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다양한 창문을 통한 우주
2017-05-05
1
내용
왜 다양한 창문?
 대기의 영향
 망원경의 성능
 관측에서 얻는 정보
 중요 망원경들
 차세대 망원경들

2017-05-05
2
망원경의 성능
집광력 : 구경 제곱에 비례
분해능 : 구경에 비례
파장에 반비례
 지구 대기에 의한 분해능의 저하 : 시상효과
 광학 우주 망원경이 필요한 이유
배율 : 대물렌즈 부착 (확대)
 검출기
(눈, 사진, CCD) : 상(image)

; 밝기, 위치,
 분광기+검출기 : 스펙트럼 :

별의 구성물질에 대한 정보,
2017-05-05
3
Interferometry
One of the reasons astronomers build
big telescopes is to increase resolving
power.
 Astronomers have been able to achieve
very high resolution by connecting
multiple telescopes together to work as
if they were a single telescope.

 This
method of synthesizing a larger
telescope is known as interferometry.
Interferometry
To work as an interferometer, the
separate small telescopes must combine
their light through a network of mirrors.
 Also, the path that each light beam
travels must be controlled so
that it does not vary by
more than some small
fraction of the
wavelength.

Interferometry
 Turbulence
in Earth’s atmosphere
constantly distorts the light.

High-speed computers must continuously
adjust the light paths as Earth rotates.
Interferometry
As the wavelength of light is very
short—roughly 0.0005 mm—building
optical interferometers is one of the
most difficult technical problems that
astronomers face.
 Infrared- and radio-wavelength
interferometers are slightly easier to
build, because the wavelengths are
longer.

Interferometry
A number of modern telescopes can
work as interferometers.
 The VLT consists of four 8.2-m
telescopes that can operate separately.



These can be linked together through underground
tunnels with three 1.8-m telescopes on the same
mountaintop.
The resulting optical
interferometer provides
the resolution of a
telescope 200 meters
in diameter.
Interferometry
The two Keck 10-m telescopes can be
used as an interferometer.
 The CHARA array on Mt. Wilson
combines six 1-meter telescopes
to create the equivalent of
a telescope one-fifth of
a mile in diameter.
 The Large Binocular
telescope can be used
as an interferometer.

Interferometry
 Although
turbulence in Earth’s
atmosphere can be partially averaged
out in an interferometer, plans are
being made to put interferometers in
space.

For example, the Space Interferometry Mission will
work at optical wavelengths and study everything
from the cores of erupting galaxies to planets
orbiting nearby stars.
Building Scientific Arguments

Why do astronomers build observatories
at the tops of mountains?

To create this argument, you need to think about
the powers of a telescope.
Building Scientific Arguments
 Astronomers
have joked that the
hardest part of building a new
observatory is constructing the road to
the top of the mountain.
It certainly isn’t easy to build a large, delicate
telescope at the top of a high mountain.
 However, it is worth the effort.

Building Scientific Arguments
A
telescope on top of a high mountain
is above the thickest part of Earth’s
atmosphere.
There is less air to dim the light.
 There is less water vapor to absorb infrared
radiation.
 Even more important, the thin air on a
mountaintop causes less disturbance to the
image.
 Consequently, the seeing is better.

Building Scientific Arguments
A
large telescope on Earth’s surface
has a resolving power much better
than the distortion caused by
Earth’s atmosphere.

So, it is limited by seeing—not by its own
diffraction.
Building Scientific Arguments
 Astronomers
not only build telescopes
on mountaintops, they also build
gigantic telescopes many meters in
diameter.
 Revise your argument to focus on
telescope design.

What are the problems and advantages in
building such giant telescopes?
Special Instruments
 Just
looking through a telescope
doesn’t inform you of much.
 To use an astronomical telescope to
learn about stars, you must be able
to analyze the light the telescope
gathers.

