Download Section 1 Viewing the Universe Chapter 26

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Section 1 Viewing the Universe
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.
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 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
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Organization of the Universe
galaxy a collection of stars, dust, and gas bound together by gravity
 The solar system includes the sun, Earth, the other planets, and many
smaller objects such as asteroids and comets.
 The solar system is part of a galaxy.
 The galaxy in which the solar system resides is called the Milky Way
galaxy.
 The nearest part of the universe to Earth is our solar system.
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Measuring Distances in the Universe
astronomical unit the average distance between the Earth and the sun;
approximately 150 million kilometers (symbol, AU)
 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.
 Aside from the sun, the closet star to Earth is 4.2 light-years away.
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Electromagnetic Spectrum
electromagnetic spectrum all of the frequencies or wavelengths of
electromagnetic radiation.
 Light, radio waves, and X rays are all examples of electromagnetic
radiation.
 The radiation is composed of traveling waves of electric and magnetic
fields that oscillate at fixed frequencies and wavelengths.
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Visible Electromagnetic Radiation
 Though all light travels at the same speed, different colors of light
have different wavelengths. These colors can be seen when visible
light is passed through a spectrum.
 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
violet or red light cannot be seen by humans.
 The shortest visible wavelength of light are blue and violet, while
the longest visible wavelength of light are orange and red.
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Which type of electromagnetic radiation can be seen by
humans?
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Which type of electromagnetic radiation can be seen by
humans?
The only kind of electromagnetic radiation the human
eye can detect is visible light.
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Invisible Electromagnetic Radiation
 Invisible wavelengths cannot be seen by the human eye. They
include infrared waves, microwaves, radio waves, ultraviolet rays, X
rays, and gamma rays, and are detected only by instruments.
 In 1852, a scientist named Sir Frederick William Herschel
discovered infrared, which means “below the red.”
 Infrared is electromagnetic radiation that has waves longer than
waves of visible light. Ultraviolet means “beyond the violet” and
has wavelengths shorter than waves of visible light.
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telescope an instrument that collects electromagnetic radiation from the
sky and concentrates it for better observation.
 In 1609, an Italian scientist, Galileo, heard of a device that used two
lenses to make distant objects appear closer.
 Telescopes that collect only visible light are called optical telescopes.
 The two types of optical telescopes are refracting telescopes and
reflecting telescopes.
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Refracting Telescopes
refracting telescope a telescope that uses a set of lenses to gather and focus
light from distant objects
 The bending of light is called refraction.
 Refracting telescopes have an objective lens that bends light that passes
through the lens and focuses the light to be magnified by an eyepiece.
 One problem with refracting telescopes is that the lens focuses different
colors of light at different distances causing the image to distort.
 Another problem is that objective lenses that are too large will sag under
their own weight and cause images to become distorted.
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Reflecting Telescopes
reflecting telescopes a telescope that uses a curved mirror to gather and focus
light from distant objects
 In the mid-1600s Isaac Newton solved the problem of color separation that
resulted from the use of lenses.
 When light enters a reflecting telescope, the light is reflected by a large curved
mirror to a second mirror. The second mirror reflects the light to the eyepiece,
where the image is magnified and focused.
 Unlike refracting telescopes, reflecting telescopes can be made very large
without affecting the quality of the image.
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The diagram below shows reflecting and refracting telescopes.
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What are the problems with refracting telescopes?
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What are the problems with refracting telescopes?
Images produced by refracting telescopes are subject to
distortion because of the way different colors of visible
light are focused at different distances from the lens
and because of weight limitations on the objective
lens.
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Telescopes for Invisible Electromagnetic Radiation
 Scientists have developed telescopes that detect invisible radiation,
such as a radiotelescope for radio waves.
 Ground-based telescopes work best at high elevations, where the air is
dry.
 The only way to study many forms of radiation is from space because
the Earth’s atmosphere acts as a shield against many forms of
electromagnetic radiation.
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 Spacecrafts that contain telescopes and other
instruments have been launched to investigate
planets, stars, and other distant objects
 In space, Earth’s atmosphere cannot interfere with
the detection of electromagnetic radiation.
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Why do scientists launch spacecraft beyond Earth’s
atmosphere?
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Why do scientists launch spacecraft beyond Earth’s
atmosphere?
Scientists launch spacecraft into orbit to detect radiation screened out
by Earth’s atmosphere and to avoid light pollution and other
atmospheric distortions.
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Space Telescopes
 The Hubble Space Telescope collects electromagnetic radiation from
objects in space.
 The Chandra X-ray Observatory makes remarkably clear images using
X rays from objects in space, such as remnants of exploded stars.
 The Compton Gamma Ray Observatory detected gamma rays from
objects, such as black holes.
 The James Webb Space Telescope will detect infrared radiation from
objects in space after it is launched in 2011.
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Other Spacecraft
 Since the early 1960s, spacecraft have been sent out of Earth’s orbit to study
other planets.
 The Voyager 1 and Voyager 2 spacecraft investigated Jupiter, Saturn, Uranus,
and Neptune, and collected images of these planets and their moons.
 The Galileo spacecraft orbited Jupiter and its moons from 1995 to 2003.
 The Cassini-Huygens spacecraft will study Titan, Saturn’s largest moon. Like
Earth, Titan has an atmosphere that is rich in nitrogen. Scientists hope to
learn more about the origins of Earth by studying Titan.
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Human Space Exploration
 Spacecraft that carry only instruments and computers are described as
robotic and can travel beyond the solar system.
 The first humans went into space in the 1960’s. Between 1969 and 1972,
NASA landed 12 people on the moon. Humans have never gone
beyond Earth’s moon.
 The loss of two space shuttles and their crews, the Challenger in 1986
and the Columbia in 2003, have focused public attention on the risks of
human space exploration.
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Spinoffs of the Space Program
 Satellites in orbit provide information about weather all over Earth.
 Other satellites broadcast television signals from around the world or
allow people to navigate cars and airplanes.
 Even medical equipment, like the heart pump, have been improved
based on NASA’s research on the flow of fluids through rockets.