The Hubble Tuning Fork Diagram
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
The Hubble Tuning Fork Diagram Topic Galaxies are classified by a system designed by the astronomer Edwin Hubble (1889–1953). Introduction Classification is an important part of any field of science. Scientists classify objects into groups to make them easier to study. Any characteristic can be used to classify an object. Size, color, and shape are some of the most popular characteristics. When scientists began studying the skies with telescopes, they saw thousands of galaxies—groups of billions of stars, gases, and dust held together by gravity—in a variety of sizes and shapes. In 1962, Edwin Hubble developed a classification system for naming and describing galaxies. Hubble used the shape of each galaxy as the primary classifying characteristic. Hubble divided galaxies into three large groups based on shape: elliptical, spiral, and irregular. Elliptical galaxies have a basic circular shape but they are slightly flattened. All elliptical galaxies are designated with letter E. Within this group, some of the galaxies are more flattened than others, so he subdivided the elliptical group into eight subgroups, which he called E0, E1, E2, E3, E4, E5, E6, and E7. Galaxies labeled E0 are almost round, with very little flattening, while the E7s are very flattened and stretched out. Galaxies whose shapes are intermediate between almost round and very flattened are designated E1 through E6, depending on their degree of flattening. Hubble named the galaxies that reminded him of whirlpools or the whirling blades of pinwheels as spiral galaxies. All spiral galaxies are designated with the letter S. Hubble classified them in subgroups according to how tightly the arms are wrapped around the center or nucleus of the galaxy. Galaxies designated Sa have arms wrapped tightly around the nucleus, while those labeled Sc are less tightly wrapped; Sb galaxies are intermediate. The arms of some spiral galaxies appear to come from a bar across the center. Hubble made these barred spirals a subdivision of the © Infobase Publishing
THE HUBBLE TUNING FORK DIAGRAM 2
spiral group and labeled them SB. The arms of SBa are tightly wrapped
around the core, those of SBc are loosely wrapped, and those of SBb are
intermediate. Hubble arranged the shapes of elliptical and spiral galaxies
in a chart that shows their relationships. This chart is sometimes known
as the Tuning Fork diagram (Figure 1).
Sa Sb Sc
EO E5 SO
SBa SBb SBc
Figure 1
A lot of galaxies are not spiral or elliptical. All of these are grouped
together as irregular galaxies, and are designated as Irr. No two irregular
galaxies are alike. The ones known as Irr I galaxies are young and contain
a lot of gases, stars, and dust. Irr II galaxies appear to have resulted
from collisions of galaxies in space.
Time Required
45 minutes
Materials
✒ Figure 2
✒ access to books on astronomy or to the Internet
✒ green-, red-, and blue-colored pencils
Safety Note Please review and follow the safety guidelines.
© Infobase PublishingTHE HUBBLE TUNING FORK DIAGRAM 3
Procedure:
1. Examine Figure 2, a drawing that shows several galaxies, made from
a photograph of the night sky. Put a green circle around the elliptical
galaxies.
Figure 2
2. Compare the elliptical galaxies that you have circled to each other.
Classify the roundest one as E0 and the least round one as E7.
Classify the others somewhere between E1 and E7, depending on
how round or flattened they are.
3. Examine Figure 2 again and put a red circle around spiral and bar
spiral galaxies. Write Sa by the spiral galaxies with arms wrapped
tightly around the core and Sc beside those with arms wrapped
loosely around the core. If a spiral galaxy has a bar across it, label it
as SB instead of S.
4. Examine Figure 2 once more and put a blue circle around irregular
galaxies.
5. Using books from the library or Internet, find out the names of two
elliptical, two spiral, two barred spiral, and two irregular galaxies.
Use this information to complete the data table.
© Infobase PublishingTHE HUBBLE TUNING FORK DIAGRAM 4
Data Table
Names of Names of Names of spiral Names of
elliptical galaxies spiral galaxies bar galaxies irregular galaxies
Analysis
1. What criteria did Edwin Hubble use to classify galaxies?
2. Using galaxy shape is just one way of classifying these celestial
bodies. What other characteristic might an astronomer use to
classify galaxies?
3. In what galaxy is our solar system located? What type of galaxy
is it?
4. Spiral galaxies are believed to rotate, like the water in a whirlpool.
Based on the appearance of an irregular galaxy, do you believe that
it rotates? Explain your reasoning.
What’s Going On?
The Andromeda Galaxy and Milky Way, our own galaxy, are
spirals. The spiral structures are regions that contain many
young, hot stars that are still being formed. Some spiral
galaxies give off a diffuse blue glow, which is another
characteristic associated with young stars. Within a spiral
galaxy, stars are moving in an organized pattern of rotation.
Within the nucleus of a spiral galaxy, stars have a more
© Infobase PublishingTHE HUBBLE TUNING FORK DIAGRAM 5
reddish appearance, suggesting that they are older than the
stars in the spiral structures. Spiral galaxies are fairly
numerous and have diameters of about 70,000 light-years.
One light-year is the distance light travels in 1 year.
Elliptical galaxies include Virgo A, a central galaxy in the Virgo
star cluster; M32, a dwarf galaxy near the Andromeda Galaxy;
M110, a satellite of Andromeda Galaxy; and M87, a giant
galaxy. Diameters of elliptical galaxies range from 1/10
kiloparsecs (kpc) in the dwarfs to about 100 kpc in the
giants. One kpc equals 3,260 light-years. Elliptical galaxies
have fewer young, bright stars and more old, red stars than
spiral galaxies. The motion of the stars is more random,
showing less organized, rotational behavior.
