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Science 30

Unit C – Electromagnetic Energy

Outcome 2: Students will describe the properties of the electromagnetic spectrum and

their applications in medical technologies, communication systems and remote-sensing

technologies used to study the universe.

Specific Outcome 2.7: Explain, in general terms, the design of telescopes that

are used to gather information about the universe through the collection of as

much EMR as possible; i.e. reflecting and refracting optical and radio

telescopes.

Specific Outcome 2.9: Describe, in general terms, how a spectroscope

can be used to determine the composition of incandescent objects or

substances, and the conditions necessary to produce emission (bright

line) and absorption (dark line) spectra, in terms of light source and

temperature.

Specific Outcome 2.10: Describe technologies used to study stars

o Spectroscopes used to analyze the distribution of energy in a star’s

continuous emission spectrum can be used to estimate the surface

temperature of the star

o Doppler-shift technology used to measure the speed of distant stars

provides evidence that the universe is expanding

Specific Outcome 2.11: Describe, in general terms, the evolution of stars and the

existence of black holes, white dwarves and neutron stars.

Textbook reference pages: p. 441 – 454 in Science 30

Most of what we know about our universe comes from studying electromagnetic waves

(EMR) from space.

Using telescopes, astronomers can detect distant stars, planets and galaxies.

o The nearest galaxy to our own is 2.9 million light years away. That means

we are seeing it as it was 2.9 million years ago!

TELESCOPES

REFRACTING TELESCOPES

Refracting telescopes consist of 2 lenses to focus the light.

This type of telescope has it drawbacks due to its use of lenses.

o The lenses need to be made of high quality glass.

o The size of the lenses needed to be relatively small due to mass of the

lenses.

2007 Alberta Education

Name: _______________________________

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https://commons.wikimedia.org/w/index.php?curid=34810016

https://commons.wikimedia.org/w/index.php?curid=138997

REFLECTING TELESCOPES

Reflecting telescopes have two mirrors to focus the light and reflect the light from

the stars.

Reflecting telescopes have a few advantages over refracting telescopes

o Mirrors do not break light into its component colours

o Reflecting telescopes can gather infrared and ultraviolet light as well

o The telescopes can have very large openings since the light reflects off

the mirror

o Curved mirrors can be larger than glass lenses as they can support their

weight better than a large lens.

Modern reflecting telescopes use much larger mirrors to collect and reflect more

light.

o The Canada-France-Hawaii telescope (CFHT) uses a mirror that is 3.6 m in

diameter.

o The Giant Magellan Telescope is under construction in the Atacama

Desert, Chile and will be completed in 2025. It will consist of seven 8.4 m

diameter mirrors creating a reflecting telescope with a collecting area

equivalent to a 22 metre diameter mirror.

RADIO TELESCOPES

Radio waves have the longest wavelengths of the

EMR so a very large dish is required to collect this

radiation

The radio waves are collected and transformed into

an electrical signal for interpretation of composition

and distribution of interstellar matter

Radio observatories are often set up in valleys to

shield them from other electromagnetic interference

A 305 m dish located in Puerto Rico is the world’s

largest full dish radio telescope fixed in the ground.

To improve resolution of the long radio waves, radio

telescopes are grouped into arrays – long lines of

radio telescopes.

The Very Large Array in New Mexico has twenty-seven

25-m radio telescopes arranged in a Y-shape that

would represent a telescope with a diameter of 27 km.

2007 Alberta Education

Name: _______________________________

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SPACE TELESCOPES

Reflecting and refracting telescopes on Earth are affected by the atmosphere

and weather.

The Hubble Space Telescope gathers, infrared, ultraviolet and visible light without

the interference of air and light pollution on Earth.

Most of radiation from interstellar matter, planets, comets and asteroids are in the

infrared region of the EMS.

Three galaxies colliding seen by Hubble, about 400 million light-years away (~4

1021 km).

The Chandra X-ray telescope is a space-based telescope used to gather X-ray

radiation.

o X-rays are at the high energy end of the EMS and behaves more like a

particle than a wave

o The telescope was designed to detect X-ray radiation from exploded

stars, galaxy clusters and matter around black holes – very hot regions of

the Universe

http://news.softpedia.com/news/Hubble-Images-Colliding-Galaxies-108620.shtml

2007 Alberta Education

Interesting Facts about Chandra Taken from http://chandra.harvard.edu/about/top_ten.html

Chandra’s resolving power is equivalent to

the ability to read a stop sign at a distance

of 19 kilometres.

The light from some of the quasars

observed by Chandra will have been

traveling through space for ten billion

years.

Chandra can observe X-rays from particles

up to the last second before they fall into

a black hole.

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ANALYZING STARLIGHT

By studying the Universe across the spectrum we can get a more complete

understanding of objects in space.

