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1 Apr 2012
Astronomy Chapter 1 Notes
The Scientific Method
- The Scientific Method: a way of trying to make sense of the universe
1) Observation: observe and try to understand
2) Hypothesis: make an educated guess
3) Experiment: set up an experiment
4) Conclusion: draw a conclusion on previous hypothesis
5) Next step is that someone else has to do it. it has to be reproducible from an
independent researcher
Electromagnetic Spectrum
- Astronomical information is transmitted by electromagnetic waves or starlight
- Astronomy is the only field you cannot take into the laboratory. You can only observe
and extract all possible information.
- Starlight: tells us temperature, chemical composition, motion, pressure, magnetic fields
- EM Spectrum:
- Light: mutually perpendicular oscillating electric and magnetic fields
- Light moves in a wavelike pattern at a speed of c = 3 X 10 m/s (c=speed of light)
- Theory of relativity says nothing with mass can go as fast as the speed of light
- Wavelength : distance between peaks of waves (important because it determines
- Tachyons: theoretical faster-than-light particles
- EM Spectrum: 1 X 10
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- Default of lambda is wavelength of light
- E=mc E=energy m=mass c=speed of light
- There is a debate whether light is a little photon (a burst of energy) or a wave
- When testing whether light behaves like a wave or a particle, it behaves according to the
test you set out for it, i.e. testing if it behaves like wave it behaves like a wave and vice-
versa. Proven in the young or photoelectric test. Wave/light duality
- Photoelectric theory shows how light behaves/moves like a particle
- Magnetic and electric fields are perpendicular to one another, and velocity of light is
perpendicular to the field
- Light gives us colour
- The colour blue indicates a short wavelength while the colour red indicates a long
wavelength. In fact it is almost twice as long as blue
- To measure the wavelength of visible light the metre stick is too big. It must be measured
in nanometres which is a billionth of a metre stick
- Shorter than 400nm is ultra violet light and is extremely dangerous to your vision
- **Visible Colours: ROY G BIV (I stands for indigo)
- On test you must know the wavelength of red, violet, and green. They are 700, 400, and
550 respectively
- Photons: bundles of energy light as a particle
- With white light (mixture of all colours) each wavelength gets bent at a different angle
and white light is disbursed into different colours
- Wavelengths that are shorter than ultraviolet rays (400) are x-rays and gamma rays.
Gamma rays come from nuclear reactions
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Shortest wavelengths to longest:
1) Gamma Rays
2) X-rays
3) Ultraviolet
4) Visible colours ROY G BIV
Wavelengths longer than red
5) Infrared (cannot see but you can detect from heat)
6) Radio Wavelengths
- Frequency = f = number of wave peaks passing a given point each second
- How many times something happens over a time unit
- Frequency is measured in waves/second = complete cycles/second = cycles/second = Hz.
Named Hertz in his honour
- **POSSIBLE TEST QUESTION: What is the frequency of green light? Speed of
- The shorter the wavelength the higher the frequency
Planck Curve
- Get star in telescope
- Put a sequence of coloured filters at the eyepiece end of a telescope
- Starlight passes through a filter and then to a computer
- Computer gives numerical value for light intensity passing through each coloured filter
- Plot of wavelengths of colour against the intensity or #of photons each second
- A Blackbody is a theoretical object that absorbs all wavelengths
- If a Blackbody is heated it will glow and emit wavelengths of whatever colour it is heated
to (a.k.a its temperature). The Planck Blackbody curve is an indication of temperature
- It will always be a curve because one of the colours will emit the most light
- Planck blackbody curve tells us the temperature of a star on the surface
- Planck curve is a graph of filter colour (=wavelength) vs. intensity (THIS WAS AKSED
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