The electromagnetic spectrum is one family of waves: electric and magnetic fields rippling through spacetime, carrying energy. Radio, microwaves, infrared, light, UV, x-rays and gamma rays are all the same phenomenon. This view spans all known types of electromagnetic radiation, sixteen orders of magnitude, from radio waves that pass through you unfelt to gamma rays that can snap your molecules apart and, at the intensity of a nuclear fireball, vaporize you outright. Below, explore. Choose two signals. Compare their frequency, wavelength, photon energy, and how matter responds.
Wavelength, for scale
This view spans 10 kHz to 100 EHz, sixteen orders of magnitude of one phenomenon, not the physical beginning or end of the spectrum. Click a region to focus on it, or drag the bright window.
Click moves the marker · drag a handle · scroll or pinch to zoom · double-click a landmark to center it.
| Relationship (B vs A) |
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photon energy E = hν (h = 6.626×10⁻³⁴ J·s) beam power P = photons per second × energy per photon
Frequency fixes the energy of each photon. It does not fix how many photons a source emits; that is power, and power belongs to the source, not to the spectrum.
These regimes overlap and depend on the material; they are common mechanisms, not walls. The named spectrum bands themselves are conventions with soft edges, not laws of nature.
The width of the box is the window you picked, so the number of cycles drawn is literally frequency times window. Only the animation speed is compressed: nothing can be shown moving at 1023 cycles a second. A wave too dense to resolve dissolves into a smear, which is the honest picture, because too fast to see is a blur rather than a strobe. Pick a shorter window and the fast lane slows into a wave while the slow lane flattens to a line.
Different animals are issued different slices. Bees and birds see into the ultraviolet; pit vipers image the world in the infrared glow of their prey; your own skin senses radiant warmth far below what your eyes catch. And one correction to a common mix-up: no ear hears radio. Sound is pressure waves in air, not electromagnetic radiation: different physics that borrowed the same vocabulary. Meet the whole spectral zoo →
Roughly what a clear sky at sea level lets down to the ground. Two doors are open: the radio window (the ionosphere turns back anything below about 10 MHz, and water vapour and oxygen close it again past about 30 GHz), and the optical window with a few infrared side doors between the water-vapour bands. Ozone shuts the door at 300 nm, and from there up the air itself absorbs everything: ultraviolet, X-rays and gamma rays are astronomy from orbit. Above about 100 GeV the gamma rays come back into reach from the ground, caught by the blue Cherenkov flash they make in the air. A dry mountaintop opens the millimetre and infrared cracks wider, which is why those telescopes live on Mauna Kea and the Chajnantor plateau, and why the infrared one that matters most went to space.
Redshift is not a colour filter. Space itself has expanded while the light was in transit, and every wave in it stretched by the same factor, 1 + z, so a line emitted at one wavelength arrives at that wavelength times 1 + z, and its frequency and photon energy fall by the same factor. The lookback times come from the standard cosmology (flat, H₀ = 67.7 km/s/Mpc, Ωm = 0.31), which puts the universe at 13.8 billion years old.
Everything above, from the slowest radio rumble to the fiercest gamma ray, fits in a window of about 53 octaves of frequency. That is the entire observed electromagnetic range.
An octave is one doubling. The word is borrowed from music: the A above middle C vibrates 440 times a second, and the next A up, at 880, is the same note one octave higher. Frequency works the same way everywhere, so the natural unit of the spectrum is not "plus so many hertz" but "doubled so many times". Radio to gamma is 53 doublings, stacked.
Doubling hides its own size. To feel it, take one walking step, 0.75 m, and double it once per octave. The named bands are marked at the octave where each begins:
One step becomes seven-tenths of a light-year, most of the way through the comet halo at the solar system's edge, a sixth of the distance to the nearest star. Radio to gamma is the gap between a footstep and the Oort cloud, and the entire visible rainbow is a single stride somewhere along the way.
You are reading this page by catching a hail of half-quadrillion-hertz photons that left a glowing rectangle nanoseconds ago, light your eyes were built for. Of the fifty-three octaves above, you were issued one. Spend it well.