Human ears have two main jobs: alerting us to noises in the world around us, and keeping our bodies balanced as we move throughout the day. However, researchers have found another small trick our ears can perform: determining the temperature of water. While they may look identical, hot and cold water make different sounds when poured. With a little help from our brains — which learn to recognize the contrasting tones over a lifetime of repeated exposure — most people can tell the difference between cold water poured from a pitcher or hot water transferred from a kettle, without even seeing the cup being filled.

Salt makes water boil faster.

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There is truth to this kitchen lore — adding salt makes it harder for water molecules to become steam, creates a higher boiling point, and makes water hotter, faster. But in small amounts, like a teaspoon, salt’s effects are limited, meaning this trick saves just a few seconds of time.

Without the cues of visible boiling or a collection of ice crystals, liquid water tends to look the same regardless of its temperature. What humans can’t see is that temperature actually affects water’s viscosity (aka thickness), which produces different sounds that we can hear. At lower temperatures, water molecules are sluggish and create temporary bonds that thicken the liquid, producing a lower-frequency sound when poured. Conversely, heated water molecules are more energetic, making it harder for molecules to join together. Fewer bonds result in thinner water, which produces a noticeably higher-pitched sound when transferred into a cup. Researchers say bubbling also plays a role in water acoustics — hot liquids have more bubbles than cool liquids, which contribute to the higher tones we hear while pouring out a cup of coffee or tea.

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Stargazers who live in major cities know all about light pollution, but this lack of complete darkness goes beyond geography. It turns out the sky is never totally black no matter where you live, even at night. We can mostly chalk this up to the luminous effects of moonlight and starlight, as well as to our atmosphere, which, in addition to making the planet’s air breathable, scatters all the light that passes through it. (This is what makes the sky appear blue during the day, as the atmosphere scatters blue light more than other colors.)

Water is intrinsically blue.

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Though it appears clear and colorless in small amounts, water naturally has a slight blue color caused by the absorption of light at red wavelengths.

In highly populated areas, the effect of light pollution is known as skyglow, and it’s what gives the night sky its milky, sometimes yellowish complexion. But even if you find yourself in an extremely remote location, the sky would be closer to a navy blue than black. As previously mentioned, this is partially because of the moon, but it’s also because the atmosphere itself emits a faint light of its own (in addition to the light it scatters), known as both airglow and nightglow. Depending on where you are, that glow could be any combination of red, green, purple, and/or yellow. If you’d like to see a completely black sky, you’d have to go to the moon, which has no atmosphere and thus nothing to scatter or emit light.

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As human space exploration has evolved, trips offworld have grown longer and longer. In 1961, Yuri Gagarin spent less than two hours in orbit; today, it’s common for astronauts to stay in space for six months to a year. Because astronauts are spending larger portions of their lives hundreds of miles above us, the voting process has had to adapt. A pivotal moment occurred in September 1996, when NASA astronaut John Blaha went to the Russian space station Mir for a 118-day stay and completely missed voting in the 1996 presidential election. In response, Texas state Senator Mike Jackson proposed legislation to allow astronauts to vote in space. (Notably, many astronauts live in Texas because they train at the Johnson Space Center in Houston.) In 1997, NASA astronaut David Wolf, who was also aboard the Mir, became the first astronaut to successfully vote in space. Wolf told The Atlantic in 2016 that he was particularly moved by the experience, saying that voting “mak[es] a person feel like part of a civilization somewhere.”

World War II was the first time absentee voting occurred on a large scale.

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Historical evidence of absentee voting in the U.S. dates back to the 17th century, when some landowners could vote in absentia under certain circumstances. But the nation’s first large-scale absentee voting happened during the Civil War, for members of the military.

Although the idea of voting from a tin can some 254 miles above the planet may sound complex, the actual process is relatively straightforward. The county clerk from the astronaut’s home state (usually Texas) sends an electronic ballot to NASA; at the same time, an encrypted electronic ballot is sent to the orbiting astronaut via NASA’s Space Network, which manages all data and communication from the ISS to ground crews. The astronaut fills out the ballot (even putting “low-Earth orbit” on the address line) and sends it back using NASA’s Tracking and Data Relay Satellite to a ground antenna in New Mexico. NASA sends the ballot to Johnson Space Center, and then on to the appropriate county clerk. Throughout, only the clerk and the astronaut have access to the encrypted ballot to preserve its security. This entire process unfolded during the 2020 election, when NASA astronaut Kate Rubins submitted her ballot, calling it “an honor to be able to vote from space.”

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