Electromagnetic radiation

Electromagnetic radiation are composed of photons, linked waves of electric and magnetic fields. These include, radio waves, heat waves (infrared), visible light, x-rays, etc.

A list of the electromagnetic spectrum (note that these boundaries are approximate, they blend into each other):

• Radio waves. ....... 10 cm to 1 km or longer.
• Micro waves. ....... 1 mm to 10 cm.
• Infrared light. ...... 700 nanometers to 1mm. Around 750 to 1,000 nanometers these waves are thermal IR.
• Visible light. ....... 400 nanometers for blue light, to 700 nm for red light.
• Ultraviolet light..... 700 nm to 10 nm. UV light can damage surface tissue, and has sterilized the surface of Mars.
• X-rays. ................ 1 Angstrom to 0.1 Angstrom. These rays can damage deep tissue. (Note 1 Angstrom = 10 nm.)
• Gamma-rays. ...... 0.1 Angstrom and shorter. These can damage deep tissue and can penetrate deep thru many materials.

The lowest energy waves are radio waves. They act like waves. As the energy increases, the wave length shortens, and the photons act more and more like powerful particles that can damage tissue and penetrate deep thru materials.

Light levels on Mars

Mars gets a little less than half the light from the Sun, as Earth. (Mars is 1.524 AU from the sun. Solar Flux at Mars = 1 / (1.524 * 1.524) = 0.4306 or 43% of the light from the sun as Earth.)

This is enough to grow crops, and our eyes (which adapt wonderfully to varying light levels) won't perceive Mars as dim.

Danger of ultraviolet light

Ultraviolet light (UV light) is light with enough energy to damage cells. Life has adapted to somewhat resist this, but on Earth, the largest protection is by the free Oxygen in our atmosphere. UV light will break apart O2, which then combines into O3 or Ozone. Ozone STRONGLY absorbed UV light, so little reaches the surface of Earth. Thus, life is largely protected by the ozone layer in the upper atmosphere.

Mars has only trace amounts of O2 and O3 in its atmosphere, and about 99% of the UV light reaches the Martian surface. This has sterilized the Martian surface (tho life may exist underground). UV light can cause sunburn in humans, cause cataracts in eyes, and make plastics brittle. Thus Martian space suits must be constructed with this danger in mind.

UV light is absorbed by glass, so thick window panes on Mars will block most of the light going thru windows. Windows could be constructed with materials which more strongly absorb UV light, and this should be considered when constructing Martian glass.

However, Mars is so far away from the sun, that it only gets 43% of the UV light that Earth gets, so the problems of UV are mitigated by about half.