;colony/science / Space & Astronomy
☾ Space & Astronomy
Space & Astronomy
The sky above the sky — seasons, phases, orbits, and the machinery of the solar system.
Read it your way
Every answer here is written twice. Flip the switch and the page rewrites itself.
Try it now · Plate 20
Why do we have seasons?
Slide Earth around its year and watch your daylight stretch and shrink.
PLATE 20 · TILT, NOT DISTANCE
Where in the orbit June · summer (north)
One full slide = one year. The axis never changes direction.
Your latitude 45°N
Daylight
15.4hours
Noon sun height
69°
Look at the bright part of your latitude line — that's your daytime. In June the north
leans toward the sun, so your line is mostly in the light: long days, high sun,
summer. Slide to December: same distance from the sun, but now you lean away —
short days, low sun, winter.
Every question
Space & Astronomy, answered twice.
Plate 20Open → Why do we have seasons? Earth is actually closest to the sun in January, mid winter up north. What makes the seasons is the lean of its axis. Plate 21Open → Why does the Moon change shape? The Moon never changes shape. What changes is where you are standing when you look at a half-lit ball. Plate 34Open → Why is the Moon out during the day? The number-one question kids ask their parents has a tidy answer: the Moon works day shifts too. Half of them, in fact. Plate 36Open → How does gravity actually work? The most famous force is also the weakest and the strangest: everything pulls on everything, including you on the Earth. Plate 41Open → What is a black hole, really? A black hole is a place where gravity gets so steep that the escape speed passes light itself. It pulls like any other mass, so miss it and you sail right past. Plate 61Open → Why does the Moon cause tides? The Moon pulls the oceans into a bulge — that part everyone knows. The puzzle is the second bulge, on the far side, which gives most coasts two high tides a day. Plate 69Open → Why do we have day and night? The sun does not rise or set. You do — carried around a spinning ball at over a thousand kilometres an hour. Plate 70Open → What causes a solar eclipse? Once in a while the Moon slides exactly in front of the Sun and drops a shadow on Earth. Stand in the dark heart of it and the Sun vanishes in daytime. Plate 71Open → Why do planets orbit the Sun? A planet in orbit is in permanent free fall: forever dropping toward the Sun, forever moving sideways fast enough to miss it. Plate 104Open → Why do comet tails point away from the Sun? The Sun blows a comet's tail straight outward, so it always points away from the Sun, even running ahead of the comet on its journey back home. Plate 105Open → Why don't satellites fall down? A satellite is falling toward Earth every second of every day. It never lands because it's moving sideways so fast — about 7.8 km/s — that the ground curves away beneath it as fast as it drops. Plate 106Open → What is a light-year? Light is the fastest thing in the universe, yet space is so vast that sunlight takes 8 minutes to reach us and the next star's light takes over 4 years. Look up, and you're always seeing the past. Plate 107Open → Why do stars twinkle but planets don't? A star is so far away it's a single point of light, and one thin beam gets jostled by turbulent air, so it shivers. A planet is a tiny disc, many beams at once, and their flickers cancel out into a steady glow. Plate 108Open → How do we weigh a planet? You can weigh a planet you'll never touch just by watching its moon. A heavy planet pulls hard, so its moon must race round fast — the moon's speed and distance hand you the planet's mass. Plate 154Open → Why is space black if there are so many stars? If the universe were infinite and unchanging, every line you looked along would end on a star, and the whole night sky would blaze like the Sun. It doesn't — and the reason rewrote our picture of the cosmos. Plate 158Open → Why do astronauts float if gravity is still strong up there? Astronauts don't float because gravity is missing. At the Space Station gravity is still about 90% as strong as on the ground. They float because they and the station are falling around the Earth together, and never landing.
— ;colony