Cosmos is an astronomy site for anyone who has looked up, seen a bright dot, and wanted a clear answer. It is not an encyclopedia of every object in the universe. It is a careful tour of the things you can actually learn, compare, and then go outside and find.
The name is the old Greek word for the universe as an ordered whole — not chaos, but a place with rules. That is the spirit of the site: real NASA numbers, real Moon-phase maths, real star patterns, and honest notes wherever a number is an approximation.
It was built by a class-8 student who likes space and got tired of astronomy pages that either read like a textbook or talked past beginners. Cosmos is for everyone, especially the person who just wants to know what they are looking at tonight.
Each page teaches one idea well. You can start anywhere and skip the rest.
All eight worlds with diameter, distance, orbit, day length, gravity, temperature and moons. A true-scale switch shows how small Earth is beside Jupiter. Every globe is drawn in CSS, not downloaded as a photo.
Sixteen patterns plotted from relative star positions and brightness. Each one has the myth behind the shape and a plain-language note on how to find it in a real sky.
A primer in eight chapters: light, gravity, stars, planets, galaxies, life, the beginning of the universe, and how to observe with your own eyes.
Tonight's phase is calculated from the synodic month — the 29.53-day cycle from one new Moon to the next. Pick any date and a month grid of tiny moons comes with it.
Fifty strange-and-true notes, grouped by solar system, stars, galaxies, travel, life and physics. Filter or search, then take what stuck into the quiz.
Four locked levels — Stargazer, Observer, Sky Navigator, Astronomer. Score 75% to unlock the next. Your rank stays in this browser and shows in the header. Every answer, right or wrong, gets an explanation.
A chat assistant that answers from the same planet, constellation, fact and Moon data the rest of the site uses. Ask “how big is Jupiter”, “Orion”, “moon”, “fact”, or “picture of the day” for NASA’s APOD.
You do not need a telescope to start. You need a few pictures in your head: where we live, what a star is, why the Moon changes shape, and how huge the distances really are.
Earth is a rocky planet orbiting an ordinary star we call the Sun. Together they belong to a flat, spinning disc of stars — the Milky Way. The pale band you see on a dark night is that disc viewed edge-on from the inside.
The Sun is not special. It is a main-sequence star, fusing hydrogen into helium in its core. That reaction has been running for about 4.6 billion years and has roughly as long again to go.
Close to the young Sun it was too hot for ice. Only rock and metal could stick together, so Mercury, Venus, Earth and Mars stayed small and solid. Past the frost line, ice survived, worlds grew fast, and Jupiter and Saturn became gas giants with no surface to stand on.
Uranus and Neptune, farther still, are ice giants: mostly water, ammonia and methane. Methane in their atmospheres is why they look blue. Pluto is a dwarf planet in the Kuiper Belt, not a ninth planet.
Light takes 8 minutes 20 seconds to travel from the Sun to Earth. You never see the Sun as it is — only as it was. A light-year is how far light travels in one year, about 9.46 trillion kilometres. It is a distance, not a length of time.
The nearest star after the Sun, Proxima Centauri, is 4.24 light-years away. Voyager 1, our farthest spacecraft, would need tens of thousands of years to get there. Space is mostly the gap between things.
Half the Moon is always lit by the Sun. Phases happen because the Moon orbits us, so we see different amounts of that lit half. A new Moon is the night side facing us; a full Moon is the day side. Earth’s shadow only matters during a lunar eclipse.
The Moon is tidally locked: it rotates once per orbit, so the same face stays pointed at Earth. The far side is not dark — it gets just as much sunlight. “Month” comes from “moon” for a reason.
A star is a ball of gas held up by fusion. When the fuel runs out, the ending depends on mass: a Sun-like star sheds its outer layers and leaves a white dwarf; a heavier star can explode as a supernova and leave a neutron star or a black hole.
Every atom of iron in your blood was forged in a star that died before the Sun was born. Constellations are not physical groups — the stars in a pattern are usually at wildly different distances, lined up only from our point of view.
The observable universe is about 13.8 billion years old and still expanding. Distant galaxies recede; their light stretches to redder wavelengths — redshift. Leftover glow from when atoms first formed, about 380,000 years after the Big Bang, still arrives as the cosmic microwave background.
Most of the cosmos is dark matter and dark energy: we measure their effects on galaxies and expansion, but we have not seen what they are made of. That is a real, open question — not a plot hole.
Astronomy is the art of not letting your brain round these down to “big”.
Earths would fit inside the Sun. The Sun itself is an average star.
For sunlight to reach Earth. Radio from Mars takes minutes; from Pluto, hours.
Stars in the Milky Way, give or take. Andromeda, our neighbour, holds more.
Across the observable universe — larger than its age in light-years, because space itself expanded.
A site that teaches space should be honest about space. Here is what is exact, what is rounded, and what will change next year.
Diameters, distances, gravity, temperatures and orbital periods follow NASA’s planetary fact sheet — the same tables textbooks use.
Confirmed moons are not a finished list. Saturn gained 128 in 2025 and overtook Jupiter. If you see a count here, it is right for that announcement, not for eternity.
The calculator assumes an even 29.530589-day cycle from a known new Moon in January 2000. The real orbit speeds up and slows down, so the result can be a few hours off. Fine for looking up. Not for launching anything.
Constellation drawings show the main stars and the shape people recognise. Real constellations contain many more stars. Positions are drawn to look right, not as a catalogue.
The true-scale toggle resizes every planet correctly. The gaps between them are still nothing like real. If distances were to scale, Neptune would be hundreds of screens away.
Planet, constellation, Moon and fact answers come from this site’s own data, so they match the pages. Open questions may use a local model when one is running; otherwise Beast says it does not know instead of inventing a number. NASA’s picture of the day needs a network connection.
You do not need an account to read the planets, watch the Moon, or
take the quiz. There is no advertising network and no third-party
analytics script. Quiz rank is stored only in this browser
(localStorage). An optional sign-in uses a session cookie
so Beast can greet you — it is not required, and it is not sold.
Links that leave Cosmos (NASA, and similar) are marked as ordinary
links you choose to click.
Skip this if you only came for the sky. The rest of the site does not depend on it.
Cosmos is plain HTML, CSS and JavaScript. Planets are CSS. The
starfield is a canvas. Constellations are SVG from coordinates. Moon
phase is arithmetic, not a lookup table. A small Node server handles
optional accounts; double-clicking index.html still
opens the guide without it.
Want a different accent colour? Open
css/style.css, change --teal near the top,
save, and refresh. The variable is shared across every page.