How big is X-Ray Wavelength? | Scale of the Universe

X-rays are a form of light that eyes cannot see, with much more energy and much shorter wavelengths than visible light. The explorer shows an X-ray with a wavelength of 0.5 nanometers (500 picometers), well inside the X-ray range. A wavelength is the distance from one crest of a wave to the next, and a nanometer is a billionth of a meter.

Wavelength

NASA gives X-ray wavelengths as between 0.03 and 3 nanometers. At the long end, X-rays border on ultraviolet light. At the short end, they border on gamma rays.

Sources draw these edges in different places. Another NASA page defines X-rays by energy instead, which works out to wavelengths of about 0.012–12 nanometers. The explorer's 0.5 nanometers falls inside both ranges.

Scientists usually describe X-rays by their energy rather than their wavelength, partly because the wavelengths are so small. Light travels in tiny packets of energy called photons. The shorter the wavelength, the more energy each photon carries. X-rays can pass through many materials that absorb visible light.

Size comparisons

A wavelength of 0.5 nanometers is about the width of a cesium atom, one of the largest atoms.
Violet light, the visible light with the shortest wavelength eyes can see, has a wavelength of about 400 nanometers, 800 times as long.
About 160,000–200,000 of these wavelengths would span a human hair, which is 0.08–0.1 millimeters wide.
Each photon of this X-ray carries 1,000 times the energy of a photon of visible light with a wavelength of 500 nanometers.

How X-rays were discovered

Wilhelm Röntgen discovered X-rays in 1895. He was passing electricity through a glass tube of thin gas, which he had covered. A faint light appeared on a light-sensitive screen nearby, caused by a new kind of radiation that could pass through the cover. Röntgen received the Nobel Prize in Physics in 1901.

Röntgen found that X-rays passing through hands and arms made detailed pictures of the bones inside. Bones are dense and absorb more X-rays than skin does. So on X-ray film, the bones leave shadows while the skin looks almost clear.

How X-rays reveal where atoms sit

Waves passing through small, tightly spaced openings form a pattern called a diffraction pattern. In 1912, Max von Laue suggested that the regular rows of atoms in a crystal would do the same to X-rays. Experiments proved him right and showed that X-rays behave as waves. He received the 1914 Nobel Prize in Physics.

William Bragg and his son Lawrence then worked out how an X-ray's wavelength and angle relate to the spacing between layers of atoms. That made it possible to calculate where the atoms in a crystal sit. The Braggs shared the 1915 Nobel Prize in Physics.

Why X-ray telescopes are in space

Earth's atmosphere absorbs X-rays, so X-ray telescopes have to work above it. X-rays do not bounce off a mirror they hit head-on, so these telescopes use mirrors that the X-rays strike at a shallow angle. NASA's Chandra X-ray Observatory detects wavelengths of about 0.12–12 nanometers, which includes 0.5 nanometers. In space, X-rays come from objects millions of degrees hot, such as the disks of gas around black holes.