Cosmira

Space · Cosmos

7 whys told, 3 on video

planets
stars
galaxies
black holes
exploration

Start with the most surprising

The whys of this universe

When the sun sinks, its light has to push through far more atmosphere to reach us. The blue scatters away on the way; the red survives. The sky doesn't change: the path lengthens.

Oddity
Video 27 s
4 min

Why are sunsets red?

Air scatters blue five to ten times more strongly than red, a law the future Lord Rayleigh described in 1871. At dusk, the light's grazing path leaves only the red.

Seen from the lunar surface: Earth as a perfectly black disc, ringed by a thin band of copper light, the only source lighting the ground in the foreground.

Oddity
4 min

Why does the Moon turn red during an eclipse?

Earth's atmosphere scatters blue light and bends red into the shadow. The eclipsed Moon glows with every sunset on the planet at once.

A very large cream Moon rises just behind a low silhouette of navy rooftops, in a deep violet sky flecked with a few cream dots; a thin paper halo rings the Moon, which looks enormous against the small rooftops.

Video 35 s
5 min

Why does the Moon look so big when it rises?

Locked by the same force that lifts our tides, the Moon turns once per orbit and keeps the same face forever toward Earth.

3 min

Why does the Moon always show the same face?

We often think the Moon doesn't spin. It's the opposite: if it didn't spin, that's precisely when we'd see all of its faces.

Past a certain size, gravity crushes every bump back toward the centre. A sphere is what a massive body always ends up becoming.

3 min

Why are planets round?

The asteroid Eros looks like a grey peanut, Itokawa like a battered potato. Below roughly 500 kilometres across, a body's gravity never gets the last word.

Their light crosses kilometres of restless air before reaching the eye. Planets, being closer, don't twinkle.

Video 47 s
3 min

Why do stars twinkle?

Olbers' paradox: the universe has an age, light from the most distant stars hasn't had time to reach us, and the light that does is stretched into the invisible.

Oddity
4 min

Why is the sky dark at night?

Night is not truly dark: radio telescopes pick up a glow in every direction, the light of the young universe stretched by expansion beyond what our eyes can see.

Newsletter

One why every Sunday, in your inbox.

Shh: Quaé is sleeping until the next why, Sunday morning.

Cosmira on video

All videos

Cosmira is the great dark pricked with ancient lights. Here you ask why stars twinkle, why the sky is dark at night, and why planets are round. The same light that travels all the way to us is the one that, lower down, paints the sky blue.

Birds · Sky

Plumaire

The universe next door

PlumaireBirds · Sky

Plumaire is the high plateau where migrations pass overhead, clouds take the shapes of animals, and birds ride the wind. Here, every why takes flight.

Explore Plumaire →All universes