Special instruments attached to the telescope
make that possible.
Imaging Systems
 The
original imaging device in
astronomy was the photographic
plate.
It could record faint objects in long time
exposures and could be stored for later analysis.
 However, photographic plates have been almost
entirely replaced in astronomy by electronic
imaging systems.

Imaging Systems
 Most
modern astronomers use
charge-coupled devices (CCDs) to
record images.
A CCD is a specialized computer chip
containing roughly a million microscopic light
detectors arranged in an array about the size of
a postage stamp.
 These devices can be used like a small
photographic plate.

Imaging Systems
 CCDs
have dramatic advantages.
They can detect both bright and faint objects
in a single exposure.
 They are much more sensitive than a
photographic plate.
 They can be read directly into computer
memory for later analysis.

Imaging Systems
 Although
CCDs for astronomy are
extremely sensitive and therefore
expensive, less sophisticated CCDs
are used in video cameras and
digital cameras.
Imaging Systems
The image from a CCD is stored as
numbers in computer memory.
 So, it is easy to manipulate the image to
bring out details that would not
otherwise be visible.



For example, astronomical images are often
reproduced as
negatives—with the sky
white and the stars dark.
This makes the faint
parts of the image
easier to see.
Imaging Systems
 Astronomers
also manipulate images to
produce false-color images.

In these, the colors represent different levels of
intensity and are not related to the true colors of the
object.
Imaging Systems
In the past, measurements of intensity
and color were made using a
photometer—a highly sensitive light
meter attached to a telescope.
 Today, most such measurements are
made on CCD images.


As the CCD image is easily digitized, brightness
and color can be measured to high precision.
The Spectrograph
To analyze light in detail, you need to
spread the light according to wavelength
into a spectrum—a task performed by a
spectrograph.
 You can understand how this works if
you reproduce an experiment performed
by Isaac Newton in 1666.

The Spectrograph

Boring a hole in his window shutter,
Newton admitted a thin beam of sunlight
into his darkened bedroom.


When he placed a prism in the beam, the sunlight
spread into a beautiful spectrum on the far wall.
From this, he concluded that white light was made of
a mixture of all the colors.
The Spectrograph
Newton didn’t think in terms of
wavelength.
 However, you can use this modern
concept to see that the light passing
through the prism is bent at an angle
that depends on the wavelength.



Violet (shortest wavelength)
bends most and red
(longest wavelength) least.
Thus, the white light that
enters the prism is spread
into a spectrum.
The Spectrograph
A
typical prism spectrograph contains
more than one prism, to spread the
light farther, and lenses, to guide the
light into the prism and to focus the
light into the camera.

However, nearly all modern spectrographs use
a grating in place of a prism.
The Spectrograph
A
grating is a piece of glass with
thousands of microscopic parallel
lines scribed onto its surface.
Different wavelengths of light reflect from the
grating at slightly different angles.
 So, white light is spread into a spectrum and
can be recorded, often by a CCD camera.

The Spectrograph
 You
can see this effect if you tilt a
CD or DVD in bright light.

The colors that flash across its surface are
produced as different wavelengths of light are
reflected at different angles from the closely
spaced grooves.
The Spectrograph
 Recording
the spectrum of a faint
star or galaxy can require a long
time exposure.

So, astronomers have developed multiobject
spectrographs that can record the spectra of
as many as 100 objects simultaneously.
The Spectrograph
Fiber optic strands collect the light from
many objects in the field of view and
pipe the light to a single spectrograph.
 In some cases, a robotic arm can rapidly
place the fibers in the right place—to
collect light from many galaxies in the
telescope’s field of view.


Such multiobject spectrographs automated by
computers have made possible large surveys of
many thousands of stars or galaxies.
The Spectrograph
 The
spectrum of an astronomical
object can contain hundreds of
spectral lines produced by the
atoms in the object.

As astronomers must measure the wavelength
of the lines in a spectrum, they use a
comparison spectrum as a calibration of their
spectrograph.
The Spectrograph
 Special
bulbs built into the
spectrograph produce bright lines
given off by such atoms as thorium
and argon or neon.