The light from each part of the electromagnetic spectrum brings us valuable and

unique information.

o X-Rays bring us information about high energy phenomena such as black

holes, supernova remnants, hot gas, and neutron stars.

o Ultraviolet radiation reveals hot stars and quasars while visible light shows

us warmer stars, planets, nebulae, and galaxies.

o In the infrared spectrum we see cool stars, regions of star birth, cool dusty

regions of space, and the core of our galaxy.

o Radiation in the radio wave frequency shows us cold molecular clouds

and the radiation left over from the Big Bang.

X-ray image

showing hot

gas near the

center of our

Milky Way

Galaxy (CXO).

Ultraviolet view

of hot white

dwarf stars in a

nearby galaxy

(ASTRO-1).

Visible light

image showing

stars of different

colors.

Infrared view of

glowing dust near

the center of our

Galaxy (2MASS).

Radio image of a

supernova

remnant (NRAO).

We have the technology to be able to tell what stars are made of, if they are

moving or not and in what direction they are moving.

SPECTROSCOPES

Instruments with a diffraction

grating to study the spectrum

of a star.

A diffraction grating is a piece

of glass or plastic with

thousands of tightly spaced

lines etched on the surface to

produce spectra (different

wavelengths of light).

The spectrum of a star can

determine the stars

composition – what elements

it is made up of.

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CONTINUOUS SPECTRUM

A spectrum having no distinct lines that is

distributed over an unbroken band of wavelengths.

Most continuous spectra are from hot, dense

objects like stars, planets, or moons

ABSORPTION SPECTRUM (dark-line spectrum)

A spectrum that has a pattern of dark

lines due to the light passing through

an absorbing medium; can be used to

identify a material

Each type of atom absorbs a different

wavelength of light and therefore

creates its own absorption spectrum

EMISSION SPECTRUM (bright-line spectrum)

A spectrum that has a pattern of

separate bright lines that is emitted from

an excited gas under low pressure; can

be used to identify a material

A gas will emit the same wavelength of

light that is absorbed during its

excitement

THE ABSORPTION AND EMISSION SPECTRA TOGTHER FOR A GAS SHOULD MAKE A

CONTINUOUS SPECTRUM

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Examples:

1. Use the radiation spectrums to explain what star 1 and star 2 are composed of.

2. Use the following spectral lines to identify the composition of the star.

Hydrogen

Helium

Sodium

Star 1

Star 2

The star is composed of

helium and hydrogen

Star 1 is composed of helium and hydrogen

Star 2 is composed of helium and sodium

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DOPPLER SHIFT

A change in pitch is called the DOPPLER EFFECT and is caused by the change in

a sound’s wavelength.

How does this relate to a star???

If a star is approaching you, its wavelengths become compressed

o So… the dark lines in the stars spectrum shift towards the blue end…BLUE

SHIFTED.

If a star is going away from you, the wavelengths will be longer

o So… The dark lines in the stars spectrum shift towards the red end…. RED

SHIFTED!

The Doppler Effect

Explained…..

before

after

before

after

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EVOLUTION OF STARS

Stars begin in dust clouds

called nebulae.

They condense and heat up

under the influence of gravity.

When it gets hot enough, the

fusion reaction begins.

When the star finally runs out of

fuel, it dies.

The brightness of stars depends

on their mass and temperature

Most stars are called main-

sequence stars

https://www.youtube.com/watch?v=BFplE5EUBzA

NEBULA: an interstellar cloud of

dust and gas

RED SUPERGIANT: a massive star

that has increased in size and

become very bright

SUPERNOVA: a stellar explosion

that produces a very bright cloud

of ionized gas that remains a very

bright object for weeks or months

NEUTRON STAR: a super-dense star

consisting mainly of neutrons

formed as the last stage of an

intermediate-mass star; remnants

of a supernova

PULSAR: a rotating neutron star

that emits radiation in regular

pulses

NEBULA: an interstellar cloud of

dust and gas

RED GIANT: a star of great size and

age that has a relatively low

surface temperature

WHITE DWARF: found in the last

stage of sun-like (low mass) stars -

the star becomes compact as it

collapses; very hot but very faint

BLACK DWARF: hypothetical final

stage of sun-like (low mass) stars –

very cool and invisible

SUN-LIKE STARS MASSIVE STARS

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https://www.youtube.com/watch?v=BFp

lE5EUBzA

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BLACK HOLES

An area in space with a gravitational field so strong that neither matter nor EMR

can escape; formed as the last stage in the evolution of high-mass stars.

Black holes are detected by the gravity effect on nearby stars

Material ripped from nearby stars and falling into a black hole create collisions

with atoms that heat the material to millions of degrees

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Practice Questions:

1. Using the spectra to the right

Which elements make up star A?

