Optical Telescopes Ground based and on satellites Observations are recorded using a camera instead of the human eye most times This is so we can separate colors into light and using times to study changes over time ID: 420546
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TelescopesSlide2
Optical Telescopes
Ground based and on satellites
Observations are recorded using a camera instead of the human eye most times.
This is so we can separate colors into light and using times to study changes over time.All optical telescopes are reflecting telescopes.Mirrors are perfectly shaped and made of high quality, clear glass.Mirrors are mounted at the bottom of the scope for stabilityMirrors do not produce chromatic aberration.Lens brings different colors of light into focus at different places.Telescopes are like a giant eye.They collect more light than our eyes allowing us to see faint objects in greater detail.Slide3
Two major properties of Optical telescopes
Light collection area: how much light the telescope can collect at one time.
The bigger the area, the more light collection.
Angular resolution: the smallest angle over which we can tell two stars are distinct.Large telescopes can have large angular resolution but is limited due to Earth’s atmosphere.Diffraction Limit: an interference of lightDepends on the diameter of the telescope mirror and wavelength being observedLarge telescopes have small diffraction limit and better (smaller) angular resolutionSlide4
Ground based telescopes
Pro: Less expensive to build, operate, and maintain
Con: daylight and weather
Can observe Radio Waves, Microwaves, Visible light, and parts of Infrared Slide5
Problems from our atmosphere
Light pollution
Twinkling/atmospheric turbulence
Wind and air currents are constantly moving around.Changes atmosphere’s light bending properties, or view of things outside Earth’s atmosphere appear to jiggle aroundBlurs astronomical imagesMost forms of light do not reach the ground.Slide6
Space based telescopes
Pro: above the atmosphere, unaffected by daylight and weather, light pollution, and atmospheric turbulence.
Con: More expensive and time consuming to build and maintain
Can record microwaves, infrared, visible light, ultraviolet, x-rays, and gamma raysSlide7
Types of Telescopes
Refracting Telescope
Reflecting Telescope
Multiple-Mirror Reflectors (MMT)Schmidt TelescopeSlide8
Refracting Telescope
Developed by Galileo
Very simple, but expensive
Uses Objective lens to bend light to a focus pointLight passes through a lens having an inverted imageFocal length: the distance from the lens to where the focus will occur. Variables that change this are thickness and curvature.Increase both = decrease focal lengthDecrease both = increase focal lengthDisadvantage: two focal points creates chromatic aberration.Slide9Slide10
Reflecting Telescope
Developed by Newton
Use of concave mirror to reflect light to one point
Very cheapLight is collected by concave mirror produces small imageSecond mirror reflects the image to the eyepiece where it is magnifiedNo chromatic aberrationExample Hubble Space TelescopeSlide11
Hubble Space Telescope
Named after Edwin Hubble
First launch on April 24, 1990
Job: discover all forms of light in the electromagnetic spectrumProblem 1: mirror couldn’t focus, had a spherical aberration because it was too flat and didn’t account for zero gravityProblem 2:pin used for stability was put in backwards, NASA knew about it and ignored it. Made things off by one human hair = 1 micron.Now 100% functionalAdvantage = easy to work onTypical maintenance: replace solar units and fuses, and correct optics on cameras.Slide12Slide13
Radio Telescopes
Most common type in the world
Similar to a satellite dish
Differences: they look into the sky, larger in size, different purpose.Pointed towards cosmic sources that rise and set with Earth’s rotation.Atmosphere does not distort radio waves like it does with visible light.No advantage to observe from space.Dish reflects radio waves to an antenna which takes the signal and amplifies it and then records it. Recorded on paper and makes a contour map.Slide14
Interferometry
Allows multiple radio telescopes to be linked in a way that allows them to obtain the angular resolution of a much larger telescope.
Example: VLA – Very Large Array (in NM)
27 radio telescopesSlide15
Other Telescopes
Multiple-Mirror Reflectors (MMT)
Several mirror take the place of a single large mirror
Less expensive to build than a single large mirror.Schmidt TelescopeUses both reflecting mirror and refracting lensUsed to make wide-angle photographs of the sky