The wavelengths of these spectral lines have been
measured to high precision in the laboratory.
So, astronomers can use spectra of these light
sources like roadmaps to measure wavelengths
and identify spectral lines in the spectrum of a
star, galaxy, or planet.
The Spectrograph
 As
astronomers understand how light
interacts with matter, a spectrum
carries a tremendous amount of
information.
That makes a spectrograph the astronomer’s
most powerful instrument.
 An astronomer recently remarked, “We don’t
know anything about an object till we get a
spectrum.”

Building Scientific Arguments
 What
is the difference between light
going through a lens and light
passing through a prism?




When you think about natural processes, it is often
helpful to compare similar things.
Scientific arguments often make such
comparisons.
A few simple rules explain most natural events.
So, the similarities are often revealing.
Building Scientific Arguments
 What
is the difference between light
going through a lens and light
passing through a prism?




When you think about natural processes, it is often
helpful to compare similar things.
Scientific arguments often make such
comparisons.
A few simple rules explain most natural events.
So, the similarities are often revealing.
Building Scientific Arguments

A refracting telescope producing
chromatic aberration and a prism
dispersing light into a spectrum are two
examples of the same phenomenon.

However, one is bad and one is good.
Building Scientific Arguments

When light passes through the curved
surfaces of a lens, different wavelengths
are bent by slightly different amounts—
and the different colors of light come to
focus at different focal lengths.

This produces the color fringes in an image called
chromatic aberration—and that’s bad.
Building Scientific Arguments

However, the surfaces of a prism are
made to be precisely flat.



All the light enters the prism at the same angle,
and any given wavelength is bent by the same
amount.
Thus, white light is dispersed into a spectrum.
You could call the dispersion of light by a prism
‘controlled chromatic
aberration’—and that’s
good.
Building Scientific Arguments
 Now,
you can build your own
argument comparing similar things.
CCDs have been very good for astronomy, and
they have almost completely replaced
photographic plates.
 How are CCD chips similar to photographic
plates?
 How are they better?

Radio Telescopes
A
radio telescope is a device that
measures the strength of radio
waves coming from a small spot
on the sky at a specific
wavelength.
Radio Telescopes

Many objects in the universe emit radio
waves.


Thus, radio observations can reveal a great deal
about some celestial bodies.
Earth’s atmosphere is transparent to a
wide range of radio wavelengths in what
is called the radio window.

So, radio astronomers
can study the sky
from Earth’s surface.
Operation of a Radio Telescope

A radio telescope usually consists of
four parts—a dish reflector, an antenna,
an amplifier, and a recorder.

The components, working together, make it
possible for astronomers to detect radio radiation
from celestial objects.
Operation of a Radio Telescope

The dish reflector of a radio telescope,
like the mirror of a reflecting telescope,
collects and focuses radiation.
As radio waves are much longer than light waves,
the dish need not be as smooth as a mirror.
 In some radio telescopes, the reflector may not
even be dish-shaped, or
the telescope may
contain no reflector at all.

Operation of a Radio Telescope
 Whereas
the dish may be many meters
in diameter, the antenna may be as
small as your hand.

Like the antenna on a TV set, its only function is to
absorb the radio energy and direct it along a cable
to an amplifier.
Operation of a Radio Telescope
 After
amplification, the signal goes
to some kind of recording
instrument.

