Light and Telescopes www.assignmentpoint.com

What do you think? What is the main purpose of a telescope? Why do stars twinkle? www.assignmentpoint.com

What is Light and Why Would Astronomers Want to Study the Properties of Light? Sometimes we say light is made of waves Sometime we say light is made of particles called photons Moves very fast, at 186 000 miles per second 300,000 km per second consider a prism ... www.assignmentpoint.com

If you pass white light through a prism, it separates into its component colors. long wavelengths short wavelengths R.O.Y. G. B.I.V spectrum www.assignmentpoint.com

Analyzing The Properties of Light Visible Light is but one part of the entire electromagnetic (EM) spectrum. EM Spectrum includes all kinds of light radio waves (all light moves at the same speed - micro waves light speed) infrared light visible light ultra violet light (some light photons have x rays shorter wavelengths gamma rays and more energy than others) www.assignmentpoint.com

Visible light is only one type of electromagnetic radiation emitted by stars Each type of EM radiation travels at exactly the same speed - the speed of light! www.assignmentpoint.com

Not all EM radiation can penetrate Earth’s atmosphere. www.assignmentpoint.com

Astronomers use different instruments to look at light of different wavelengths - sometimes, we even have to go above Earth’s atmosphere. www.assignmentpoint.com

SOFIA - the Stratospheric Observatory for Infrared Astronomy www.assignmentpoint.com

Observations at other wavelengths are revealing previously invisible sights UV infrared Map of Orion region Ordinary visible www.assignmentpoint.com

Consider Orion in Different Wavelengths of Light! www.assignmentpoint.com

http://www. cnn. com/2001/LAW/02/20/scotus. heatdetector. 01. ap/index http://www.cnn.com/2001/LAW/02/20/scotus.heatdetector.01.ap/index.html www.assignmentpoint.com

Hubble Space Telescope Views of Orion Nebula showing stars hidden in clouds http://oposite.stsci.edu/pubinfo/pr/97/13/A.html www.assignmentpoint.com

TODAY’S Sun as seen in visible light from Earth and from space in X-rays by satellites www.assignmentpoint.com

Observations at wavelengths other than visible light are revealing previously invisible sights Visible light image radio wavelength image www.assignmentpoint.com

High Energy Gamma Rays - Compton Gamma Ray Observatory (GRO) Satellite www.assignmentpoint.com

The Sky’s emission of Gamma Rays www.assignmentpoint.com

But, we receive GRBs from every direction !! The fact that GRBs come from every direction imply that GRBs don’t come from our galaxy, but from other galaxies spread in every direction! www.assignmentpoint.com

Radio wavelength observations are possible from Earth’s surface www.assignmentpoint.com

The Very Large Array (VLA) in New Mexico www.assignmentpoint.com

Different types of EM radiation require different types of telescopes A refracting telescope uses a lens to concentrate incoming light A reflecting telescope uses mirrors to concentrate incoming starlight www.assignmentpoint.com

Analyzing Spectra: The Properties of Light Visible Light is one part of the electromagnetic (EM) spectrum. EM radiation is described as a wave with wavelengths in the range 1x10-15 m to 100 m. Visible light is only a tiny small part of the entire electromagnetic spectrum. Little bits of light are called photons. www.assignmentpoint.com

Dividing Light Into a Spectrum Astronomers separate out light into its individual components using a diffraction grating or using a prism - then they analyze each part independently! www.assignmentpoint.com

blue 4600 A 81 Filter Detector 81 www.assignmentpoint.com

blue 4600 A 81 green 5300 A 85 Filter Detector 85 www.assignmentpoint.com

blue 4600 A 81 green 5300 A 85 yellow 5800 A 83 Filter Detector 83 www.assignmentpoint.com

blue 4600 A 81 green 5300 A 85 yellow 5800 A 83 orange 6100 A 78 Filter Detector 78 www.assignmentpoint.com

The spectrum is continuous. green 5300 A 85 yellow 5800 A 83 blue 4600 A 81 The spectrum is continuous. green 5300 A 85 yellow 5800 A 83 orange 6100 A 78 Filter red 6600 A 70 Detector 70 UV IR www.assignmentpoint.com

