Download File

Objective 4
1
Objective 4: Describe techniques for gathering information about celestial
bodies in the universe
This objective is further broken down into 3 outcomes
 Outcome 4A: Explain the operation of optical telescopes
 Outcome 4B: Explain the role of spectrometers (spectroscopes) in
determining characteristics of stars
 Outcome 4C: Explain the role of radio telescopes in determining
characteristics of stars and star systems and describe space probes
 Outcome 4A: Explain the operation of optical telescopes
Telescopes
Look up at a clear, cloudless night sky and you can
see a few thousand stars. With binoculars, you would
see thousands more. Use a telescope and millions of
stars will be revealed. Use one of the most powerful
telescopes available and billions of stars come into
view. Telescopes allow us to see fainter and more
distant objects in detail that cannot be detected by the
unaided eye. Two types of telescopes are described in
this section. Both provide us with a variety of
information about the objects that make up our
universe.
 Optical telescopes
Optical telescopes have been in use for the past 400 years. Think of optical telescopes as "light
collectors." That is what their series of lenses and mirrors do: gather and focus the light from stars so
that we can see it. The larger the area of the lenses or mirrors in a telescope, the greater the ability of the
telescope to see the faint light of objects that are very distant. Optical telescopes CANNOT be used
during the day, as the light in the atmosphere is brighter than the light from the stars. There are two
types of optical telescopes:
o Refracting telescopes: The first telescope ever designed was a simple refracting telescope.
Refracting telescopes use two lenses to
gather and focus starlight. The lens that
light goes through first is called the
primary (objective) lens. There is a limit
to how large the lens in a refracting
telescope can be. Any diameter over 1 m
causes the glass in the lens to warp under
its own weight. Trying to see through a
lens when that happens would be like
trying to make out details of the Moon by
looking through the bottom of a pop
bottle.
Objective 4
2
o Reflecting telescopes: Reflecting telescopes use mirrors instead of lenses to gather and focus
the light from stars. At one end of a reflecting telescope is a large concave mirror (called the primary, or
objective mirror), which is made from glass-like material that is coated with a thin layer of metal. The
metal, such as aluminum, is polished to a shiny finish so that it can reflect the faintest light it receives.
Mirrors can be made much larger than lenses, which is why reflecting telescopes can be made to see
farther into space than refracting telescopes. In addition, many mirrors can be put together to form one
huge primary (objective) mirror. The Canada-France-Hawaii observatory has a huge 3.6 meter mirror as
a primary mirror which is actually many smaller mirrors put together. The largest mirror used in a
reflecting telescope is over 12 meters large.
The Hubble space telescope
Although remote mountains make excellent sites for building and operating telescopes away from light
pollution and air pollution, astronomers are still at the mercy of the weather. Clouds, humidity (moisture
in the air), and even high winds can interfere with star-gazing. The development of the Hubble Space
Telescope offers a solution to these problems. Orbiting about 600 km above Earth, the Hubble Space
Telescope (which is a reflecting telescope) uses a series of mirrors to focus light from extremely distant
objects. Launched in 1990, the Hubble is cylinder-shaped, just over 13 m in length and 4.3 m in
diameter at its widest point. Each orbit that the Hubble makes around Earth takes about 95 min. Even
though the primary mirror of the Keck telescope in Hawaii is larger, Hubble can see farther and clearer
than Keck or any other Earth based telescope because the atmosphere doesn’t disturb the light reaching
Hubble in any way.
Objective 4
1. The basic function of optical telescopes is to act
as light - - collectors 2. Why can’t optical telescopes be used during the
day?
Light in atmosphere too bright
3. What happens as you increase the size of lenses
and/or mirrors in optical telescopes?
3
6. Why can reflecting telescopes be built to see farther into
space than refracting telescopes?
Mirrors can be made much larger than
lenses
7. Even a mirror has a limit to how large it can be. What
can be done to make the objective mirror of a reflecting
telescope larger than the maximum size limits of one single
mirror?