Most radio observatories record data into
computer memory.
Operation of a Radio Telescope
 Humans
can’t see radio
waves.
 So,
astronomers must convert them into
something perceptible.
Operation of a Radio Telescope
 One
way is to measure the strength of
the radio signal at various places in
the sky and draw a map in which
contours mark areas of uniform radio
intensity.
Operation of a Radio Telescope
 You
might compare such a map to a
seating diagram for a baseball
stadium in which the contours mark
areas in which the seats have the
same price.
Operation of a Radio Telescope
 Contour
maps are very common
in radio astronomy and are often
reproduced using false colors.
Limitations of the Radio Telescope
A
radio astronomer works under
three handicaps:
 Poor
resolution
 Low intensity
 Interference
Limitations of the Radio Telescope
 You
have learned that the resolving
power of an optical telescope
depends on the diameter of the
objective lens or mirror.
 It also depends on the wavelength
of the radiation.
Limitations of the Radio Telescope

At very long wavelengths—like those of
radio waves—the diffraction fringes
become very large.
 That

makes the images fuzzy.
As with an optical telescope, the larger
the telescope, the smaller the fringes
and the better the resolution.
 Thus,
radio telescopes must be quite large.
Limitations of the Radio Telescope
 Even
so, the resolving power of a
radio telescope is not good.
A dish 30 m in diameter receiving radiation
with a wavelength of 21 cm has a resolving
power of about 0.5°.
 Such a radio telescope would be unable to
show you any details in the sky smaller than
the moon.

Limitations of the Radio Telescope

Fortunately, radio astronomers can
combine two or more radio telescopes to
form a radio interferometer capable of
much higher resolution.


The Very Large Array (VLA) consists of 27 dish
antennas spread in a Y-shape across the New
Mexico desert.
In combination,
the antennas have
the resolving power of
a radio telescope 36 km
(22 mi) in diameter.
Limitations of the Radio Telescope
 The
VLA can resolve details smaller
than 1 second of arc.

Eight new dish antennas being added across
New Mexico will give the VLA 10 times better
resolving power.
Limitations of the Radio Telescope
 Another
large radio interferometer—the
Very Long Baseline Array (VLBA)—
consists of matched radio dishes
spread from Hawaii to the Virgin
Islands.
 It has an effective diameter almost as
large as Earth.
Limitations of the Radio Telescope
 The
second handicap radio
astronomers face is the low intensity
of the radio signals.
You have learned that the energy of a photon
depends on its wavelength.
 Photons of radio energy have such long
wavelengths that their individual energies are quite
low.
 To get strong signals focused on the antenna, the
radio astronomer must build large collecting
dishes.

Limitations of the Radio Telescope

The largest fully steerable radio telescope
in the world is at the National Radio
Astronomy Observatory in Green Bank,
West Virginia.


The telescope has a reflecting surface 100 m in
diameter—big enough to hold an entire football
field—and can be pointed anywhere in the sky.
Its surface consists of 2004
computer-controlled panels
that adjust to maintain
the shape of the reflecting
surface.
Limitations of the Radio Telescope
 The
largest radio dish in the world
is 300 m (1,000 ft) in diameter.
So large a dish can’t be supported in the usual
way.
 Thus, it is built into a mountain valley in
Arecibo, Puerto Rico.

Limitations of the Radio Telescope
The reflecting dish is a thin metallic
surface supported above the valley floor
by cables attached near the rim.
 The antenna hangs
above the dish on
cables from three
towers built on three
mountain peaks that
surround the valley.

Limitations of the Radio Telescope

This telescope is not fully steerable.
 It

can look only overhead.
However, the operators can change its
aim slightly by moving
the antenna above
the dish and waiting
for Earth’s rotation
to point the telescope
in the proper direction.
Limitations of the Radio Telescope

This telescope is not fully steerable.
 It

can look only overhead.
However, the operators can change its
aim slightly by moving
the antenna above
the dish and waiting
for Earth’s rotation
to point the telescope
in the proper direction.
Limitations of the Radio Telescope
 The
third handicap a radio
astronomer faces is interference.



A radio telescope is an extremely sensitive radio
receiver listening to radio signals thousands of
times weaker than artificial radio and TV
transmissions.
Such weak signals are easily drowned out by
interference.
Sources of such interference include everything
from poorly designed transmitters in Earth
satellites to automobiles with faulty ignition
systems.
Limitations of the Radio Telescope
 To
avoid this kind of interference,
radio astronomers locate their
telescopes as far from civilization as
possible.

