Reference table
Electromagnetic spectrum
A comparison of electromagnetic radiation by wavelength, frequency, physical scale, and atmospheric transmission.
The boundaries between regions of the electromagnetic spectrum are approximate and vary slightly between fields. Frequency and wavelength are related by f = c / λ.
| Radiation type | Wavelength (m) | Frequency range (Hz) | Scale of wavelength | Penetrates Earth’s atmosphere | Comments |
|---|---|---|---|---|---|
| Radio | > 10⁰ | < 3 × 10⁸ | Buildings to many kilometres | Partially; frequencies above the ionospheric cutoff pass through | Much of the commonly observed radio range reaches the ground, but the ionosphere blocks or reflects the lowest frequencies. The cutoff varies with ionospheric conditions. |
| Microwave | 10⁰ to 10⁻³ | 3 × 10⁸ to 3 × 10¹¹ | A person to a grain of sand | Partially, through atmospheric windows | Water vapour and oxygen absorb particular bands. Wi-Fi/IEEE 802.11 uses several comparatively narrow, region-dependent bands within this region, ranging from sub-1 GHz to approximately 60 GHz. |
| Infrared | 10⁻³ to 7 × 10⁻⁷ | 3 × 10¹¹ to 4.3 × 10¹⁴ | A grain of sand to smaller than a bacterium | Partially, through atmospheric windows | Water vapour, carbon dioxide, and other gases absorb large portions of the infrared spectrum. Some observations require dry, high-altitude, airborne, or space-based instruments. |
| Visible | 7 × 10⁻⁷ to 4 × 10⁻⁷ | 4.3 × 10¹⁴ to 7.5 × 10¹⁴ | Roughly one hundredth the width of a human hair | Mostly | The atmosphere is broadly transparent to visible light, although clouds, aerosols, and gases scatter or absorb some light. |
| Ultraviolet | 4 × 10⁻⁷ to 10⁻⁸ | 7.5 × 10¹⁴ to 3 × 10¹⁶ | Large molecules and viruses | Partially | Most UVA and some UVB reach the surface; UVC and much of UVB are absorbed, predominantly by oxygen and ozone. |
| X-ray | 10⁻⁸ to 10⁻¹¹ | 3 × 10¹⁶ to 3 × 10¹⁹ | Molecules to atoms | No | Earth’s atmosphere absorbs astronomical X-rays, so observations generally require instruments above the atmosphere. |
| Gamma ray | < 10⁻¹¹ | > 3 × 10¹⁹ | Atomic nuclei and smaller | No | Gamma rays interact high in the atmosphere; astronomical observations generally require space-based instruments or detection of secondary particles at the surface. |
“Penetrates” describes transmission to ground level. It does not imply that every frequency in a region is transmitted equally, nor that transmitted frequencies are necessarily practical for communication or ground-based observation.