Light and Telescopes Chapter 5. Traditional Telescopes The 4-m Mayall Telescope at Kitt Peak...
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Transcript of Light and Telescopes Chapter 5. Traditional Telescopes The 4-m Mayall Telescope at Kitt Peak...
Advances in Modern Telescope Design (I)
Modern computer technology has made possible significant advances in telescope design:
1. Simpler, stronger mountings (“Alt-azimuth mountings”) to be controlled by computers
Advances in Modern Telescope Design (II)
2. Lighter mirrors with lighter support structures, to be controlled dynamically by computers.
Floppy mirror
Segmented mirror
The Keck Telescopes
The two Keck Telescopes on Mauna Kea, Hawaii. Each telescope has a mirror diameter of
10 meters.
Examples of Modern Telescope Design
The Large Binocular Telescope (LBT)
The Very Lage Telescope (VLT) in
Chile
The Future of Optical Telescopes
The European Extremely Large Telescope (E-ELT): 906 segments in a
42-m mirror!
The Giant Magellan Telescope (2016)
Adaptive OpticsComputer-controlled mirror support adjusts the mirror
surface (many times per second) to compensate for distortions by atmospheric turbulence.
Distortions by the atmospheric turbulence are measured using a
laser beam.
InterferometryRecall: Resolving power of a telescope depends on
diameter D:
min = 1.22 /D.
This holds true even if the entire surface is
not filled out.
→ Combine the signals from several
smaller telescopes to simulate one big
mirror → Interferometry
What a telescope does
• Typical resolution of eye is about 0.5 minutes of arc or 30 arc seconds.
• HST has a resolution of 11.6/240 = .048 arc seconds. With HST we can resolve objects that are almost 1000 times smaller.
• NOTE the equation used above was given on page 77 of the textbook.
CCD ImagingCCD = Charge-coupled device
• More sensitive than photographic plates
• Data can be read directly into computer
memory, allowing easy electronic manipulations
False-color image to visualize brightness contours
Negative Images
The galaxy NGC 891 as it would look to our eyes (i.e., in real colors and
brightness)
Negative images (sky = white; stars = black) are
used to enhance contrasts.
The SpectrographUsing a prism (or a grating), light can be
split up into different wavelengths (colors!) to produce a spectrum.
Spectral lines in a spectrum tell us about the chemical
composition and other properties of the observed
object.
Radio TelescopesLarge dish focuses the energy of radio waves onto a small receiver (antenna).
Amplified signals are stored in computers and converted into
images, spectra, etc.
Radio MapsIn radio maps, the intensity of the
radiation is color-coded:
Red = high intensity; Violet = low intensity
Just like optical telescopes, radio telescopes should be built in regions with low average rainfall and cloud cover, and low radio noise.
Radio Interferometry
The Very Large Array (VLA): 27 dishes are combined to simulate a large dish of 36
km in diameter.
Just as for optical telescopes, the
resolving power of a radio telescope is
min = 1.22 /D.
For radio telescopes, this is a big problem: Radio
waves are much longer than visible
light.
→ Use interferometry to
improve resolution!