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Astronomy and the
Electromagnetic Spectrum
Objectives
• Identify the visible and non-visible parts of the electromagnetic
spectrum
• Compare refracting telescopes and reflecting telescopes
• Explain how telescopes for non-visible electromagnetic radiation
differ from light telescopes, and why they are typically launched into
space
The Value of Astronomy
• Astronomy: the scientific study of the universe
• Scientists who study the universe are called astronomers
• In the process of observing the universe, astronomers have made
exciting discoveries, such as new planets, stars, black holes, and
nebulas.
• By studying these objects, astronomers have been able to learn
more about the origin of Earth and the processes involved in the
formation of our solar system.
Why Study Astronomy?
• Astronomy explains the motions of celestial (stars, planets, etc.)
objects in the night sky
• Astronomy allows us to determine the origin and structure of
galaxies, stars (suns) and planets
• Explains how the universe evolved with time
• Studies of how stars shine may one day lead to improved or new
energy sources on Earth.
• Astronomers may also learn how to protect us from potential
catastrophes, such as collisions between asteroids and Earth.
• Astronomical research is supported by federal agencies, such as the
National Science Foundation and NASA. Private foundations and
industry also fund research in astronomy
Characteristics of the Universe
• The Universe is an ever expanding space made up of all
matter, including galaxies, which are often found in
groups and clusters
• Galaxy: a collection of stars/suns, dust, and gas bound
together by gravity.
• Our galaxy is called….The Milky Way
Active Galaxies
Centaurus A
Galaxies and Solar Systems
• Each star within a galaxy is most likely accompanied by a solar
system.
• Our solar system includes the sun, Earth, other planets, and many
smaller objects such as asteroids and comets.
• Can you name the planets which orbit our sun?
The Local Universe - Our Sun
A photograph of the Sun
Ultraviolet image of
erupting prominence
Measuring Distance in Astronomy
• Astronomical unit (AU): the average distance between the Earth
and the sun; approximately 150 million kilometers (km)
– So, 1 AU = 150 million kilometers
– To get an idea of how far that
is….150,000,000km*(1000m/1km)*(3.3ft/1m)(1mile/5280ft)=???
• Astronomers also use the speed of light to measure distance.
• Light travels at 300,000,000 m/s. In one year, light travels 9.4607 x
1012 km. This distance is known as a light-year.
• ALL TYPES OF LIGHT TRAVEL AT THE SAME SPEED
The closet star to Earth (other than our sun!)
is 4.2 light-years away.
How Do We Observe Objects in
Space?
• Objects emit Electromagnetic Radiation
• Electromagnetic Radiation is energy
– Light, radio waves, and X rays are all examples of
electromagnetic radiation.
– The radiation is composed of traveling waves which oscillate
repeatedly move back and forth (oscillate) at fixed frequencies
and wavelengths.
Observing Space
• Electromagnetic Spectrum: all of the wavelengths of
electromagnetic radiation. (EMS Video)
Visible Electromagnetic Radiation
• Though all light travels at the
same speed, each color of light
has a different wavelength. These
colors can be seen when visible
light is passed through a prism.
Elements in Earth’s atmosphere
act as a prism.
• The human eye can see only
radiation of wavelengths in the
visible light range of the
spectrum.
• Electromagnetic radiation shorter
or longer than wavelengths of
visible light cannot be seen by
humans.
• The shortest visible wavelength
of light is violet, while the longest
is red.
Reading check
Which type of electromagnetic radiation can be seen by humans?
The only kind of electromagnetic radiation the human eye can detect is
visible light.
Invisible Electromagnetic
Radiation
• Invisible wavelengths include infrared waves, microwaves, radio
waves, ultraviolet rays, X rays, and gamma rays, and are
detected only by instruments.
• Infrared (IR) means “below the red”, and has waves longer than
waves of visible light.
– Ex. Heat
• Ultraviolet (UV) means “beyond the violet” and has wavelengths
shorter than waves of visible light.
– Ex. Certain light emitted by the sun is UV light, and causes us to
tan or burn if exposed too long to the sun’s rays
Infrared Radiation
• Dust obscures regions of star formation. Certain telescopes can
be used to see through the dust.
Hubble Space Telescope –
Optical image of the Orion Nebula
Anglo-Australian Telescope –
Infrared image
Telescopes
• The telescope is an instrument which collects electromagnetic
radiation concentrates it for better observation.
• In 1609, an Italian scientist, Galileo, heard of a device which used
two lenses to make distant objects appear closer.
• Telescopes which collect only visible light are called optical
telescopes.
• The two types of optical telescopes are:
• refracting telescopes
• reflecting telescopes
Optical Telescopes
•
Refraction: The bending of light
•
Refracting Telescope: uses a set of lenses to gather, bend
and focus light for magnification
•
Two problems with refracting telescopes
1. The lenses focus different colors of light at varied distances which
causes distortion.
1. The lenses are too large which causes images to become
distorted.
•
Reflecting Telescopes: uses a curved mirror to gather, reflect,
and focus light for magnification
•
Unlike refracting telescopes, reflecting telescopes can be made
very large without affecting the quality of the image.
Optical Telescopes
The diagrams below show reflecting and refracting
telescopes.
Telescopes for Invisible
Electromagnetic Radiation
• Scientists have
developed telescopes
which detect invisible
radiation
• Many of these can only
be used from space
because Earth’s
atmosphere acts as a
shield against many
forms of electromagnetic
radiation.
Space-based Telescopes
• In space, Earth’s atmosphere cannot interfere with the telescope’s
detection of electromagnetic radiation.
• These telescopes detect radio waves, gamma rays, x-rays, or
infrared
• Telescopes beyond the atmosphere of the Earth send back much
more detailed information.
• Space-based telescopes include the:
– Hubble Space Telescope: collects Infrared, visible, and
ultraviolet electromagnetic radiation
– Chandra X-ray Observatory
– Compton Gamma Ray Observatory
– James Webb Space Telescope: will detect infrared radiation
after it is launched in 2011