Light, radiation, Light, radiation, telescopestelescopes

Tools of the tradeTools of the trade

Electromagnetic Radiation from Electromagnetic Radiation from distant sourcesdistant sourcesTelescopesTelescopesDetectorsDetectorsComputersComputersLots of hard workLots of hard work

Electromagnetic RadiationElectromagnetic Radiation

Characterized by Characterized by WavelengthWavelengthFrequencyFrequencyAll types travel at All types travel at same speedsame speed……300,000 km/s = c300,000 km/s = c

f = frequency= wavlength

c = speed of light

f cλ

λ

=

Electromagnetic spectrumElectromagnetic spectrum

http://upload.wikimedia.org/wikipedia/commons/c/cf/EM_Spectrum_Properties_edit.svg

Click on images to go to Physics 2000 site!Click on images to go to Physics 2000 site!

Lower frequency waves are caused by oscillating charges

What frequency do electrons in your car antenna oscillate at?

http://www.colorado.edu/physics/2000/waves_particles/wavpart4.html

Telescopes and detectors Telescopes and detectors

First detector: First detector: The EyeThe Eye

The Bending of LightThe Bending of LightFocus – to bend all light waves coming from the same

direction to a single point

Light rays which come from different directions converge at different points to form an image.

Angular ResolutionAngular Resolution

The ability to The ability to separate two objects.separate two objects.The angle between The angle between two objects decreases two objects decreases as your distance to as your distance to them increases.them increases.The smallest angle at The smallest angle at which you can which you can distinguish two distinguish two objects is your objects is your angular resolutionangular resolution..

Types of TelescopesTypes of Telescopes

•• WhatWhat’’s the difference between a s the difference between a refracting telescope and a reflecting refracting telescope and a reflecting telescope?telescope?

•• What are the two most important What are the two most important properties of a telescope?properties of a telescope?

RefractorRefractor

Yerkes 40-inch telescope; largest refractor in the world

Reflecting TelescopeReflecting Telescope

Lick Observatory 2.4 m Planet Finder

Gemini 8 m telescope Hawaii

Different Reflector designsDifferent Reflector designs

Best type to buy? Best type to buy?

Dobsonian! Dobsonian! Most Bang for buckMost Bang for buckLarge aperatureLarge aperatureRelatively lightRelatively lightRelatively cheapRelatively cheapEasy to maneuverEasy to maneuverEasy to fixEasy to fix

College scopesCollege scopes

1414”” Schmidt CassegrainSchmidt CassegrainCorrector plateCorrector plateCompact designCompact designTrackingTrackingNot cheapNot cheap

Build your own scope?Build your own scope?

Chabot Science Center Telescope Chabot Science Center Telescope makers workshop: makers workshop: http://www.chabotspace.org/visit/telhttp://www.chabotspace.org/visit/telescopeworkshop.aspescopeworkshop.asp

Space telescopesSpace telescopesWhy Why bother?bother?

1.1. To improve To improve resolving resolving power power (seeing)(seeing)

2.2. Observe non Observe non visible visible wavelengthswavelengths

SeeingSeeingDue to turbulence in Due to turbulence in atmosphereatmosphereLimits resolving power to size Limits resolving power to size of seeing diskof seeing diskAbout About ½½ arc second maximum arc second maximum for for ““normalnormal”” observing (no observing (no adaptive optics) adaptive optics) With no atmosphere, seeing is With no atmosphere, seeing is about .01 arc seconds for 10 m about .01 arc seconds for 10 m telescopetelescope

=wavelength, D = Diameter of objective (mirror)Dλθ

λ

≈

http://upload.wikimedia.org/wikipedia/commons/e/ef/Seeing_Moon.gif

Seeing Disks of Binary StarsSeeing Disks of Binary Stars

above are what two binary stars separated by 1 degree would look like if photographed by Different sized telescopes…largest on left, smallest on right. Hubble images on right

More Hubble imagesMore Hubble images

.1 arc second Seeing! .1 arc second Seeing!

Spitzer IR telescopeSpitzer IR telescope85 cm aperture85 cm apertureTrails earth in Trails earth in orbitorbitCooledCooledWavelength Wavelength between 3 between 3 –– 180 180 micronsmicrons

MultiMulti--wavelength imageswavelength images

Combine light from visible and IR Combine light from visible and IR telescopes! telescopes!

How to improve Resolving powerHow to improve Resolving power

At 1m, telescopes on ground are At 1m, telescopes on ground are already already ““diffraction limiteddiffraction limited”” by size by size of seeing diskof seeing diskSoSo……Build bigger telescope in spaceBuild bigger telescope in spaceOr correct for atmospheric distortionOr correct for atmospheric distortionUse adaptive opticsUse adaptive optics

Next Generation Next Generation James James Web Web space space telescopetelescope6.5 meter6.5 meterApertureApertureLaunch Launch 20112011Note Note large sun large sun shieldshield

Adaptive opticsAdaptive optics

Taking out the twinkle! Taking out the twinkle!

Image of a star “dancing” on detector due to motion of air

http://antwrp.gsfc.nasa.gov/apod/image/0007/AlphaOri_cardiff.gif

Laser Guide star systemLaser Guide star system

Laser Laser ““scintillatesscintillates””atoms in atoms in ionosphereionosphereOptical system Optical system brings artificial brings artificial star into focus.star into focus.

http://antwrp.gsfc.nasa.gov/apod/image/0502/laser_keck_big.jpg

other wavelength astronomyother wavelength astronomy

Radio Astronomy Radio Astronomy Uses much larger Uses much larger aperaturesaperatures——why?why?Ultraviolet, XUltraviolet, X--Ray, Gamma RayRay, Gamma Ray

http://antwrp.gsfc.nasa.gov/apod/image/0810/cta1_fermi_big.jpg

In futureIn futureGigantic Earth Gigantic Earth based optical based optical telescopes with telescopes with adaptive optics adaptive optics systemssystems

More More InterferometersInterferometers

Light, radiation, telescopesTools of the tradeElectromagnetic RadiationElectromagnetic spectrumClick on images to go to Physics 2000 site! Telescopes and detectors The Bending of Light�Angular ResolutionTypes of TelescopesRefractorReflecting TelescopeDifferent Reflector designsBest type to buy? College scopesBuild your own scope?Space telescopesSeeingSeeing Disks of Binary StarsMore Hubble imagesSpitzer IR telescopeMulti-wavelength imagesHow to improve Resolving powerNext Generation Adaptive opticsLaser Guide star systemother wavelength astronomyIn future