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The universe from its beginning to the planets next door, and how people have gone out to look. Each note explains one thing in plain words and links to the questions it raises.
14 notes from Graphite. Free to read, with no account. Nothing here is for sale.
Start here
The note that answers the topic’s biggest question, then the two it leads to most directly.
Start here
The universe is all of space and time and everything in them. The part we can see is about 93 billion light-years across and 13.8 billion years old, and most of it is dark.
Graphite6 min read
Then
The Sun is made mostly of hydrogen and helium, as hot electrically charged gas. Fusion in its core turns hydrogen into helium and some mass into the energy that lights the solar system.
Graphite6 min read
And then
A black hole is a region of space where matter is packed so tightly that nothing, not even light, can escape its gravity. How they form, how big they are, and how we know they're real.
Graphite6 min read
Every note
The three above, then the rest. Each answers one question and links to the notes it leads to.
The Moon is made of rock much like Earth's mantle, rich in oxygen, silicon, magnesium, iron, calcium and aluminum, around a small iron core. It most likely formed from debris of a giant impact.
Graphite6 min read
Yes. Twelve astronauts walked on the Moon between 1969 and 1972, and the evidence is still there to check, from 382 kg of lunar rock to mirrors that observatories hit with lasers today.
Graphite6 min read
The solar system is the Sun and everything its gravity holds: eight planets, five official dwarf planets, hundreds of moons, and countless asteroids and comets out to the distant Oort cloud.
Graphite6 min read
The International Space Station is a laboratory orbiting about 400 km above Earth, run by five space agencies and lived in without a break since November 2000. How it works and when it retires.
Graphite6 min read
The Milky Way is the galaxy we live in: a flat, barred spiral of 100 to 400 billion stars about 100,000 light-years across, with a black hole of 4 million Suns at its center.
Graphite6 min read
Mars is a cold desert world with air about 1% as thick as Earth's, giant volcanoes and planet-wide dust storms. What it is like, where its water went, and what stops people living there.
Graphite6 min read
Venus is about 465°C at the surface, hotter than Mercury, because its thick carbon-dioxide air traps heat in a runaway greenhouse effect. How it got that way, with the numbers.
Graphite6 min read
Pluto is not a planet because in 2006 astronomers decided a planet must clear its orbit, and Pluto shares its path with countless icy bodies. The rule, why it came, and the case against it.
Graphite6 min read
The Big Bang theory says the universe expanded from an extremely hot, dense state about 13.8 billion years ago. It was not an explosion in space, and three lines of evidence back it.
Graphite6 min read
The northern lights are caused by charged particles from the Sun, guided by Earth's magnetic field, striking oxygen and nitrogen high in the air and making them glow green, red and blue.
Graphite6 min read
The Fermi paradox is the gap between how likely alien civilizations seem, in a huge and ancient galaxy, and the total lack of evidence for them. Where it came from, and the main answers.
Graphite6 min read
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