Space
Blue stars are hotter than red stars
A star's colour reveals its surface temperature: blue stars are hottest, while red stars are cooler.
More in Space
A day on Venus is longer than its year
Venus takes 243 Earth days to spin once, but only 225 to orbit the Sun — so a single Venusian day outlasts its year.
Saturn would float in water
Saturn is mostly hydrogen and helium, giving it a density lower than water. Find a bathtub big enough and the ringed planet would bob on the surface.
The Moon drifts 3.8 cm away every year
Tidal friction slowly pushes the Moon outward and lengthens our days. In the age of dinosaurs a day lasted about 23 hours.
The first photo of a black hole used an Earth-sized telescope
In 2019 eight radio observatories across the planet were linked into one virtual dish the width of Earth. It imaged M87*, a black hole 55 million light years away.
Time itself slows down near a black hole
Gravity stretches time. Watch someone fall toward the event horizon and they appear to slow, redden and freeze forever — while for them, the fall takes only moments.
Black holes slowly evaporate
Stephen Hawking showed black holes leak faint radiation and shrink. A stellar-mass one would take about 10^67 years to vanish — far longer than the universe has existed.