Hidden deep in mountain valleys, they are able to
listen to the sky—protected from human-made
radio noise.
Limitations of the Radio Telescope
 To
avoid this kind of interference,
radio astronomers locate their
telescopes as far from civilization as
possible.

Hidden deep in mountain valleys, they are able to
listen to the sky—protected from human-made
radio noise.
Advantages of Radio Telescopes
 Building
large radio telescopes
in isolated locations is
expensive.
 However, three factors make it
all worthwhile.
Advantages of Radio Telescopes
 First,
and most important, a radio
telescope can show where clouds
of cool hydrogen are located
between the stars.


As 90 percent of the atoms in the universe are
hydrogen, that is important information.
Large clouds of cool hydrogen are completely
invisible to normal telescopes—because they
produce no visible light of their own and reflect too
little to be detected on photographs.
Advantages of Radio Telescopes
 However,
cool hydrogen emits a radio
signal at the specific wavelength of
21 cm.
The only way to detect these clouds of gas is
with a radio telescope that receives 21-cm
radiation.
 These hydrogen clouds are the places where
stars are born.

Advantages of Radio Telescopes
 There
is a second reason why large
radio telescopes are worthwhile.

As radio signals have relatively long
wavelengths, they can penetrate the vast
clouds of dust that obscure the view at visual
wavelengths.
Advantages of Radio Telescopes

Light waves are short, and they interact
with tiny dust grains floating in space.
 Thus,
the light is scattered and never
penetrates the dust to reach optical
telescopes on Earth.

However, radio signals from far across
the galaxy pass unhindered through the
dust—giving radio astronomers an
unobscured view.
Advantages of Radio Telescopes
 Finally,
a radio telescope can help
astronomers understand the complex
processes that go on in clouds of gas
in space.



It can detect radio emission from many different
molecules that form naturally in these clouds.
Furthermore, certain high-energy processes—such
as hot gas trapped in magnetic fields—emit
characteristic radio signals.
Radio telescopes can help astronomers understand
such violent processes as exploding stars and
erupting galaxies.
Building Scientific Arguments

Why do optical astronomers build big
telescopes, whereas radio astronomers
build groups of widely separated smaller
telescopes?

Once again, you can learn a lot by building a
scientific argument based on comparison.
Building Scientific Arguments
Optical astronomers try to maximize
light-gathering power.
 Radio astronomers, in contrast, try to
maximize resolving power.


As radio waves are so much
longer than light waves,
a single radio telescope
can’t see details in the sky
much smaller than the moon.
Building Scientific Arguments

By linking radio telescopes miles apart,
radio astronomers build a radio
interferometer that can simulate a radio
telescope miles in diameter and thus
increase the resolving power.
Building Scientific Arguments
The difference between the wavelengths
of light and radio waves makes a big
difference in building the best telescopes.
 Keep that difference in mind as you build
a new argument.


Why don’t radio astronomers want to build their
telescopes on mountaintops as optical astronomers
do?
Astronomy from Space

You have learned about the observations
that ground-based telescopes can make
through the two atmospheric windows in
the visible and radio parts of the
electromagnetic spectrum.
Astronomy from Space

You have learned about the observations
that ground-based telescopes can make
through the two atmospheric windows in
the visible and radio parts of the
electromagnetic spectrum.
Astronomy from Space

Most of the rest of the electromagnetic
radiation—infrared, ultraviolet, X ray, and
gamma ray—never reaches Earth’s
surface.

To observe at these wavelengths, telescopes must
fly above the atmosphere in high-flying aircraft,
rockets, balloons, and satellites.
Astronomy from Space
 Before
you blast off, you should
check out the extreme limits of
astronomy from Earth’s surface.

Some observations can be made in the nearinfrared and the near-ultraviolet.
The Ends of the Visual Spectrum

Astronomers can observe in the nearinfrared just beyond the red end of the
visible spectrum.

