Light and Telescopes What do you think? What is the main purpose of a telescope? Why do stars twinkle? 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 ...
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 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) 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! Not all EM radiation can penetrate Earths atmosphere. Astronomers use different instruments to look at
light of different wavelengths - sometimes, we even have to go above Earths atmosphere. SOFIA - the Stratospheric Observatory for Infrared Astronomy Observations at other wavelengths are revealing previously invisible sights
UV Ordinary visible infrared Map of
Orion region Consider Orion in Different Wavelengths of Light! http://www.cnn.com/2001/LAW/02/20/scotus.heatdetector.01.ap/index.html Hubble Space Telescope Views of Orion Nebula showing stars hidden in clouds
http://oposite.stsci.edu/pubinfo/pr/97/13/A.html TODAYS Sun as seen in visible light from Earth and from space in X-rays by satellites http://solar.physics.montana.edu/tslater/real-time/ Observations at wavelengths other than visible
light are revealing previously invisible sights Visible light image radio wavelength image High Energy Gamma Rays - Compton Gamma Ray Observatory (GRO) Satellite
The Skys emission of Gamma Rays But, we receive GRBs from every direction !! The fact that GRBs come from every direction imply that GRBs dont come from our galaxy, but from other galaxies spread in every direction!
Radio wavelength observations are possible from Earths surface The Very Large Array (VLA) in New Mexico 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 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. 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! blue 4600 A
81 Filter Detector 81
blue 4600 A green 5300 A 81 85 Filter
Detector 85 blue 4600 A green 5300 A yellow 5800 A
81 85 83 Filter Detector 83
blue 4600 A green 5300 A yellow 5800 A orange 6100 A 81 85
83 78 Filter Detector 78
blue 4600 A green 5300 A yellow 5800 A orange 6100 A red 6600 A
81 85 83 78 70 The spectrum is continuous. Filter
Detector 70 UV IR
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. A refracting telescope uses a lens to concentrate incoming light
Similar to a magnifying glass A larger objective lens provides a brighter (not bigger) image
lenses reverse images 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) 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) Refracting telescopes have drawbacks
Spherical aberration Chromatic aberration Special achromatic compound lenses and lens coatings can often fix this aberration 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
Reflecting telescopes use mirrors to concentrate incoming starlight Newtonian Focus Prime Focus Cassegrain focus
coude focus Astronomers face two major obstacles in observing the stars Light Pollution from Cities Effects of Twinkling from Earths atmosphere Tucson, Arizona in 1959 and 1980
Earths atmosphere hinders astronomical research Image of stars taken with a telescope on the Earths surface Same picture taken with Hubble Space Telescope
high above Earths blurring atmosphere Rapid changes in the density of Earths atmosphere cause passing starlight to quickly change direction, making stars appear to twinkle.
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 Earths atmosphere Orbiting space observatories A Charge-Coupled Device (CCD)
Ordinary Photographs vs. CCDs Film (negative) CCD (negative) CCD (positive)
Same integration (I.e. exposure) time. Different quantum efficiency: Film 1% CCD 70% Matching 10-m, multiple mirror Keck Telescopes in Hawaii with adaptive optics High above
Earths atmosphere, the Hubble Space Telescope provides stunning details about
the universe 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 Earths atmosphere cause passing starlight to change direction, making stars appear to twinkle.
