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Light, Mirrors and
Telescopes
Rajesh Gupta
University of California, San Diego.
Mr. Smith’s Class
We see things because they
reflect light into our eyes:
Homework
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We hear things when they
vibrate
If something vibrates with a very quickly we say it has a
_____ pitch.
If something vibrates with a vibrates slowly we say it has a
____ pitch.
Words – low, high
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How do we see things?
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Indoors and outdoors
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We make or see or hear waves
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Drawing sounds…
This sound wave has a
_____ frequency:
This sound wave has a
___ _frequency:
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Waves can be small or large
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Waves can be slow or fast
Light travels VERY FAST – around
300,000 kilometres per second.
At this speed it can
go around the world 8
times in one second.
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Small wave to see small things
 But we can use big waves to see large
things
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The Universe is a VERY Big Place
 1,000,000,000,000 galaxies
 100,000,000,000 - 1,000,000,000,000
stars in a galaxy
 About 100,000,000,000,000,000,000,000
kilometers

Light takes 13 billion years to travel
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We can use different waves to
see the universe
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We can use different waves to
see the universe
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We can use different waves to
see the universe
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We can use different waves to
see the universe
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We can use different waves to
see the universe
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We can use light
Light travels in straight lines:
Laser
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Light reflects
Reflected ray
Incident ray
Mirror
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Using mirrors
Two examples:
2) A car headlight
1) A periscope
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Clear vs. Diffuse Reflection
Smooth, shiny surfaces
have a clear reflection:
Rough, dull surfaces have
a diffuse reflection.
Diffuse reflection is when
light is scattered in
different directions
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Mirrors can be concave or
convex
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Convex Mirrors
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Concave Mirrors
Where have you seen it?
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Concave Mirrors and Far
Objects
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Refraction is bending of light
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Lenses use refraction to form
images
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Telescopes and Microscopes
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Telescopes
 Optical Telescopes use light to see
things
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Reflecting telescopes use mirrors
Refraction telescopes use lenses
 Bigger telescopes collect more light
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See more things, see farther
If you double the area of the mirror,
you collect four times as much light
 Radio Telescopes use radio waves
to see things
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Can observe at night, through clouds,
rains
Larger waves, so telescopes can be
bigger
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Refractors (lens based) are
hard to make very large
Yerkes Observatory
40 Inch refractor (1897)
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Reflecting Telescopes
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Observatories
• 100 in. (2.5 m) Hooker,
Mount Wilson. Largest
1917-1948. (photo: Mount Wilson)
• 200 in. (5 m) Hale,
Mount Palomar. Largest
1948-1974. (photo: Alain Maury)
• BTA-6 (6 m), Mount
Pashtoukov. Largest 19741993. (photo: SAO-RAS)
• Keck I & II (9.8 m), Mauna
Kea. Largest 1993(photo: WM Keck Observatory)
Observatories
 Most are made in
high locations and
dry areas

Kitt Peak (Arizona),
Mauna Kea (Hawaii),
Andes Mnts (Chile)
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Kitt Peak Observatories
24 Telescopes
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CTIO (Chile) above
Siding Springs (Australia)
right
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Mauna Kea Observatories 12 telescopes of various sizes
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The Keck Telescopes
Each is 10 meters across
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Subaru Telescope - 8.3 meters
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The Very Large
Telescope
(VLT)
4 telescopes each with
8 m mirrors - acts like
a 16 m telescope
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The Overwhelmingly
Large Telescope OWL
100 meters across
Is there no limit?!?!?!?!?
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Using Other Waves
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Radio Telescopes - Use same
design as visible light
telescope - a parabolic
surface
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Arecibo Radio Telescope
Largest Single Dish
305 m across
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Radio Telescope: Arcibo,
Puerto Rico
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The Very Large Array
27 Radio telescopes acting as
one
Radio Image
of a Supernova
remnant
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Radio Telescopes: Green Bank,
West Virginia
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Ooty Radio Telescope
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GMRT: Giant Metrewave
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Space Telescopes
X-Ray
Chandra Telescope
Infrared
Spitzer Space Telescope
Visible - Ultraviolet
Hubble Space Telescope
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Hubble Space Telescope
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Acknowledgements

Material collected from diverse and many sources, including
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http://observe.phy.sfasu.edu/courses/phy410/lectures410/Movies/sound/
http://science.howstuffworks.com/light14.htm
http://www.kidskonnect.com/LightSound/LightSoundHome.html
The Soundry: How We Perceive Sound: The Ear
The Science Spot: Physics - Light & Sound
What are waves?, NASA
Physics Zone: Lessons on Waves, Light, and Sound
http://www2.biglobe.ne.jp/~norimari/science/JavaEd/e-wave6.html
Waves, Light and Sound Review
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http://www.glenbrook.k12.il.us/gbssci/phys/reviews/63reviews/u11and12/u1112rev.html
http://online.physics.uiuc.edu/courses/phys150/fall03/slides/lect11.pdf
P100_Class10_ICQ.pdf (application/pdf Object)
http://www.astro.ubc.ca/people/newbury/astro311/notes/060925h.pdf
Waves&Superposition.pdf (application/pdf Object)
http://www.ifa.hawaii.edu/~stalder/astro110/lectures/lecture9.pdf
http://www.colloid.nl/Education/Nat1chem/waves-lectures-Nat-Chem-2006.pdf
The educational encyclopedia, physics, optics and color
The Physics Classroom
http://faculty.salisbury.edu/~jwhoward/astro108/html/present.htm
Giant Meterwave Radio Telescope; Ooty Radio Telescope
http://www.ece.vt.edu/swe/RFI2004/35.pdf
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