New Improved Eyes

Telescopes and “Invisible” Astronomy

Galileo ReduxGalileo first used the telescope to make

important observationsAn optical telescope since it used visible

portion of spectrumAll telescopes are “light buckets”Stellar Parallax is finally seen (1830’s)Cosmological Models were refined

OpticsWhen light passes from one transparent

material (medium) to another its speed changes (Water, glass)

This causes REFRACTION (bending) of the light rays

Rainbows, “broken” pencilsDoes depend on Wavelength of light

Refraction

Air

Water

OpticsWhen light hits a polished opaque

surface, it is REFLECTED with no change in speed

Mirrors, shiny metallic objectsLight will bounce off at the same angle

that it came inDoesn’t depend on wavelength of light

Reflection

Mirror

40º 40º

Image Formation Light is reflected or given off by objectsLens and Mirrors can be used to direct

and focus this lightLenses use refractionMirrors use reflectionWhen light rays return to same relative

positions they started at from the object, an image is formed

Image FormationFor very distant objects (stars, galaxies,

planets) this light is focused at the focal point of the lens or mirror

This image is then transferred to the detector (eye, photographic plate, CCD)

The image forms at the distance of the focal length from the lens or mirror

Telescopes3 parts

Objective Instrument

Mount

The Jobs of a TelescopeLight Gathering Power –Most important

Determined by Area of the Objective LensResolution-

Determined by Diameter of the Objective Lens

Magnification-Least Important Determined by Focal Length of Eyepiece

TelescopesUse lenses and/or mirrors Objective (Lens or Mirror) –focuses lightPrime Focus-focal point of objectiveEyepiece (Lens) or other Instruments

capture image Doesn’t have to be an “optical” image

Telescopes

RefractorLens objective

Think long and skinny How do they work?

ReflectorMirror Objective

Think short and stout How do they work?

Both can have lens eyepiece

Refractor Problems Big Glass costs Big $$$ Must be large to focus light

Unstable and Difficult to move

Chromatic Aberration Spherical Aberration Absorption of light Big Glass is heavy leading to saggy lenses Imperfections in Glass, bubbles, cracks etc.

Reflector ProblemsDo not have Chromatic Aberration,

absorptions, size or imperfection problems

Still have spherical aberration but this can be corrected with an extra attachment (Schmidt Corrector Plate)

All big telescopes are reflectors, some containing “fish-eye” mirrors

Reflectors

Keck 1

Fish eye mirror

Reflector

Hobby-Eberly Telescope helped pioneer the fisheye technology

Telescope still works after one of the mirrors was shot!

Solar Telescope

Telescope’s Job DescriptionAll telescopes perform same jobsGather Light

Light Gathering Power-Area of Objective Resolve Detail

Resolution-Diameter of ObjectiveMagnify Image

Focal Length of Eyepiece

Invisible AstronomyMany wavelengths we can’t seeSpecial telescopes can “see” themOptical Telescopes (Keck)Radio Telescopes (VLA)X-ray Telescopes (Chandra)UV (Fuse) Infrared (IRTF)

Chandra X-ray Observatory

Orbiting X-ray telescope searching for high energy objects such as Black Holes

Invisible AstronomyMuch more informationDifferent types of situations make

different wavelengths of lightOne object, observed at different

wavelengths can provide new insights It may look quite different at the different

wavelengths

Sun at Several Wavelengths

X-ray

EUV

UV

Visible

http://umbra.nascom.nasa.gov/images/latest.html

Radio TelescopesCan be used singly or in groupsBigger “eye” – more sensitiveCan observe night and day, rain or

shineGrouping-Interferometry Improves resolution

Very Large Telescope

Arecibo Radio Telescope is the largest on Earth at 1000 ft wide

Astronomy Picture of the Day

Very Large Array

27 “house sized” radio antennae that can be move on railroad tracks

They span an area equal to a small city in land area

Astronomy Picture of the Day

Invisible AstronomyEarth’s Atmosphere absorbs much of

EM spectrumVisible, some Infrared, Radio make it

throughGet above atmosphere

SummaryTelescopes are “light buckets”3 important jobs2 basic types Invisible Astronomy provides much

more information