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PROPERTIES OF LIGHT, TELESCOPES AND OBSERVING TECHNIQUES
Pre-lab Review
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?
Light (of course!) But what else and how? Any 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
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
Wave-Particle Duality Pt. 1Wave-Particle Duality Pt. 2
Electromagnetic Spectrum
Constellation Map
Observing Techniques: EM Spectrum
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 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
Mounts Equatorial (use RA and Dec as coordinates) Dobsonian (use altitude and azimuth as
coordinates) 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
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
There are many things we need to consider when observing Earth’s daily motion Earth’s yearly motion Location
Earth’s atmosphere (H20, O2) absorbs incoming light at certain wavelengths Put telescopes at high altitudes or in deserts to
minimize atmospheric absorption To avoid atmosphere and light pollution
completely, move to space Putting telescopes in space is VERY expensive!
This lab…
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
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