Chapter 15

Section 1 – pg 590Telescopes

• Telescope was invented in 1608– Makes distant objects appear closer– With a telescope Galileo was the first to see sunspots,

Saturn’s rings, and the four large moons of Jupiter• Since Galileo better telescopes have been invented

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Electromagnetic RadiationElectromagnetic Radiation

• Electromagnetic radiation: Electromagnetic radiation: energy that can travel energy that can travel through space in the form of wavesthrough space in the form of waves– Stars produce this during nuclear fusionStars produce this during nuclear fusion– You see stars when the light they produce reach your You see stars when the light they produce reach your

eyeeye

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Forms of Radiation• Visible light: all the colors you see, a type of

electromagnetic radiation– Many objects give off radiation that you don’t see• Heating coils give off light and infrared radiation (heat)• Radio transmitters produce radio waves that carry signals

radios and tvs

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The Electromagnetic Spectrum• Wavelength: the distance between the crest of one

wave and the crest of the next wave– Visible light’s wavelength is very short • Some are 1 millionths of a meter, others are several

meters long

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• Spectrum: range of different colors with different wavelengths– Visible light is made of red, orange,

yellow, green, blue, indigo, violet• The electromagnetic spectrum

includes the entire range of radio waves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays

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Types of Telescopes• The light from stars spreads out as it moves through

space, and your eyes are too small to gather much light– This is why you cant see as many stars with just your

eyes• Telescopes are instruments that collect and focus light

and other forms of electromagnetic radiation– Optical telescope: a telescope that uses lenses or mirrors to

collect and focus visible light• Refracting telescopes and Reflecting telescopes

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• Modern astronomy is based on the detection of forms of electromagnetic radiation besides visible light– Non-optical telescopes collect and focus different types

of electromagnetic radiation

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Refracting Telescopes• Refracting telescope uses a convex lens to

gather and focus light– Convex lens: a piece of transparent glass, curved so that

the middle is thicker than the edges– Has 2 convex lens (one at each end)– Light enters through large objective lens, which focuses

it a certain distance from the lens• The larger the lens, the more light

it collects

– Smaller lens at lower end is eyepiece, which magnifies the image

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Reflecting Telescope• In 1668, Isaac Newton built the first reflecting

telescope• Reflecting telescope uses a curved mirror to collect and

focus light– Focuses a large amount of light onto a small area– The larger the mirror, the more light the telescope can

collect

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Radio Telescopes• Radio Telescopes: devices used to detect radio waves

from objects in space– Most radio telescopes have curved, reflecting surfaces– The curved surfaces focus faint radio waves from space– The larger a radio telescope, the more radio waves it can

collect

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Other Telescopes• Some telescopes detect infrared radiation– Other detect ultraviolet radiation, X-rays, and gamma

rays

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Observatories• Observatory: a building that contains one or more

telescopes– Some are located in space, many are on mountaintops– Earth’s atmosphere makes objects in space look blurry

• One of the best observatories on Earth is on top of Mauna Kea, a dormant volcano in Hawaii– Taller than 40% of Earth’s atmosphere

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Advanced Telescope• Some new telescopes are equipped with computer

systems that correct images for problems such as telescope movement and changes in air temperature or mirror shape

• Other advanced telescopes uses lasers to monitor conditions in the atmosphere and change the shape of the telescope’s mirror in response

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Telescopes in Space• X-rays, gamma rays and most ultraviolet

radiation are blocked by Earth’s atmosphere– Use telescopes in space

• Hubble Telescope collects ultraviolet, infrared radiation, and visible light

• Chandra X-ray Observatory produces images in the X-ray portion of the spectrum

• Spitzer Space Telescope produces images in the infrared portion of the spectrum

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Chapter 15 Section 1Homework – pg 596

1A. List the main types of electromagnetic waves, from

longest wavelength to shortest.

1B. Why are images from the Hubble Space Telescope clearer

than images on Earth?

2A. What are the two major types of optical telescopes?

2B. How does a refracting telescope work?

2C. Use Figure 2 to explain the major differences between

reflecting and refracting telescopes

3A. How does the atmosphere affect electromagnetic radiation?

3B. Why are many large optical telescopes located on

mountaintops?

3C. Would it make sense to place an X-ray or gamma ray telescope

on a mountaintop? Explain why or why not?