Earth & Space

7 breaks

Planets, weather, oceans and the sky above them.

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Why the night sky is dark: Olbers' paradox and the light that hasn't arrived yet Go outside and look between the stars: it's dark. That's strange. In an endless, unchanging universe, every line of sight would end on a star, and the whole… Earth & Space4 min read Why there are two high tides a day: the Moon pulls the near sea harder and the far sea softer The sea rises twice a day, not once, and the second high tide happens on the side of the Earth facing away from the Moon. Why? The Moon pulls the near ocean a… Earth & Space4 min read Why the Moon changes shape: always half lit, and only part of it faces you Ask why the Moon changes shape and most people blame the Earth's shadow. It is a natural guess, and it is wrong: the Moon is half lit by the Sun all the time… Earth & Space4 min read Why planets speed up near the Sun: Kepler's equal-areas law Earth moves at 30.29 km/s near 3 January and 29.29 km/s near 4 July, with nothing pushing it along. The rule behind the change is Kepler's equal-areas law: a… Earth & Space3 min read Why one day on Mercury lasts two Mercury years Mercury circles the Sun in 88 Earth days and spins once every 58.6 days. That odd pairing, three spins for every two orbits, means one sunrise to the next… Earth & Space3 min read Earth is closest to the Sun in January. So why is that winter? Summer can't be caused by being closer to the Sun: Earth makes its closest pass around 3 January and is farthest around 4 July. The distance changes by only… Earth & Space4 min read Why Mars sometimes walks backwards across the sky Every 26 months or so, Mars slows down, stops, and drifts backwards against the stars for a couple of months before carrying on. Ancient astronomers built… Earth & Space4 min read