Science labs › Earth and space › Comet Orbits
Why does a comet grow a tail near the Sun, and why does it rush past so fast?
Comet Orbits lab · Last updated: 16 October 2026
You follow an icy comet on its long, stretched orbit round the Sun. They see it grow a glowing tail as it gets close, and watch it whip past the Sun before slowing down on its way back out. It shows how gravity shapes orbits across the whole solar system.
What you'll discover
- A comet is a lump of ice and dust that heats up near the Sun, giving off gas and dust that form its tail.
- The tail always points away from the Sun, pushed by sunlight and the solar wind.
- A comet moves fastest when closest to the Sun and slowest when furthest away.
The science in plain words
A comet is a small body of frozen water, frozen gases, rock and dust, often only a few kilometres across. Most comets spend their time far beyond the planets, where they are frozen solid and dark. Their orbits are long, stretched ellipses, so some swing in close to the Sun before heading back out to the cold outer solar system.
As a comet approaches the Sun, sunlight warms its surface. The ice turns straight into gas without melting, a change called sublimation, and the gas carries dust with it. This forms a glowing cloud round the core, called the coma, and long tails. Comets usually have two: a curved dust tail and a straight, bluish ion tail of charged gas. Both point away from the Sun, because sunlight and the solar wind push them outwards, so when the comet heads back out its tail goes in front.
A comet speeds up near the Sun because gravity pulls it inwards and it gains speed as it falls, just as a ball speeds up rolling downhill. Further out it climbs away against gravity and slows down. Johannes Kepler described this pattern: a line from the Sun to an orbiting body sweeps out equal areas in equal times. Halley's Comet follows such an orbit and returns roughly every 76 years.
Where it fits
- India, NCERT: Goes beyond the NCERT syllabus for classes 6 to 10; it builds on Class 6 Beyond Earth and Class 9 Gravitation.
- United States: Grades 6 to 8
- Next Generation Science Standards: MS-ESS1-2
Common questions
Why does a comet have a tail?
Near the Sun, sunlight heats the comet's ice so it turns into gas, releasing dust too. Sunlight and the stream of charged particles from the Sun, called the solar wind, push this gas and dust away, stretching it into tails that can be millions of kilometres long.
Which way does a comet's tail point?
A comet's tail always points away from the Sun, not behind the comet. Sunlight and the solar wind push the gas and dust outwards. When the comet travels back out towards the edge of the solar system, its tail actually leads the way.
When will Halley's Comet come back?
Halley's Comet returns about every 76 years. It was last seen from Earth in 1986 and is expected to be visible again in 2061. It is the best known periodic comet, and records of its appearances go back more than two thousand years.
Related labs
- Orbital Mechanics: Newton's cannonball: how fast must you fire it sideways so it never lands?
- Solar System: A desk orrery run by real gravity: why does Mars take longer than Earth to go round?
- Black Holes: Shine light past a black hole: does it bend, or fall in for ever?
See all earth and space labs or every Taz science lab.
Try it yourself
The Comet Orbits lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.