Spectra Most light sources contain energy in lots of different wavelengths. We can measure the brightness in various wavelength bands--the result is called the spectrum. The spectrum (total character of light emitted) can tell us a lot about a source. www.assignmentpoint.com

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A refracting telescope uses a lens to concentrate incoming light Similar to a magnifying glass www.assignmentpoint.com

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A larger objective lens provides a brighter (not bigger) image www.assignmentpoint.com

lenses reverse images www.assignmentpoint.com

Three main functions of a telescope Brighten (called light gathering power) See fine detail (called resolution) and least important, Magnify magnification = (objective lens focal length / eyepiece lens focal length) www.assignmentpoint.com

Functions of a Telescope To gather light. want a large objective range of few inches to 10 meters!! To resolve fine detail. limited by size and atmospheric “seeing” To magnify least important about 50x per inch of aperture (rule of thumb) 1: List the major regions of the electromagnetic spectrum in order of wavelength and give common examples of each. 2: List the colors of the visible spectrum in order of wavelength. 3: Name the two main classes of telescopes and describe the physical laws that each uses to form images. 4: Describe how the focal length and diameter of a telescope influence its angular resolution, light-gathering power, and magnifying power. 5: Draw a refracting telescope and reflecting telescopes with Newtonian, Cassegrain, prime, and coude’ focus locations, showing the path of parallel light rays through each. 6: Compare the merits and deficiencies of the two major classes of telescopes. 7: Discuss the similarities and differences of radio telescopes and optical telescopes. 8: List the advantages of orbiting telescopes over Earth-bound telescopes in detecting electromagnetic radiation in each of the major spectral regions. 9: Identify examples of observations impossible from the ground that have been made by the Hubble Space Telescope. www.assignmentpoint.com

Refracting telescopes have drawbacks Spherical aberration Chromatic aberration www.assignmentpoint.com

Special achromatic compound lenses and lens coatings can often fix this aberration www.assignmentpoint.com

Refracting telescopes have drawbacks Spherical aberration Chromatic aberration Sagging due to gravity distorting the lens Unwanted refractions opaque to certain wavelengths of light Yerkes Observatory - 40-inch Refracting Telescope: The Largest Refracting Telescope in the World www.assignmentpoint.com

Reflecting telescopes use mirrors to concentrate incoming starlight www.assignmentpoint.com

Cassegrain focus Newtonian Focus coude’ focus Prime Focus www.assignmentpoint.com

Astronomer’s face two major obstacles in observing the stars Light Pollution from Cities Effects of Twinkling from Earth’s atmosphere www.assignmentpoint.com

Tucson, Arizona in 1959 and 1980 www.assignmentpoint.com

Earth’s atmosphere hinders astronomical research Image of stars taken with a telescope on the Earth’s surface Same picture taken with Hubble Space Telescope high above Earth’s blurring atmosphere www.assignmentpoint.com

Rapid changes in the density of Earth’s atmosphere cause passing starlight to quickly change direction, making stars appear to twinkle. www.assignmentpoint.com

Advanced technology is spawning a new generation of equipment to view the universe CCDs (charge-coupled devices) Large telescopes on remote mountain tops Mauna Kea in Hawaii Cerro Pachon in Chile Adaptive Optics to counteract the blurring of Earth’s atmosphere Orbiting space observatories www.assignmentpoint.com

A Charge-Coupled Device (CCD) www.assignmentpoint.com

Ordinary Photographs vs. CCDs Film (negative) CCD (negative) CCD (positive) Same integration (I.e. exposure) time. Different quantum efficiency: Film 1% CCD 70% www.assignmentpoint.com

Matching 10-m, multiple mirror Keck Telescopes in Hawaii with adaptive optics www.assignmentpoint.com

High above Earth’s atmosphere, the Hubble Space Telescope provides stunning details about the universe www.assignmentpoint.com

What did you think? What is the main purpose of a telescope? A telescope is designed to collect as much light as possible. It also improves resolution and magnifies images. Why do stars twinkle? Rapid changes in the density of Earth’s atmosphere cause passing starlight to change direction, making stars appear to twinkle. www.assignmentpoint.com