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Science & Space?

The sky, the ocean, the moon, and why any of it happens. 47 questions and counting.

How do airplanes actually stay in the air?Wings deflect air downward, and the reaction pushes the plane up. The popular explanation about air traveling faster over…
How do vaccines work?They train your immune system on a harmless preview of a pathogen, so it recognizes the real thing and responds fast. The…
How does sunscreen actually work?Mineral filters like zinc oxide sit on the skin and scatter and absorb UV; chemical filters absorb UV and release it as…
How far away is the moon?About 238,900 miles on average, far enough to fit every other planet in the solar system in the gap. And it is drifting away…
How old is the Earth, and how do we know?4.54 billion years, give or take about 1 percent, measured by radiometric dating of meteorites and ancient minerals…
What causes lightning?Ice particles colliding inside storm clouds separate electric charge until the air itself breaks down and a giant spark…
What actually causes the seasons?Not distance from the sun; Earth is actually closest in January. Seasons come from the planet's 23.5-degree tilt, which…
What is a black hole?A black hole is matter crushed so dense that within a boundary called the event horizon, not even light moves fast enough to…
What is DNA?The molecule that carries the instructions for building and running a living thing, written in a four-letter chemical…
What is evolution, in plain terms?Populations change over generations because individuals with traits that help them survive and reproduce leave more…
How fast is the speed of light, and why does it matter?About 186,282 miles per second, or 299,792,458 meters per second, and it is the universe's speed limit for anything carrying…
What is the difference between a virus and bacteria?Bacteria are living single-celled organisms that reproduce on their own; viruses are not alive by most definitions and must…
Why do leaves change color in the fall?The yellows and oranges were in the leaf all summer, hidden under green chlorophyll. Shorter days shut down the chlorophyll…
Why is the ocean salty?Rain has spent billions of years dissolving minerals out of rock and rivers have delivered them to the sea, where water…
Why is the sky blue?Air molecules scatter short blue wavelengths of sunlight far more than red, so blue light bounces to your eyes from every…
Why do you get shocked by static electricity more in winter?Dry air. Humid air lets charge leak away from your body continuously, while winter air indoors can be drier than a desert…
What is a light year?A distance, not a time: how far light travels in one year, about 5.88 trillion miles. The nearest star beyond the sun is 4.2…
Why does the moon have phases?Because you see different fractions of its sunlit half as it orbits Earth. It is not Earth's shadow, which is a persistent…
What causes earthquakes?Rock along a fault sticks under strain until it suddenly slips, releasing stored energy as seismic waves. Most occur at…
What causes the tides?The moon's gravity pulls the ocean toward it, and there is a matching bulge on the opposite side because Earth itself is…
How does GPS actually work?Satellites broadcast the time continuously, and your device compares those timestamps to work out how far away each one is…
Why is blood red, and are veins really blue?Hemoglobin containing iron makes blood red, brighter when oxygenated and darker when not. Blood is never blue. Veins look…
Why are sunsets red and orange?Because low sun angles force light through far more atmosphere, scattering away the blue and leaving the reds and oranges to…
What is gravity, actually?Not a force pulling things together, on the best current description, but the curvature of spacetime caused by mass and…
Why is Pluto not a planet anymore?Because it has not cleared its orbital neighborhood, the third of three criteria the International Astronomical Union…
What is the difference between a comet, an asteroid, a meteor, and a meteorite?Asteroids are rocky, comets are icy and grow tails near the sun. A meteor is the streak of light when something enters the…
What causes a solar eclipse?The moon passing directly between Earth and the sun, casting a shadow. It works only because of a coincidence: the sun is…
How hot is the sun?About 10,000 degrees Fahrenheit at the visible surface and roughly 27 million at the core. Strangely, the outer atmosphere…
How does the water cycle work?Water evaporates, condenses into clouds, falls as precipitation, and returns to the ocean or soaks into the ground, driven…
How does photosynthesis work?Plants use light energy to combine carbon dioxide and water into sugar, releasing oxygen as a byproduct. Nearly all the…
What is the ozone layer, and did we fix the hole?A band of ozone in the stratosphere that absorbs most ultraviolet radiation. The hole over Antarctica is healing, and the…
How old is the universe, and how do we know?About 13.8 billion years, measured chiefly from the cosmic microwave background. Two independent methods now give slightly…
How do magnets work?Magnetism comes from the motion and alignment of electrons. In most materials the electron magnetic fields point randomly…
What is absolute zero, and can anything reach it?The temperature at which atomic motion reaches its minimum, minus 459.67 Fahrenheit. Nothing can reach it, because removing…
Why do humans have fingerprints?Not for grip, as long assumed. Testing found ridges may actually reduce friction on smooth surfaces. The better-supported…
Why does helium make your voice squeaky?It does not raise your pitch. Sound travels almost three times faster in helium, which shifts the resonant frequencies of…
Why does metal feel colder than wood at the same temperature?Because metal conducts heat away from your skin far faster. You are not sensing temperature, you are sensing heat loss…
Does time really move slower in space?Yes, and it is measured, not theoretical. Speed slows time and gravity slows time, so clocks on the space station and on GPS…
Why can you see the moon during the day?Because the moon is bright enough to compete with the daytime sky and it is above the horizon during daylight hours for much…
If there are billions of stars, why is the night sky dark?Because the universe has a finite age. Light from the most distant stars has not had time to reach us, and expansion…
How does carbon dating work?Living things absorb radioactive carbon-14 from the air, and when they die it decays at a known rate with a half-life of…
How do batteries actually work?A chemical reaction moves electrons from one electrode to another, and because the electrons cannot travel through the…
What causes volcanoes to erupt?Molten rock rises because it is less dense than the rock around it, and dissolved gases come out of solution as pressure…
What is the Milky Way?Our galaxy, a barred spiral containing a few hundred billion stars, about 100,000 light years across. The band of light…
How fast does sound travel?About 767 miles per hour in air at room temperature, which is roughly a mile every five seconds. It travels faster in water…
What causes ocean waves?Wind transferring energy to the water surface over distance and time. The water itself barely travels; the energy does…
How do plants know which way is up?Specialized cells contain dense starch grains that settle with gravity, telling the plant which way is down. Roots grow…