50 Fun Facts About Electromagnetic Spectrum

Percy Spencer, whose candy bar reportedly melted beside a radar set, first deliberately microwaved which food?

Popcorn was the first food Spencer cooked on purpose; the second was an egg, which exploded in the face of a fellow experimenter.

The first X-ray photograph of a human body, taken in December 1895, showed which part of the physicist's wife?

Her hand was the subject, and on seeing her own skeleton Anna Bertha is said to have exclaimed, "I have seen my death!"

Which nutrient, needed for strong bones, does human skin make when ultraviolet B rays in sunlight strike it?

Vitamin D forms when UVB strikes a cholesterol-like compound in the skin, and because window glass blocks almost all UVB, sunshine through a window does not do the job.

Which space telescope, launched on Christmas Day 2021, has a gold-coated mirror built to observe infrared light?

James Webb carries 18 hexagonal mirror segments plated in gold, a metal chosen because it reflects infrared light so well.

Which short-range radio technology is named after a tenth-century king who united Denmark's tribes?

Bluetooth takes its name from King Harald Bluetooth, and its logo is a bind rune that merges the runes for his two initials.

Which everyday household gadget sends its commands as coded pulses of invisible infrared light?

TV remote control signals are invisible to the eye, yet a phone camera pointed at the handset will often show them flashing.

Which gas high in Earth's atmosphere absorbs most of the Sun's harmful ultraviolet radiation?

Ozone in this layer soaks up 97 to 99 percent of the Sun's medium-frequency ultraviolet light, which would otherwise damage life at the surface.

Photo 51, an X-ray image taken under Rosalind Franklin's supervision in 1952, revealed the structure of which molecule?

DNA was the molecule, and the photo, the 51st in its series, was shown to rival researcher Watson without Franklin's permission.

From the 1920s, which kind of shop let customers view their own bones through an X-ray machine?

Shoe shops used the fluoroscope so parents could watch a child's toes wiggle inside a new pair, but tests in 1948 found the machines poor at fitting.

Which home wireless technology shares the 2.4 GHz band with microwave ovens and may slow when one is running?

Wi-Fi can stutter because the ovens cook at about 2.45 GHz, and the small amount of radiation that escapes lands on the same waveband.

Which astronomer, the discoverer of Uranus, found infrared in 1800 with a thermometer placed just beyond red sunlight?

William Herschel called his find "calorific rays", and his studies led to the finding that slightly more than half of the Sun's energy reaching Earth is infrared.

Which German physicist won the very first Nobel Prize in Physics, in 1901, for discovering X-rays?

Wilhelm Röntgen refused to patent the discovery so that society as a whole could benefit, and he was so shy of public speaking that he declined to give a Nobel lecture.

Which German physicist, whose name is now the unit of frequency, first produced radio waves in the 1880s?

Heinrich Hertz did not realize the practical importance of what he had done, reportedly calling the experiment "of no use whatsoever" beyond proving a theory right.

Which Scottish physicist showed in the 1860s that light is a wave of electric and magnetic fields?

James Clerk Maxwell found that electric and magnetic fields travel together as waves at the speed of light; Einstein called his work the most profound since Newton.

Radio waves and gamma rays cross empty space at the same speed, roughly how many kilometres per second?

300,000 kilometres per second, or about a billion kilometres per hour, is the one speed that every kind of electromagnetic wave shares in a vacuum.

Which glass object did Isaac Newton use in the 1660s to split a beam of sunlight into a band of colours?

A prism did the splitting, and Newton, who named the resulting band a spectrum, then used a lens and a second one to blend the colours back into white light.

Which process warms Earth as gases such as carbon dioxide absorb infrared radiation rising from the ground?

The greenhouse effect works because the atmosphere absorbs about 90% of the longwave radiation the surface gives off but only 23% of incoming sunlight.

Which pigment does human skin make more of after exposure to ultraviolet rays, producing a suntan?

Melanin acts as a built-in sunscreen: its dark form, eumelanin, can dissipate more than 99.9% of the UV radiation it absorbs.

Which hospital machine builds images from pulses of radio waves inside a strong magnet, with no X-rays involved?

An MRI scanner spares the patient the radiation dose of CT and PET scans; the trade-off is a longer, louder stay inside a confining tube.

Which scientist equipped a fleet of mobile X-ray vans for French field hospitals during World War I?

Marie Curie's vans became known as petites Curies, or "Little Curies", and her X-ray units are estimated to have treated over a million wounded soldiers.

Which leftover glow of the Big Bang did Penzias and Wilson first suspect was pigeon droppings fouling their antenna?

The cosmic microwave background hiss stayed put after the birds were evicted and the antenna scrubbed, and the accidental find won the 1978 Nobel Prize in Physics.

Which spinning stars, found by Jocelyn Bell in 1967, sent radio blips so regular they were nicknamed "Little Green Men"?

Pulsars tick so steadily, the first one every 1.337 seconds, that Bell's supervisor at first dismissed the signal as radio interference.

US Vela satellites, built to catch secret Soviet nuclear tests, instead discovered which cosmic explosions in 1967?

Gamma-ray bursts first showed up on 2 July 1967 as a flash unlike any known weapon signature, and the discovery was not published until 1973.

What do astronomers call the stretching of light from distant galaxies to longer wavelengths as the universe expands?

Redshift readings let Edwin Hubble report in 1929 that the more distant a galaxy is, the more its light is stretched, a rule now called Hubble's law.

Which element was first detected as a yellow line in sunlight during an 1868 eclipse, before being found on Earth?

Helium takes its name from helios, the Greek word for the Sun, because Norman Lockyer argued the line came from a new element; chemists only isolated it in 1895.

