PROPERTIES OF LIGHT,
TELESCOPES AND OBSERVING
TECHNIQUES
Pre-lab Review
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Wave Properties
 Frequency:
the number of complete waves that pass a
point in one second
 Wavelength: the length of one complete wave cycle
 Amplitude: maximum amount of displacement of a
particle from its rest position
 Period: the time it takes for one complete wave to pass
a given point
What can we observe?
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Light (of course!) But what else and how?
 Any
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ideas??
Cosmic rays and other charged particles
Meteorites
Gravitational waves
These are all often difficult to observe, infrequently
observed or not especially helpful
Since light is the most common and useful
observable, we will focus on light and its various
properties
Wave-Particle Duality
 Light
can be interpreted as both a wave and a particle
 Waves
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Light has a “color” or place on the EM spectrum
(wavelength, frequency)
 Particles
Light consists of particles called photons, as discussed by
Einstein
 Light has “quantized” energy levels, meaning it can only be
at one particular energy level at a time
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Wave-Particle Duality Pt. 1
Wave-Particle Duality Pt. 2
Electromagnetic Spectrum
Constellation Map
Observing Techniques: EM Spectrum
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There are many different techniques for observing
depending on what type (wavelength) of light you
want to observe
 Long
wavelength astronomy: use an array of radio
dishes (interferometry) to collect light
 Visible astronomy: Use telescopes to take images, use
spectrometers that disperse (separate) light to obtain
spectrum and composition
 Short wavelength astronomy: Difficult to observe from
the ground due to the atmosphere, so need to go to
space to observe at these wavelengths
Telescopes: Some Definitions
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Telescopes are made to collect and concentrate
light
Come in two types: refractors and reflectors
Focal Length: distance needed to focus light to a
point
Resolution: how close two objects can be before
they can’t be differentiated
Magnification: ratio of the focal lengths of the
telescope and the eyepiece
 More

zoomed in ≠ better!
Aperture: diameter of primary lens or mirror
Telescopes
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Mounts
 Equatorial
(use RA and Dec as coordinates)
 Dobsonian (use altitude and azimuth as coordinates)
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CCDs
 Like
little photon buckets that convert photons to
electrons
 Basic cameras and cellphones use CCDs!
 Astronomers used to have to draw their observations;
using CCDs is much easier and generally more
accurate!
Telescopes: Refractors
Telescopes: Newtonian Reflectors
Telescopes: Cassegrain Reflectors
Observing Techniques
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Since we will observe in the visible part of the EM
spectrum, from the ground and with small
telescopes, we’ll focus on techniques for observing
under these conditions.
 Star
hopping – “hop” between bright, easily found
objects in the sky to lead to a fainter object that is
difficult to spot
 Using constellations – similar to star hopping
 Using coordinates – useful when doing
astrophotography and using an equatorial mount
 The only way to improve is with practice!
Observing Difficulties
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There are many things we need to consider when
observing
 Earth’s
daily motion
 Earth’s yearly motion
 Location
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Earth’s atmosphere (H20, O2) absorbs incoming light
at certain wavelengths
 Put
telescopes at high altitudes or in deserts to minimize
atmospheric absorption
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To avoid atmosphere and light pollution completely,
move to space
 Putting
telescopes in space is VERY expensive!
This lab…
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Some useful quantities…
 Refractor:
15 foot focal length, 12’’ aperture
 Dobsonian: 1200mm focal length, 8’’ aperture
 Galileoscope focal length: 50 cm, 51 mm aperture
 Magnification = focal length of telescope
focal length of eye piece