AST 103TelescopesProf. Ken Nagamine

UNLV

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Telescopes

Mauna Kea, Hawaii

• The best observing sites are atop remote mountains

Calm, High, Dark, Dry

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There are two different types of telescopes

• A refracting telescope: focuses light with glass lenses

• A reflecting telescope: focuses light with mirrors

A telescopes is a tool used to gather light from objects in the universe

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A refracting telescope uses a lens to focus incoming light

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Refraction• Refraction is the

bending of light when it passes from one substance into another

• Your eye uses refraction to focus light

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Focusing Light

• Refraction can cause parallel light rays to converge to a focus

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Refracting Telescope

• Refracting telescopes need to be very long, with large, heavy lenses

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Reflecting Telescope

• Reflecting telescopes can have much greater diameters

• Most modern telescopes are reflectors

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Reflecting telescopes use mirrors to focus incoming starlight

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Mirrors in Reflecting Telescopes

Twin Keck telescopes on Mauna Kea in Hawaii

Segmented 10-meter mirror of a Keck telescope

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Many big telescopes!!

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Three main functions of a telescope

• gather light – (bigger IS better) – makes objects appear brighter

• see fine detail (resolution)

•magnify

Telescopes that are larger are capable of taking images with greater detail.

Telescopes with a larger collecting area can gather a greater amount of light in a shorter time.

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A larger objective lens provides a brighter (not

bigger) image

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But visible light is just one part of spectrum

Astronomers are interested in the entire spectrum of light!

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Astronomers use different instruments to look at light of different wavelengths - sometimes, we even have to

go above Earth’s atmosphere.15

Quiz

Which of the following wavelengths can be observed easily by a telescope located on Earth’s surface?

a) gamma ray b) X-ray c) ultraviolet d) radio e) all of the above wavelengths f) none of the above wavelengths

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IR & UV Telescopes

• Infrared and ultraviolet-light telescopes operate like visible-light telescopes but need to be above atmosphere to see all IR and UV wavelengths

SOFIA (IR)

Spitzer (IR)GALEX (UV)

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Radio wavelength observations are possible from Earth’s surface

Arecibo, Puerto Rico

Green Bank(west virginia)

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The Very Large Array (VLA) in New Mexico

Interferometer19

High above Earth’s

atmosphere, the Hubble Space

Telescope provides

stunning details about the universe

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Earth’s atmosphere hinders astronomical researchImage of stars taken with a telescope on the Earth’s surface

Same picture taken with Hubble Space Telescope high above Earth’s blurring atmosphere

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Lecture-Tutorial (LT):Telescopes (pp. 49-51)

• Work with a partner!

• Read the instructions and questions carefully.

• Discuss the concepts and your answers with one another.

• Come to a consensus answer you both agree on.

• If you get stuck or are not sure of your answer, ask another group.

• If you get really stuck or don’t understand what the LT is asking, ask for help.

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Which of the following wavelengths of light emitted by the Sun is most effectively blocked by Earth’s atmosphere?

a) visible b) radio c) infrared d) gamma

Quiz

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Imagine that you are the head of a funding agency that can afford to build one telescope. Which of the following proposed telescopes would be best to support?

a) a radio telescope in orbit around Earth

b) an ultraviolet telescope in orbit around Earth

c) an X-ray telescope located in New Mexico

Quiz

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The Hubble Space Telescope obtains higher resolution images than most ground-based telescopes because it is

a) larger. b) closer to stars.c) above Earth’s atmosphere.

Quiz

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