Why auroras glow green, red and purple
Energetic particles make oxygen and nitrogen in the upper atmosphere emit light. The gas, its energy state and altitude help determine the...
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Space Facts
Extraordinary worlds, surprising connections, and the science behind them.
Why looking across space means looking into the past
Moonlight reaches us about 1.3 seconds after leaving the Moon; Andromeda’s light takes roughly 2.5 million years. The same finite speed connects...
Why Earth’s rotation takes less than 24 hours
Earth turns once relative to distant stars in about 23 hours 56 minutes. Its journey around the Sun explains why the familiar...
Why the Sun’s light is white, even when it looks yellow
The Sun emits a broad mixture of visible wavelengths that our eyes perceive as white. Air, camera settings and scientific image processing...
Why Saturn’s rings sometimes seem to disappear
Saturn keeps its rings when they turn edge-on to Earth. Their changing appearance follows the geometry of a tilted planet, a thin...
How a star’s tiny apparent shift reveals its distance
Earth’s orbit gives astronomers changing viewpoints on the stars. Measuring the resulting apparent shift turns a small angle into a distance, provided...
Why stars twinkle while planets often look steady
Moving air distorts arriving starlight. A planet’s larger apparent disk helps average out brightness changes, while stars near the horizon face a...
Why seasons on Uranus last about 21 Earth years
An 84-year orbit sets the pace of Uranus’s seasons. Its nearly sideways spin axis makes the poles alternate between prolonged daylight and...
Why astronauts float while Earth’s gravity stays strong
Earth’s gravity remains strong at space-station height. Shared free fall, sideways motion and the absence of a supporting floor explain why astronauts...
The Moon’s far side gets sunlight, too
The Moon keeps roughly the same face toward Earth, but its daylight follows the Sun. Rotation and changing illumination explain the difference.
Why comets can have two different tails
A broad dust tail and a straighter ion tail respond differently to the Sun, so they can spread across the sky in...
Why black holes don’t swallow everything around them
Mass, distance and an object’s motion matter. A black hole’s event horizon marks the boundary from which even light cannot escape.