Put many mirrors together to form one
huge mirror
You can see further
4. Indicate what type of telescope is seen below and
label the two parts indicated.
8. What are 5 things that can interfere with images viewed
through an Earth based telescope?
Air pollution, light pollution, clouds
Humidity, wind
Use the following information to answer the next question
5. Indicate what type of telescope is seen below and
label the three parts that are pointed to. Then draw
how light from the star would travel through the
telescope
9. Which of the 4 telescopes above (A, B, C, or D) is
mostly likely to take the clearest image? EXPLAIN WHY
D-No atmosphere to distort images
-
10. What type of telescope is the Hubble space telescope?
Reflecting
-
Objective 4
4
 Outcome 4B: Explain the role of spectrometers (spectroscopes) in
determining characteristics of stars
Determining star composition
Now that astronomers could gaze deeper into the universe using simple telescopes, they faced a new
challenge — the stars. Galileo had seen the stars through his telescope, but what were they made of? The
spectroscope was one important technological advance that helped us learn more about the stars. Isaac
Newton passed a beam of light through a prism to produce a spectrum of colors. If you pass the light
through a narrow slit before sending it through a prism (which is found inside spectroscopes), the
resulting spectrum will contain all the colors.
The light from any light source can be split so the colors within that light source can be individually
seen (see diagram above or diagram below on the left). Joseph von Fraunhofer used a spectroscope to
observe the spectrum produced by the Sun, but he noticed dark lines in the spectrums of light throughout
the solar system, called spectral lines. He didn’t know what they meant but the answer was discovered
50 years later when two chemists used a spectroscope to observe various chemicals when they were
heated. The two scientists found that each particular element had its own unique spectral lines and
would absorb certain parts of the color spectrum if light were to pass through them (see the diagram
below on the right).
Objective 4
5
What the above information lead to is the fact that the composition of stars millions of light years
away could be determined (composition means what something is made of). The star emits light and the
light passes through the star’s own atmosphere, which is made up of various gases. Certain parts of the
light spectrum will be filtered out as the gases in that stars atmosphere filter out (absorb) those parts of
the spectrum.
Because we know which elements will filter out specific
parts of the spectrum, we can determine stars’ compositions
by analyzing the black-line fingerprints of the spectrum that
reaches us here on Earth. We know that hydrogen is the main
component of all stars with helium being the second main
component, so the spectrum from all stars will have the blackline fingerprints of hydrogen and helium. Other elements can
be found in some stars but not others, and their presence can
be determined by the presence of an element’s unique blackline fingerprints. The diagram to the right shows how to
determine a star’s composition based on the known black-line
fingerprints of known elements. You just have to match up
the black-line fingerprints of a star’s spectrum with the blackline fingerprints of known elements.
Objective 4
6
Determining star motion
Johann Doppler is famous for discovering what became known as the Doppler Effect. You hear it all
the time when an ambulance with its siren going drives past. The diagram to the right shows it well.
When a train blowing it’s whistle
while it is motionless (diagram 1 to
the right), a person behind it and a
person in front of it will hear the
same sound. But, if the train is
moving forward (diagram 2 to the
right) it compresses the sound
waves it emits in front of it and
stretches them out behind it. As a
result the person in front hears a higher pitched noise than the person behind.
Interestingly the same thing happens with light (which also travels in waves). You may remember
from grade 8 that each color has a different wavelength, with the
blue end having higher frequency waves, and the red end having
lower frequency waves (see diagram A to the right). When a light
emitting source, say a star, is moving away from us the light waves
are slightly lengthened and as a result the light looks redder. This is
called red shifting. When a star is moving toward Earth, the light
waves are slightly shortened and as a result the light looks bluer.
