NGC 3034 (M 82), a galaxy apparently disturbed by violent
starburst activity – intense movements of gas and dust due to the infall of huge gas clouds
into the denser central regions of the galaxy. It is truly an irregular galaxy or Irr galaxy.

Find the picture of the Large Magellanic Cloud (LMC), a small satellite galaxy of our
own galaxy. The two Magellanic Clouds are the closest external galaxies but cannot be
seen in most of the Northern Hemisphere since they are close to the South Celestial Pole.
Galaxies without obvious structures and/or violently disrupted galaxies are called
irregular or Irr galaxies.

Practice: Since you will be graded on this exercise, it will probably help to have a dry
run before doing your individual worksheets. See if you can classify the following
galaxies in the appropriate set.

Galaxy Type Galaxy Type

Sextans ________ NGC 628 (M 74) ________

NGC 598 (M 33) ________ NGC 185 ________

NGC 4736 (M 94) ________ NGC 891 ________

NGC 3368 (M 96) ________ NGC 2525 ________

NGC 3377 ________ NGC 2681 ________

NGC 4762 ________ NGC 3329 ________

NGC 7331 ________

NGC 7332 ________

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PART II: Galaxies in Color

1) Open http://skyserver.sdss.org/dr13/en/proj/advanced/galaxies/spectra.aspx and click
on each of the galaxies in the table about mid page. You will receive this image:

2) Note the galaxy name, redshift, and type in the table below:

http://skyserver.sdss.org/dr13/en/proj/advanced/galaxies/spectra.aspx

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Name Galaxy Type Redshift Spectra Shape
(Flat or
Curved?)

Distance of K
and H line
(How many
tick marks
from 4,000
Angstroms?)

3) Click on the spectrum and note if the spectrum is flat or curved and how many ticks
the K and H lines are from the 4,000 Angstrom lines in the table above. The spectrum
looks like this:

11

4) Answer the following questions:

• Is there relationship between spectra flatness and galaxy type?

• Is there a relationship between number of tick marks and redshift?

Name _________________________________ Date ________________
Lab 16 – Classification of Galaxies and Galaxies in Color

Distances to Clusters – 1

DISTANCES TO CLUSTERS

Purpose: To study Hertzsprung-Russel diagrams and see how we can find the
distance and age of star clusters.

Introduction:
Star clusters provide a laboratory for studying stars. We can learn about the
distance, color, and evolution of stars. Because the life spans on stars are so long
compared with human life spans, we must look at the stars as they exist today. Then
by looking at several different stars, we can classify these stars like we classify a group
of people. Some people have wrinkles and are stooped. We tend to call these people
old. Some people have smooth skin and are upright. We call these people young.
We can do these things with stars. Some are large and red. These are older stars
called giants. Some stars are bright and blue. These are the younger stars. This is
the science of population study. If the population contains older people/stars than
younger people/stars we called the group/cluster old. If the population contains the
reverse population, we call the population young.
We tend to want to study these populations as close to each other because
outside effects tend to skew your results. In the case of people, effects like birth rates
and sun exposure could make the population seem younger (in the case of increased
birth rates) or older (in the case of increased sun exposure). Therefore you pick your
population clusters in close proximity to each other so that the conditions are the
same. We use the same principal with the star cluster. Because we know they were
the born the same time, we do not worry about the birth rate issue with stars. Since
they are at the same distance we can ignore reddening within the cluster so we don’t
worry that different stars are looking older than their true age, we only have to worry
about the reddening between us and the cluster. When light travels through dust some
of it can be scattered causing the light to look redder, thus older.

In this lab, we are going to look at the magnitude (brightness) of stars in the
cluster and use this to tell us about the age of the cluster and the distance of the
cluster. We will do this through a program called AstroImageJ, an image processing
program. We will find the magnitude of the stars in two different filters, the red (R)
and green (V). Then we will find the color magnitude diagram, a diagram similar to
Hetzsprung-Russel diagram. We will then find the age and the distance of the cluster.

Distances to Clusters – 2

Figure 1 a Hertzsprung-Russel Diagram and Stellar Isochrones (Wiki)

Distances to Clusters – 3

Part I: AstroImageJ

1) Down AstroImageJ from
https://www.astro.louisville.edu/software/astroimagej/installation_packages/.
For mac download the x64_mac package and unzip into your applications
folder. For pc download x64_windows and unzip into your programs folder.
Follow any instructions from your instructor for further information.

2) Download Cluster Charts from D2L from Laboratory Manual >> Distance to
the Clusters. Your instructor will assign your group a cluster, download R.fit
and V.fit for your cluster to your computer.

3) Open AstroImageJ. The window should look like this:

4) Open the R.fit and V.fit file for you cluster using the File >> Open from the
Main Menu. You should have two image windows that look like this:

5) Flip each image on the image windows using View >> Invert Y to align with the
Cluster Chart for your cluster.

https://www.astro.louisville.edu/software/astroimagej/installation_packages/

Distances to Clusters – 4

6) Select Analyze >> Multi-aperture on the image window. The dialogue box
should look like:

7) On the dialogue box that pops up enter 6, 8, and 10 in the first three boxes
(object radius, inner radius, and outer radius). Select Use single step mode
checkbox to save the apertures for future images.

8) In the Cluster Charts, there are fifteen green apertures and one red apertures
for each cluster. The green apertures are the target stars and the red aperture
is the comparison star. Now click Place Apertures to start the process.

9) Left click on the first star (any green star) to create a target. Now use Shift-
Left Click to place the other green apertures. Now Left click to place the final
aperture which will be red. The cluster image should look like:

Distances to Clusters – 5

10) Now hit Enter to start the analysis process in which several windows will open.
The most important window is Multi-Plot Reference Star Settings. Click on the
Send to Multi-Aperture. Now start the analysis for the other image and click on
the first star to place the apertures for the second image. Press enter to start
the analysis for the second image. One you have analyzed the other image,
click Save to Table to save both sets of images. Here is the window:

Distances to Clusters – 6

Part II: Excel and Distances.

1) Download the Cluster Analysis excel worksheet from D2L. Open up the
worksheet and this what you see:

2) Open up the excel worksheet(s) for your clusters that received from Part I and
you should have one or two lines. Note which image each line is from. Selected
the rel_flux_T1 column for each image in the excel file and select until the you
reach rel_flux_T15 column and copy the numbers like this:

Distances to Clusters – 7

3) Now select your cluster analysis worksheet and click under either R diff or V
diff depending on the image. Now click on Paste in the upper left-hand corner
or left-click under R diff or V diff and use the Transpose function to rotate the
data from a row format to a column format. Values is another helpful option.

4) Do this for both images for each cluster (M 36, M 37, and M 38) by selecting
the tabs at the bottom of the work sheet. Once you copy this data please follow
the instructions in the image below.

5) Once you have entered the data into the worksheet please use File >> Save As
>> Save as Pdf to submit this worksheet on D2L. Only submit this with your
cover sheet, you do not need to submit the individual excel spreadsheets for
each cluster.