Transcript Telescopes

Telescopes
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 stability
– Mirrors 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.
• 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 light
– Depends on the diameter of the telescope mirror and
wavelength being observed
– Large telescopes have small diffraction limit and
better (smaller) angular resolution
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
• 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 around
• Blurs astronomical images
– Most forms of light do not reach the
ground.
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 rays
Types of Telescopes
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Refracting Telescope
Reflecting Telescope
Multiple-Mirror Reflectors (MMT)
Schmidt Telescope
Refracting Telescope
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Developed by Galileo
Very simple, but expensive
Uses Objective lens to bend light to a focus point
Light passes through a lens having an inverted
image
Focal length: the distance from the lens to where
the focus will occur. Variables that change this are
thickness and curvature.
Increase both = decrease focal length
Decrease both = increase focal length
Disadvantage: two focal points creates chromatic
aberration.
Reflecting Telescope
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Developed by Newton
Use of concave mirror to reflect light to one point
Very cheap
Light is collected by concave mirror produces
small image
• Second mirror reflects the image to the eyepiece
where it is magnified
• No chromatic aberration
• Example Hubble Space Telescope
Hubble Space Telescope
• Named after Edwin Hubble
• First launch on April 24, 1990
• Job: discover all forms of light in the electromagnetic
spectrum
• Problem 1: mirror couldn’t focus, had a spherical
aberration because it was too flat and didn’t account
for zero gravity
• Problem 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% functional
• Advantage = easy to work on
• Typical maintenance: replace solar units and fuses, and
correct optics on cameras.
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.
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 telescopes
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 Telescope
– Uses both reflecting mirror and refracting lens
– Used to make wide-angle photographs of the sky