Radio astronomy began in the 1930s when Bell Labs engineer Karl Jansky traced a faint hiss of static to which source?

The Milky Way was the source, strongest toward the constellation Sagittarius; Jansky had only been asked to hunt down static that might spoil radio telephone calls.

Which planet-wide network of radio dishes produced the first image of a black hole in 2019?

The Event Horizon Telescope links radio dishes around the globe into a single array, and its first picture showed the black hole at the centre of the galaxy Messier 87.

Which colour do the very hottest stars shine, with surfaces several times hotter than the Sun's?

Blue stars of spectral class O have surfaces of 30,000 kelvin or more and pour out so much ultraviolet that they look bluish-white to the eye.

Which NASA telescope, carried up by Space Shuttle Columbia in 1999, studies black holes and exploded stars in X-rays?

Chandra honours the astrophysicist Subrahmanyan Chandrasekhar, and the name also happens to mean "moon" in Sanskrit.

Which X-ray source, the first widely accepted black hole, did Stephen Hawking and Kip Thorne famously bet on?

Cygnus X-1 was found in 1964 by instruments on a sounding rocket, and Hawking, who bet against a black hole while hoping to lose, conceded in 1990.

At night, AM radio signals travel far beyond their daytime range by bouncing off which layer of the atmosphere?

The ionosphere is an electrically charged layer of the upper atmosphere that bends the signals back toward the ground, a trick radio amateurs have exploited since the early 1920s.

Which Italian inventor reported receiving the first radio signal sent across the Atlantic Ocean, in 1901?

Guglielmo Marconi listened in Newfoundland, with an antenna held up by a kite, for the Morse code letter S tapped out again and again from Cornwall.

What name is given to the coloured glow many substances give off under a black light as they absorb ultraviolet?

Fluorescence stops almost the instant the lamp is switched off, which is what separates it from the lingering glow of phosphorescence.

Tonic water glows under an ultraviolet lamp because it contains which bitter compound, once taken against malaria?

Quinine was mixed with soda and sugar in British India to mask its bitter taste, which is how the drink was born; gin went in later for the same reason.

A 2011 London study found which Arctic animals can see ultraviolet light, making fur and urine stand out sharply?

Reindeer can see wavelengths as short as 320 nanometres, well below the human limit of about 400, which may also help them pick out lichen to eat against the snow.

Before some X-ray exams, patients swallow a chalky white "meal" containing a compound of which metal?

Barium sulfate does not let X-rays pass, so the parts of the digestive tract it coats show up clearly white on the image.

The microwaves that heat food inside a kitchen microwave oven have a wavelength of roughly what size?

About 12 centimetres is far wider than the holes in the door's metal mesh, so the microwaves stay in while visible light slips out and lets the cook watch.

Which radar tube, greatly improved at the University of Birmingham in 1940, now generates the waves in microwave ovens?

The magnetron, a device the size of a small book, shrank radar sets enough to fit inside fighter aircraft and gave the Allies a lead their enemies never closed.

In 1967 the second was redefined by a microwave frequency given off by atoms of which metal?

Caesium-133 atoms supply the tick: one second is exactly 9,192,631,770 cycles of the radiation from a single transition inside the atom.

A NASA spacecraft discovered in 1994 that millisecond flashes of gamma rays come from which everyday weather events?

Thunderstorms give off these terrestrial gamma-ray flashes, nicknamed dark lightning, in pulses that last between 0.2 and 3.5 milliseconds.

What name is given to a single particle of electromagnetic radiation, whether it belongs to a radio wave or a gamma ray?

Photon comes from the Greek word for light, and every one of these massless particles moves at the same speed through a vacuum.

Gamma rays, X-rays and the highest-energy ultraviolet can knock electrons off atoms, which earns them what label?

Ionizing radiation has no sharp starting line within the ultraviolet, because different atoms and molecules give up their electrons at different energies.

Electromagnetic waves vibrate at right angles to their direction of travel, which makes them what kind of wave?

Transverse waves contrast with longitudinal ones such as sound, whose vibrations run along the line of travel as squeezes and stretches of the air.

Which German physicist launched quantum theory in 1900 by proposing that energy comes in tiny packets called quanta?

Max Planck's law avoided what was later called the "ultraviolet catastrophe", a classical prediction that fails at high frequencies, and his quanta won him the 1918 Nobel Prize in Physics.

Which New Zealand-born physicist named gamma rays in 1903, having already named alpha and beta rays?

Ernest Rutherford ordered the three rays by how deeply they penetrate matter, so gamma, the most penetrating, took the third letter of the Greek alphabet.

Which father and son shared the 1915 Nobel Prize in Physics for using X-rays to work out crystal structures?

The Braggs got there after Lawrence, strolling by a river, realised that X-rays would bounce off the sheets of atoms in a crystal only at certain angles.

Which German physicist discovered ultraviolet in 1801 by watching silver chloride blacken just beyond violet sunlight?

Johann Ritter had gone looking for a cooling counterpart to the heat rays found beyond red a year earlier, and his "chemical rays" were only later renamed.

Which French scientist discovered gamma rays in 1900 while studying the radiation given off by radium?

Paul Villard never gave his rays a name, so it fell to another physicist three years later to recognise them as a distinct type and give them a Greek letter.

Dark lines in the Sun's spectrum, which reveal the elements in its atmosphere, are named after which German physicist?

Joseph von Fraunhofer measured the lines in 1814, and about 45 years later they were matched to the glow of heated elements, revealing what the Sun is made of.

Which American amateur built the first dish-shaped radio telescope in his back yard in Wheaton, Illinois, in 1937?

Grote Reber's nine-metre dish of sheet metal made him, for nearly a decade, the world's only radio astronomer.