The Sun does not emit only visible light. It also emits radio, infrared, UV, X and gamma waves.
- Electromagnetic radiation propagates with a velocity c= 299790 km/s.
- 8 minutes and 22 seconds are necessary for light to travel from the surface of the Sun to the Earth.
Parts of the radiation are absorbed by the atmosphere and do not reach the ground. To observe the sky in these wavelengths, we must send receivers into space.
The quantities which define this light are :
- The frequency, f, is the number of pulses per second (hertz is the frequency unit)
- The period, , is the length of one pulse (in seconds)
- The wavelength (the unit is the meter)
- The energy (the unit is the Joule)
h is the Planck constant : h =