Astronomical Observations

Type AtmosphereRadio Waves No effectMicrowaves Mostly blockedInfrared BlockedVisible Light Slight blurringUltraviolet BlockedX-rays BlockedGamma Rays Blocked

What wavelengths to use?

Incoming Rays

Lens

Outgoing Rays

Focal Plane

Image

Lenses and Light

Light waves going through a lens are bentThey converge on the focal plane of the lensAn image forms on the focal planeThe greater the distance to the focal plane, the bigger the image

EyeObject

Focal Plane

Lens

Working in reverse, a lens can magnify a small object making it look big and far awayThe closer the focal plane is, the bigger the imageYou can also magnify an image

Lenses and Light

EyeFrom Point Source 2

From Point Source 1

Objective Lens Eyepiece

Focal Plane

Two lenses together make a telescopeChanging the eyepiece changes the magnificationThe amount of light gathered depends on the size of the objective

Image of Point 1

Image of Point 2

Lenses and Light

PrismView directlyCCD cameraSpectrometer

The Spectrometer•Uses prism or (more likely) diffraction grating•Breaks light into different colors/wavelengths/frequencies

From the Telescope

What to do with the light

CCD detector

Mirrors and Light

Mirrors can also create images - in some ways, better than lensesLarge telescopes are always reflectors

Focal Plane

MirrorIncoming Rays

Reflected Rays

The largest optical telescopes in the worldGran Telescopio Canarias

10.6 m diameterKeck 1 and Keck 2

10 m diameter each

What makes a good telescopeThe bigger the diameter, the better

Bigger diameter = more light gathering powerBigger diameter = less diffraction (blurring)

Avoid atmospheric distortion and light pollutionSpaceMountainsAway from light pollution

Magnification is not the main issueEyepiece changes magnification

Outside the solar system, you can never decrease the distance

Too far away

Space Based TelescopesSeveral advantages of going to space

No atmospheric distortionNo light pollutionCan see infrared/ultraviolet

Hubble Telescope James Webb Space TelescopeLaunches 2018

Active Optics

It is hard to make large mirrorsIt is easier to make several small mirrorsYou can use motors & computer to line them up

Focal Plane

Mirror

Incoming Rays

Reflected Rays

Adaptive Optics

Light gets distorted by the atmosphereIt ends up imperfect at the telescopeThis ruins the focus, blurring the image

Focal Plane

Mirror

Computers can respond to imperfectionsMotors can adjust the mirrorsThis fixes the blurred image

Focal PlaneMirror

Adaptive Optics

Telescopes are used here on earth to observe visible light from space. Why aren’t they used for infrared and ultraviolet light?A) No astronomical objects produce these kinds of lightB) The atmosphere blocks these types of lightC) No mirrors or lenses have ever been discovered that can reflect/refract these kinds of lightD) Film and CCD cameras can’t detect these types of light

What wavelengths to use?

What wavelengths to use?

Type AtmosphereRadio Waves No effectMicrowaves Mostly blockedInfrared BlockedVisible Light Slight blurringUltraviolet BlockedX-rays BlockedGamma Rays Blocked

Radio Telescopes

Reflector

Incoming Radio Waves

Reflected Radio Waves

Antenna

Always use a radio reflector (like a mirror)High precision reflector is not necessary because radio waves are very longMost radio sources are quite weak

Arecibo Telescope, 305 m

Robert C. Byrd Green Bank Telescope, about 100 m

Radio Telescopes

Radio Interferometry

No atmospheric blurringBackground ProblemHuge diffraction limit problem (about 1o)Signal can be combined from multiple radio telescopesEffective size is distance between telescopesEffective resolution better than optical

Radio Interferometry

Very Large Array

Radio Interferometry

Very Long Baseline Array

What wavelengths to use?

Mostly restricted to spaceLimited microwave and IR from Earth

Type AtmosphereRadio Waves No effectMicrowaves Mostly blockedInfrared BlockedVisible Light Slight blurringUltraviolet BlockedX-rays BlockedGamma Rays Blocked

Infrared and Microwave Space TelescopesSpitzer Space

Telescope

Herschel Observatory

Wilkinson Microwave Anisotropy Probe

Planck Observatory

X-Ray Space TelescopesChandra X-Ray Observatory

XMM Newton

Rossi X-Ray Timing Explorer

Swift Gamma Ray Burst Telescope

UV and Gamma-Ray Space Telescopes

GALEXINTEGRAL

Fermi Gamma-Ray Space Telescope