Some of this infrared radiation leaks through the
atmosphere in narrow, partially open atmospheric
windows scattered from 1,200 nm to about 40,000
nm.
The Ends of the Visual Spectrum
 Infrared
astronomers usually measure
wavelength in micrometers (10-6
meters).
 So, they refer to this wavelength range
as 1.2 to 40 micrometers or microns.


In this range, much of the radiation is absorbed by
water vapor, carbon dioxide, and oxygen molecules
in Earth’s atmosphere.
Thus, it is an advantage to place telescopes on
mountains—where the air is thin and dry.
The Ends of the Visual Spectrum

For example, a number of important
infrared telescopes observe from the
4,150-m (13,600-ft) summit of Mauna
Kea in Hawaii.

At this altitude, they are
above much of the water
vapor—which is the main
absorber of infrared.
The Ends of the Visual Spectrum

The far-infrared range—which includes
wavelengths longer than 40
micrometers—can reveal the secrets of
planets, comets, forming stars, and other
cool objects.

However, these wavelengths are absorbed high in
the atmosphere.
The Ends of the Visual Spectrum
 To
observe in the far-infrared,
telescopes must venture to high
altitudes.

Remotely operated infrared telescopes
suspended under balloons have reached
altitudes as high as 41 km (25 mi).
The Ends of the Visual Spectrum
 For
many years, a NASA jet transport
carried a 91-cm infrared telescope
and a crew of astronomers to
altitudes of 12,000 m (40,000 ft)—to
get above 99 percent of the water
vapor in Earth’s atmosphere.
The Ends of the Visual Spectrum

Now retired from service, that airborne
observatory will soon be replaced with the
Stratospheric Observatory for Infrared
Astronomy (SOFIA)—a Boeing 747 that
will carry a 2.5-m telescope to the fringes
of the atmosphere.
The Ends of the Visual Spectrum
 If
a telescope observes in the
near-infrared, the detector on
which the radiation falls must be
cooled.
Infrared radiation is absorbed as heat.
 If the detector is warm, it is impossible to tell
the difference between the infrared radiation
and the heat in the detector.

The Ends of the Visual Spectrum
 Such
detectors are usually
cooled with liquid nitrogen.
The Ends of the Visual Spectrum
 If
a telescope observes at farinfrared wavelengths, then the entire
telescope must be cooled.

An astronomer observing a bright star at 10
micrometers with an uncooled telescope on a
high mountaintop described it as “like trying to
observe a star in the daytime with a telescope
that is on fire.”
The Ends of the Visual Spectrum
 At
the short-wavelength end of the
spectrum, astronomers can observe
in the near ultraviolet.


Your eyes do not detect this radiation.
However, it can be recorded by photographic
plates and CCDs.
The Ends of the Visual Spectrum
 Wavelengths
shorter than about 290
nm, the far-ultraviolet, are completely
absorbed by the ozone layer
extending from 20 km to about 40 km
above Earth’s surface.
The Ends of the Visual Spectrum
 No
mountain is that high, and no
balloon or airplane can fly that high.
 So,
astronomers cannot observe in the farultraviolet—without going into space.
Telescopes in Space

To observe far beyond the ends of the
visible spectrum, astronomical
telescopes must go above Earth’s
atmosphere into space.
Telescopes in Space
 This
is very expensive and difficult.
 However, it is the only way to study
some processes.
Stars are born inside clouds of gas and dust—and
visible wavelengths cannot escape from these dust
clouds.
 Only observations in the infrared can reveal the
secrets of star formation.
 Black holes are small and hard to detect.
 However, matter flowing into a black hole emits X
rays.

Telescopes in Space
Many space telescopes are small
satellites designed to make specific
observations for a short period.
 Some, though, are large general
purpose telescopes.

Telescopes in Space

Decades ago, astronomers developed a
plan to place a series of great
observatories in space.