(Remember there may be more than

one and they may be slightly shifted)

Hydrogen and mercury

Star B?

hydrogen

Star C?

Sodium and mercury

2. Which direction is star A moving?

Away from you

3. Which direction is star B moving?

Not moving

4. Which direction is star C moving?

Toward you

Practice Questions:

Page 447 33 & 34

33. Astronomical observatories for infrared radiation are sometimes located in special

aircraft that can fly at high altitudes because Earth’s atmosphere absorbs most of the

infrared radiation that arrives from sources in space.

34. A radio telescope is a device that can detect EMR from the radio-wave region of

the electromagnetic spectrum. The energy in the radio waves is used to produce an

electrical signal, which is then used to produce a visible representation of the

information contained in the radio waves. Since radio waves have the longest

wavelengths of all the types of radiation in the electromagnetic spectrum, the dishes

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that collect these waves must be very large. In addition, radio waves are the EMR with

the lowest energy content. A very large reflecting dish means that more radio-wave

energy can be reflected to the detector, allowing for the study of weak signals.

Page 451 35 & 36

35. A continuous spectrum is the full rainbow of colours with no dark lines or bands to

interrupt the flow from one colour to the next. The word continuous refers to the fact

that one colour continues into the next colour, forming an unbroken band of

wavelengths.

When observed through a spectroscope, an emission spectrum consists of a series of

individual bright lines. Each discrete line corresponds to a particular wavelength of

emitted light. Emission spectra are produced when gases under low pressure are

energized by an external source, such as the electric current supplied to a gas-

discharge tube.

When observed through a spectroscope, an absorption spectrum consists of a pattern

of dark lines superimposed on a continuous spectrum. Each dark line corresponds to a

wavelength of light that is absorbed. Absorption spectra are produced when light

passes through a gas at low pressure. The lines that a particular gas will absorb in its

absorption spectrum correspond to the same lines that the gas emits in its emission

spectrum.

36. The evidence supporting the idea that the universe is expanding comes from the

spectral analysis of the light from remote galaxies. In every case, the pattern of spectral

lines has been shifted to the red end of the spectrum. Since red shift indicates that the

source of light is moving away from the observer, every remote galaxy in the universe

must be moving away from Earth. If remote galaxies are increasing their distance from

Earth, the universe must be expanding.

37. Referring to the graph “The Continuous Spectra of Stars:

Brightness of Emitted Light Versus Wavelength” on page 451, you can see the overall

trend is that as the surface temperature of a star rises, the brightness of the emitted light

increases and the peak of the curve moves closer to the blue end of the spectrum. So,

if a star produces light that is less yellow and more white than the light emitted by the

Sun, the surface of this star must have a higher temperature than the surface of the Sun.

Similarly, if a star produces light that is more orange than the light emitted by the Sun,

the surface of this star must have a lower temperature than the surface of the Sun.

38. The feature that determines the endpoint of a star in stellar evolution is the initial

mass of the gas and dust that forms the star. If the initial mass is between 0.1 and 1.4

solar masses, the end result of solar evolution will be a white dwarf. If the initial mass is

between 1.4 and 8 solar masses, the end result of solar evolution will be a neutron star.

Finally, if the initial mass is greater than 8 solar masses, the end result will be a black

hole.

Page 453 37, 38 & 39

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39. A black hole is an area in space with a gravitational field that is so strong that

neither matter nor EMR can escape. A telescope is a device designed to detect the

light emitted or reflected from distant objects. Since no light is emitted from a black

hole, a telescope would be unable to detect it.

Page 455 4, 5 & 6

4. Since the star that produced the Crab Nebula involved a supernova, it must have

been an intermediate-mass star. An intermediate-mass star begins as a cloud of gas

and dust, progresses to form an intermediate-mass star, and eventually forms a

supergiant star before exploding as a supernova and forming a neutron star.

5. Each type of EMR yields unique information about the Crab Nebula. By using as many

types of EMR as possible, scientists obtain a much richer collection of data than if they

studied the Crab Nebula using only one type of radiation.

6. a. The success of an agricultural economy depends upon obtaining the optimal

harvest of the crops that are planted. It is important to know the best times of the year

to plant the seeds, when to expect the seasonal rains, and when to harvest.

Astronomical observations could have provided the ancient Pueblo People (Anasazi)

with an accurate way to keep track of these key periods in the growing season.

b. Given that astronomical observations may have played an important role in their

agricultural economy, it is likely that they were already routinely looking up to the night

sky. It is also likely that the events in the sky were taken quite seriously as their survival

was linked to their ability to record and track changes in the positions of constellations.

However, unlike everyday occurrences, this astronomical event would have been a

truly amazing sight, something completely out of the ordinary. Given these

circumstances, it seems only natural to make a record of such an unusual event.