Warm Up 5/29/08

1. Warm Up 5/29/08 • What does a prism do? a. separates sunlight into ultraviolet and infrared radiation b. separates visible light into several colors c. changes the wavelength of electromagnetic waves d. combines the colors of visible light into white light • 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. • Large Doppler shifts indicate ____. a. high speeds c. low speeds b. low temperatures d. high temperatures Answers: 1) b. 2) b. 3) a.

2. Tools for Studying Space Chapter 24, Section 2

3. Refracting 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

4. Simple Refracting Telescope

6. Concept 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.

7. Reflecting 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

8. Viewing Methods with Reflecting Telescopes

9. Concept 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.

10. Detecting 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!)

11. Radio Telescopes

12. Concept Check • Why can radio telescopes be used 24 hours a day? • They do not need visible light to obtain images.

13. Space 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

14. Hubble Space Telescope

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