This is called blue shifting. Red shift and blue shift is measured by
observing the spectral lines of the light from stars. In diagram “B”,
star “x” is motionless when compared to Earth. Star “y” is moving
away from Earth, as the spectral lines are shifted towards the red
end. Star “z” is moving towards Earth, as the spectral lines are
shifted towards the blue end (a trick to remember this that the Earth
is blue, and stars moving towards Earth have spectral lines shifted
towards the blue end). One last note: The greater shift you see of
the spectral lines, the faster the star is moving either toward or
away from Earth.
Objective 4
11. What does a spectroscope do?
Separates light into all it’s colors
12. When light from a glowing substance passes
through a gas, what does that gas do to the light?
Absorb certain parts of the spectrum
7
17. The dot below shows a police car moving. Draw a
line in the direction the car is moving and draw a
person where he/she would be hearing a lower pitch
sound
Explain why a lower pitch sound
would be heard at this location
Sound waves lengthened
which we hear as a low
pitch
Use the following information to answer the next question
18. A shift towards the – RED - end of the spectrum
13. Think for yourselfWhat would cause the light in indicates a star or star system is moving away from
spectrum B to have more lines than the light in
Earth. A shift towards the – BLUE - end of the
spectrum A?
spectrum indicates a star or star system is moving
towards Earth.
The light from “B” passed through
more types of gases
Use the following information to answer the next question
14. Why are spectral lines present when we separate
the incoming light from stars into a spectrum
Gases present in the star’s atmosphere
absorb (filter out) certain parts
Use the following information to answer the next question
19. Is star C moving away or towards Earth? What
about B?
C: Toward
B: Away
Use the following information to answer the next
question
15. What gases are present in each of the stars?
Star 1
Star 2
Hydrogen, Helium, Calcium
All of them
16. What two black-line fingerprints will show up in
the spectrum of ALL stars.
The ones of hydrogen and helium
-
20. Above is the spectrum for the stars of Vega and
Sarir. Are they motionless, moving away, or moving
towards Earth? Which one is moving the fastest?
-Toward
-Sarir
21. By studying the spectrum of stars, scientists can
determine a stars
A. Mass and movement
B. Mass and distance from Earth
C. Composition and movement
D. Composition and distance from Earth
C
-
Objective 4

8
Outcome 4C: Explain the role of radio telescopes in determining
characteristics of stars and star systems and describe space probes
Radio telescopes
 What are radio telescopes and what are their advantages
Light isn’t the only kind of radiation coming from the stars. In the late nineteenth century, scientists found
out that light is just one form of electromagnetic
radiation. Other forms include radio waves,
infrared waves (heat), ultraviolet waves, X-ray
waves, and gamma ray waves. The diagram to the
right shows the entire spectrum of electromagnetic
radiation. Notice that light waves (which can be
seen with optical telescopes) occupy only a small
portion of the spectrum. But celestial objects such
as stars emit many other types of radiation,
including radio waves which we will focus on in
this outcome.
Studying radio waves emitted by objects in space gives astronomers data that are not available from the
visible spectrum. Radio waves are received from stars, galaxies, nebulae, black holes, and even some
planets—both in our own solar system and in others. These signals are mapped through the use of
sophisticated electronics and computers.
With the development of radio telescopes, astronomers gained several advantages over optical
telescopes. Radio waves are not affected by weather and can be detected during the day and at night. They
are also not distorted by clouds, pollution, or the atmosphere as are light waves. Furthermore, by focusing
their radio telescopes on certain areas of space that appear empty, astronomers have discovered additional
information about the composition and distribution of matter in space—information that cannot be detected
by optical equipment. For example, although hydrogen outside of stars emits no light, it does emit energy at
a specific wavelength in the electromagnetic spectrum. Using radio telescopes, astronomers have been able
to map the distribution of hydrogen in the Milky Way galaxy. This is how they learned that the shape of our
galaxy is a spiral.
