Download 10.4 Observing the Universe

Section: 10.4
Date:
Essential
Questions
Observing the Universe
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Constellations 
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Optical
Telescopes
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Radio
Telescopes
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Space
Telescopes
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The LightYear
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What is a constellation?
How do optical telescopes differ?
What are the similarities between radio telescopes and optical telescopes?
For a long time, people have looked up in the sky and seen patterns that they named
after characters in stories, animals, and other common things.
Many of the names given to these groups of stars by ancient cultures remain today
and are called constellations.
Astronomers use constellations to locate and name stars. Ancient cultures used
them to navigate from place to place, to create calendars, and to predict changes in
the seasons.
The constellations visible in the sky change throughout the year.
Telescopes are used to study stars and other objects in space.
Optical telescopes collect more light from distant objects than the unaided eye,
producing brighter and clearer images.
A refracting telescope uses a convex lens, which is curved outward like a ball, to
collect and focus visible light.
A reflecting telescope uses mirrors to collect and focus visible light.
Like visible light, radio waves are a form of electromagnetic radiation emitted by
stars and other objects in space.
A radio telescope collects and amplifies radio waves so we can see objects even on
cloudy days.
Astronomers can avoid the blurring effects of Earth’s atmosphere by placing
telescopes in space.
In 1990, the Hubble Space Telescope was placed in orbit around Earth. It has been
used to obtain clearer images of space objects than those obtained by most groundbased telescopes.
Other space telescopes such as the Chandra X-Ray Observatory and the Spitzer
Space Telescope produce images using wavelengths that are absorbed by the
atmosphere.
Light travels a speed of 300,000 km/s in space.
Light from the Sun takes 8 minutes and 20 seconds to travel to Earth, a distance of
approximately 150 million kilometers.
Some objects are so far away it takes millions or billions of years for light from
these objects to reach Earth.
A light-year is the distance light travels in one year – about 9.5 trillion kilometers.
Spectroscopes 
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Example
The visible light from stars can provide information about the star’s composition, its
surface temperature, and even how fast it is moving toward or away from Earth.
The light produced by stars and other objects in space is made of different
wavelengths of visible light.
The wavelengths produced by a star, for example, depend on the star’s temperature
and composition.
A spectroscope uses a prism or diffraction grating to separate light into its
component wavelengths. The spectrum can be used to determine the temperature
and composition of the star.
Astronomers use the spectra of known elements and stars and compare them to that
of an unknown to figure out which elements are in the mystery star.