new improved eyes telescopes and “invisible” astronomy
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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
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