The Nature of Light
- As opposed to other scientists, Astronomers generally cannot
conduct "hands-on" experiments. They primarily collect and
analyze light from distant inaccessible objects.
- Light carries information about
- A source of light produces photons - small
packages of energy which leave the source and travel through space (or any
transparent material) at the speed of light - 300,000 km/s.
- Photons have a wave nature. Each one is a small packet of waves.
- Waves have a well-defined wavelength, - the distance between wave crests.
- Wave crests pass by a fixed point at a measureable rate - crests per second - the frequency - ν.
- For any wave
Wavelength x Frequency = Speed of Propagation
- Ocean waves travel in water. Sound waves travel in air...
- Different types of light (e.g. Radio, Infrared, Visible...) are
distinguished by their wavelength, as are different colors of
light in the visible part of the electromagnetic spectrum.
- Within the visible portion of the spectrum our eyes
sense different wavelengths of light as different colors.
- "White" is our brain's response to our eyes receiving all colors
at the same time.
- The principal regions of the electromagnetic spectrum (from long wavelengths to short) are Radio, Infrared, Visible, Ultraviolet, X-ray, and Gamma-ray
- Each photon carries a discrete amount of energy which depends
upon its wavelength.
- Energy, wavelength, and thus color, are all equivalent.
- h is just a constant of nature -- Planck's constant. The
value is not important here.
- c is a constant as well -- the speed of light. Its numerical value (3x108 meters/sec) is not important
to understanding this equation (but it is a value you need to know).
- What IS important is that this equation says that short wavelength photons (e.g. X-rays and -rays) carry
much more energy per photon than photons that have a long wavelength
(e.g. radio or infrared light).
- Light sorted according to wavelength produces a spectrum.
Revised October 2, 2003