Radio waves have wavelengths that are millions of times longer than light waves, meaning that these
waves give less resolution, but can penetrate dust clouds in the galaxy, where light waves cannot. They
can also go right through clouds not to mention materials like wood,
brick and cement (this is why you can get radio reception almost
anywhere). Radio waves can also be picked up during the day so
scientists can work at any time (optical telescopes can only be used at
night.) Having such large waves requires a large object to read these
waves. To the right is a radio telescope found in Arecibo, Puerto Rico
that has a diameter of more than 300 meters. Radio telescopes are
typically made of metal mesh and resemble a satellite dish.
 What do radio telescopes detect?
Radio telescopes cannot “see” radio waves or anything else. Radio waves are not in the visible light
spectrum so there is nothing to see. In the early days of professional radio astronomy the movement of
dials and needles monitored the incoming radio waves. The needle is similar to the kind you see in a
voltmeter or even the speedometer of a car. The needles would jump around as strong radio waves were
picked up. Astronomers then graphed the data. Today, computers can provide an
artificial image which uses color codes for the strength of radio waves. The
image to the right shows radio waves being picked up from a galaxy. Black
means no radio waves are picked up, but as the shades/colors get lighter, this
represents an increase of radio wave emission from objects within the galaxy.
Objective 4
9
Space probes
Telescopes, optical or radio, cannot provide answers to all the questions we have about our solar
system. Often it is necessary to send the observation equipment right to the object so that tests not
possible to conduct by telescope can be done. In the past several decades, astronomers have done just
that, sending numerous space probes to explore distant areas of our planetary neighborhood. Space
probes are unmanned devices which go to planets (other than Earth) or other celestial objects (comets,
asteroids, ect…) to make observations of them.
When a device takes observations of Earth we call the device a satellite (more specifically a remote
sensing satellite), not a probe. When a device takes observations of other planets, asteroids or other
celestial bodies we call the device a space probe. Some probes fly by celestial bodies and take pictures,
some will be put in an orbit of celestial bodies and become a satellite for them, while others actually
land on celestial bodies and make observations such as analyzing the soil. All probes are unmanned. A
probe was sent to Mars in
2004 that sent back many
images of the Mars
landscape including
pictures which show that
water once flowed on Mars.
22. Why do you think that some scientists say that
optical telescopes give them a very limited amount of
information about space?
Visible light is such a small part of
the electromagnetic spectrum
26. Besides picking up radio waves and not being
affected by atmospheric conditions, what is another
advantage of using radio telescopes over optical
telescopes?
Can be used during the day
27. Why must radio telescopes be so much larger than
23. Circle the part of the electromagnetic spectrum
that radio telescopes will be able to detect. Draw a box optical telescopes?
Radio waves millions of times as large
around the part that can be detected with optical
telescopes (refracting or reflecting telescopes)
as light waves
28. If radio waves can’t be seen, how do scientists
know the strength of radio waves coming from
various objects in space?
24. What kinds of objects emit radio waves?
Stars, galaxies, nebulae, black holes
Computers provide artificial image
using color codes
29. Explain what a space probe is
25. Optical telescopes are built in specific areas on the
Unmanned objects sent to celestial
Earth. Good areas have lots of clear weather and low
objects to make observations of them
pollution. This is because clouds, rain, snow, pollution,
30. Which of the following do space probes NOT do?
dust and various other things can easily block light.
A. Fly by celestial bodies and take pictures
Therefore, areas like Great Britain which get a lot of
B. Send astronauts to celestial objects for
rain is not an optimal place for optical telescopes.
observation
However, radio telescopes are found in many areas of
C. Take pictures of Earth
Earth including Great Britain. Why can radio
D. Orbit celestial bodies such as planets or
telescopes be put almost anywhere?
asteroids.
Radio waves not affected by
E. Land on foreign celestial bodies
F. There are 2 things above that space probes do
atmospheric conditions like light waves
not do
are
F
Objective 4
-
10
Objective 4
11
Activity book created by Devon Rossington
Vincent Massey School