Electromagnetic radiation (EMR) provides all our information about the physical Universe, apart from meteorites and lunar rock samples. Visible light is just one form of this radiation.
If you think of EMR as energy conveyed in the form of a wave motion. As can be derived from the name, physicists recognise two components to EM waves: electrical & magnetic, and the electrical and magnetic fields oscillate at right angles to one another. EMR can also be thought of as a stream of massless particles called photons. In certain circumstances it is more convenient to describe EMR in terms of a wave and in others as a stream of particles.
Different colours of light, (radio waves etc.) are characterised by their own wavelengths. The complete range of wavelengths form the electromagnetic spectrum. All EMRs travel through a vacuum in a straight line at 3 × 108 ᵐ⁄s.
As the radiation's wavelength decreases, so its photons become more energetic & penetrating. Planck's law describes this:
E = ʰᶜ⁄λ
where E = energy of the photon, h = Planck's constant ( = 6.63 × 10⁻³⁴ Js (Joule-second), c = speed of light, and λ = wavelength of radiation in metres.
Most of the incoming EMR from space is absorbed by the Earth's atmosphere, except for some wavelengths such as those in the visible spectrum.
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