Galaxies that cannot be described as spiral or elliptical are
classified as irregular. Sextans A, a “nearby” galaxy located
only 10 million light-years away, is one example of an
irregular galaxy. Others include the Large and Small
Magellanic Clouds. Irregulars appear chaotic, with a random
mix of dust, gases, and young and old stars. Diameters of
irregular galaxies vary from 1 to 10 kpc.
Want to Know More?
See Our Findings.
© Infobase PublishingOUR FINDINGS
THE HUBBLE TUNING FORK DIAGRAM
Analysis
1. Hubble classified galaxies based on their shapes.
2. Answers will vary. Students might suggest classifying galaxies by size
or by color.
3. Our solar system is located in the Milky Way, a spiral galaxy.
4. Answers will vary. Irregular galaxies do not appear to be rotating in an
organized fashion like spiral galaxies.
© Infobase PublishingSAFETY PRECAUTIONS
Review Before Starting Any Experiment
Each experiment includes special safety precautions that are relevant
to that particular project. These do not include all the basic safety
precautions that are necessary whenever you are working on a
scientific experiment. For this reason, it is necessary that you read
and remain mindful of the General Safety Precautions that follow.
Experimental science can be dangerous, and good laboratory
procedure always includes carefully following basic safety rules. Things
can happen very quickly while you are performing an experiment.
Materials can spill, break, or even catch fire. There will be no time after
the fact to protect yourself. Always prepare for unexpected dangers by
following the basic safety guidelines during the entire experiment,
whether or not something seems dangerous to you at a given moment.
We have been quite sparing in prescribing safety precautions for the
individual experiments. For one reason, we want you to take very
seriously every safety precaution that is printed in this book. If you
see it written here, you can be sure that it is here because it is
absolutely critical.
Read the safety precautions here and at the beginning of each
experiment before performing each activity. It is difficult to remember a
long set of general rules. By rereading these general precautions every
time you set up an experiment, you will be reminding yourself that lab
safety is critically important. In addition, use your good judgment and
pay close attention when performing potentially dangerous procedures.
Just because the text does not say “be careful with hot liquids” or
“don’t cut yourself with a knife” does not mean that you can be
careless when boiling water or punching holes in plastic bottles. Notes
in the text are special precautions to which you must pay special
attention.
GENERAL SAFETY PRECAUTIONS
Accidents caused by carelessness, haste, insufficient knowledge,
or taking an unnecessary risk can be avoided by practicing safety
procedures and being alert while conducting experiments. Be sure to
check the individual experiments in this book for additional safety
regulations and adult supervision requirements. If you will be working
in a lab, do not work alone. When you are working off site, keep in
© Infobase PublishingSAFETY PRECAUTIONS 2
groups with a minimum of three students per group, and follow school
rules and state legal requirements for the number of supervisors
required. Ask an adult supervisor with basic training in first aid to carry
a small first-aid kit. Make sure everyone knows where this person will
be during the experiment.
PREPARING
• Clear all surfaces before beginning experiments.
• Read the instructions before you start.
• Know the hazards of the experiments and anticipate dangers.
PROTECTING YOURSELF
• Follow the directions step-by-step.
• Do only one experiment at a time.
• Locate exits, fire blanket and extinguisher, master gas and
electricity shut-offs, eyewash, and first-aid kit.
• Make sure there is adequate ventilation.
• Do not horseplay.
• Keep floor and workspace neat, clean, and dry.
• Clean up spills immediately.
• If glassware breaks, do not clean it up; ask for teacher assistance.
• Tie back long hair.
• Never eat, drink, or smoke in the laboratory or workspace.
• Do not eat or drink any substances tested unless expressly
permitted to do so by a knowledgeable adult.
USING EQUIPMENT WITH CARE
• Set up apparatus far from the edge of the desk.
• Use knives or other sharp-pointed instruments with care.
• Pull plugs, not cords, when removing electrical plugs.
• Clean glassware before and after use.
• Check glassware for scratches, cracks, and sharp edges.
© Infobase PublishingSAFETY PRECAUTIONS 3
• Clean up broken glassware immediately.
• Do not use reflected sunlight to illuminate your microscope.
• Do not touch metal conductors.
• Use alcohol-filled thermometers, not mercury-filled thermometers.
USING CHEMICALS
• Never taste or inhale chemicals
• Label all bottles and apparatus containing chemicals
• Read labels carefully.
• Avoid chemical contact with skin and eyes (wear safety glasses, lab
apron, and gloves).
• Do not touch chemical solutions.
• Wash hands before and after using solutions.
• Wipe up spills thoroughly.
HEATING SUBSTANCES
• Wear safety glasses, apron, and gloves when boiling water.
• Keep your face away from test tubes and beakers.
• Use
glass.
test tubes, beakers, and other glassware made of Pyrex™
• Never leave apparatus unattended.
• Use safety tongs and heat-resistant gloves.
• IfBunsen
your laboratory does not have heat-proof workbenches, put your
burner on a heat-proof mat before lighting it.
• Take care when lighting your Bunsen burner; light it with the airhole
closed, and use a Bunsen burner lighter in preference to wooden
matches.
• Turn off hot plates, Bunsen burners, and gas when you are done.
• Keep flammable substances away from flames and other sources
of heat.
• Have a fire extinguisher on hand.
© Infobase PublishingSAFETY PRECAUTIONS 4
FINISHING UP
• Thoroughly clean your work area and any glassware used.
• Wash your hands.
• Be careful not to return chemicals or contaminated reagents to the
wrong containers.
• Do not dispose of materials in the sink unless instructed to do so.
• Clean up all residues and put them in proper containers for
disposal.
• Dispose
laws.
of all chemicals according to all local, state, and federal
BE SAFETY CONSCIOUS AT ALL TIMES!
© Infobase PublishingYou can also read