Those space telescopes have revolutionized
human understanding of what you are and where
you are in the universe.
Telescopes in Space
There are three points to note about
these great observatories in space.
 First, not only can a telescope in space
observe at a wide range of
wavelengths, but it is above the
atmospheric blurring called seeing.


The Hubble Space Telescope observes mostly at
visual wavelengths and has the advantage of
sharp images undistorted by seeing.
Telescopes in Space
 Second,
these telescopes must be
specialized for their wavelength range.



The Compton Gamma Ray Observatory had special
detectors.
The Chandra X Ray Observatory must have
cylindrical mirrors,
The Spitzer Infrared
Observatory must have
cooled optics.
Telescopes in Space
Finally, the Hubble Space Telescope
has been maintained by visits from
astronauts.
 Such visits are expensive, though—and
the future of Hubble is in doubt.

Telescopes in Space
Astronauts cannot
reach the Chandra
and Spitzer
telescopes.
 The Compton
Observatory was
removed from orbit
in 2000.

Telescopes in Space
 Space
observatories have limited
lifetimes.
 Astronomers are already planning
the next great observatory in space.

The new James Webb Space Telescope,
though, will not be available for many years.
Telescopes in Space
Many people think that the Hubble
Space Telescope and other space
telescopes are put in space to get
closer to the objects they study.
 That is a common misconception.


Of course, you could explain that space
telescopes go into orbit to get above Earth’s
atmosphere and avoid seeing distortions and the
absorption of wavelengths outside the two
atmospheric windows.
Telescopes in Space
 These
great observatories in space
are controlled from research centers
on Earth and are open to proposals
from any astronomer with a good
idea.
Competition is fierce, though.
 Only the most worthy projects win approval.

Building Scientific Arguments

Why can infrared astronomers observe
from high mountaintops, whereas X-ray
astronomers must observe from space?

Once again, you can analyze this question by
building a scientific argument based on
comparison.
Building Scientific Arguments
 Infrared
radiation is absorbed by
water vapor in Earth’s atmosphere.


If you built an infrared telescope on top of a high
mountain, you would be above most of the water
vapor in the atmosphere.
Thus, you could collect some infrared radiation
from the stars.
Building Scientific Arguments
 However,
the longer-wavelength
infrared radiation is absorbed much
higher in the atmosphere.

You couldn’t observe it from the mountaintop.
X
rays are absorbed in the uppermost
layers of the atmosphere.

You would not be able to find any mountain high
enough to get an X-ray telescope above those
absorbing layers.
Building Scientific Arguments
 To
observe the stars at X-ray
wavelengths, you would need to put
your telescope in space, above Earth’s
atmosphere.
Building Scientific Arguments
 Now,

build another argument.
Why must the Hubble Space Telescope be in
space when it observes in the visual wavelength
range?
관측에서 얻는 정보 :빛-분광







천체의 위치 : 측성
천체의 밝기 : 측광
천체의 운동 : 스펙트럼 = 분광 관측
천체의 구성 원소 : 스펙트럼 = 분광관측
고온의 밀집된 기체 덩어리 또는 액체 고체
– 흑체복사
 온도가 높을수록 파란색의 빛을 많이 냄.
모든 원자는 고유의 주파수를 가지고 있다. 일종의 지문 같은 것
 빛을 주파수 또는 파장별로 분석을 하면 천체에 있는 원소가 무엇인지를
알 수 있다.
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먼 곳의 천체의 운동은 어떻게
아나? -> 도플러 효과 이용

소리에서의 음, 빛에서의 색
-> 사람이 진동수를 감지하는 방법
단위시간당 진동수가 크면 고음, 파란색
 진동수를 증가시키는 방법

 테이프를
빨리 돌린다.
 서로 접근한다.
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차세대 지상 광학 망원경
GMT : 7 * 8 m
 (24.8 m ;2018)

TMT : 492 segments
 (30m : 2018)

E-ELT : 5 mirrors
 (42 m : 2020)

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