Warm Up 5/29/08Warm Up 5/29/081) What does a prism do?

a. separates sunlight into ultraviolet and infrared radiationb. separates visible light into several colorsc. changes the wavelength of electromagnetic wavesd. combines the colors of visible light into white light

2) What will happen to an object’s wavelength as the object moves toward you?a. The wavelength will vary.b. The wavelength will be shortened.c. The wavelength will not change. d. The wavelength will be lengthened.

3) Large Doppler shifts indicate ____.a. high speeds c. low speedsb. low temperatures d. high temperatures

Answers: 1) b. 2) b. 3) a.Answers: 1) b. 2) b. 3) a.

Tools for Studying SpaceTools for Studying Space

Chapter 24, Section 2Chapter 24, Section 2

Refracting TelescopesRefracting Telescopes Refracting Telescope – a telescope that uses a

lens to bend and concentrate the light from distant objects

The most important lens in a refracting telescope, the objective lens, produces an image by bending light from a distant object so that the light converges at an area called the focus

For an object such as a star, the image appears as a point of light; for nearby objects, it appears as an inverted replica of the original

Astronomers usually study an image from a telescope by first photographing the image

Chromatic Aberration – the property of a lens whereby light of different colors is focused at different places

Simple Refracting TelescopeSimple Refracting Telescope

Concept CheckConcept Check

What is chromatic aberration? Chromatic aberration is an effect

associated with refracting telescopes that weakens an image and produces a halo of color around it.

Reflecting TelescopesReflecting Telescopes Reflecting Telescope – a telescope that

concentrates light from distant objects by using a concave mirror

Because the focus of a reflecting telescope is in front of the mirror, an observer must be able to view the image without blocking too much incoming light

Most large optical telescopes are reflectors; light does not pass through a mirror so the glass for a reflecting telescope does not have to be of optical quality

Both refracting and reflecting telescopes have three properties that aid astronomers in their work: 1) light-gathering power, 2) resolving power, and 3) magnifying power

Another advantage of telescopes with large objectives is their great resolving power, which allows for sharper images and finer detail

To find the magnification, divide the focal length of the objective by the focal length of the eyepiece

Viewing Viewing Methods with Methods with

Reflecting Reflecting TelescopesTelescopes

Concept CheckConcept Check

What is light-gathering power? Light-gathering power refers to the

telescope’s ability to intercept more light from distant objects, thereby producing brighter images.

Detecting Invisible RadiationDetecting Invisible Radiation A narrow band of radio waves is able to penetrate

the atmosphere, by measuring these waves we can map the galactic distribution of hydrogen

Radio Telescope – a telescope designed to make observations in radio wavelengths

A radio telescope focuses the incoming radio waves on an antenna, which absorbs and transmits these waves to an amplifier, just like a radio antenna

Large dishes are necessary to intercept an adequate signal from celestial sources

Radio telescopes are less affected by turbulence in the atmosphere, clouds, and the weather; viewing is possible 24 hours a day; they can “see” through interstellar dust clouds that obscure visible wavelengths

Radio telescopes have revealed spectacular events (the collision of two galaxies!)

Radio TelescopesRadio Telescopes

Concept CheckConcept Check

Why can radio telescopes be used 24 hours a day?

They do not need visible light to obtain images.

Space TelescopesSpace Telescopes Space telescopes orbit above Earth’s

atmosphere and thus produce clearer images than Earth-based telescopes

The first space telescope, built by NASA, was the Hubble Space Telescope (put into orbit in 1990)

Hubble and other telescopes have detected more than 140 extrasolar planets (a planet orbit around a star other than the sun)

A planet’s gravity causes a Doppler shift in light emitted by the planet’s star

Space telescopes are designed often to observe objects in space at wavelengths outside the visible spectrum; this allows astronomers to classify objects and to study how they formed

Hubble Space TelescopeHubble Space Telescope

AssignmentAssignment Read Chapter 24, Section 2 (pg. 678-683)Read Chapter 24, Section 2 (pg. 678-683) Do Chapter 24 Assessment #1-34Do Chapter 24 Assessment #1-34