Comet Orbit and Tail Lab: Why the Tail Points Away
Use Kepler’s laws on a very stretched orbit: equal areas in equal times means racing past the Sun and crawling far away, and the solar wind pushes the tail straight away from the Sun.
Before you try
What if a comet’s tail really did trail behind it like smoke? Which way would it point after passing the Sun?
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What happened?
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A two-body orbit round a Sun-mass star; tail lengths are drawn to show the idea, not to scale.
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Try these ideas
- Pause the comet at perihelion and read its speed, then at aphelion. How many times faster is it?
- Set the eccentricity to 0 and see the tail behaviour on a circle.
- Build Halley’s orbit: perihelion 0.6 AU, period about 76 years.
Why it works
A comet is a lump of ice and dust a few kilometres across on a long, stretched orbit. Far from the Sun it is dark and slow. As it falls inward it speeds up, the ice turns to gas, and a glowing head (the coma) and a tail appear. Halley’s Comet comes within 0.6 AU of the Sun and swings out beyond Neptune, taking about 76 years per trip; it returns in 2061.
Kepler’s second law says a line from the Sun to the comet sweeps out equal areas in equal times, which is why it moves fastest at perihelion. The tail is not exhaust: sunlight and the stream of particles from the Sun (the solar wind) push gas and dust directly away from the Sun, so after perihelion the tail travels in front of the comet. In this lab you set the closest approach and the stretch of the orbit and watch all of this happen.
Check your understanding
Question 1 of 4
Where does a comet move fastest?
After a comet passes the Sun, its tail points
Halley’s Comet takes about 76 years per orbit. When it was last seen in 1986, when will it return?
Why does a comet have no tail when it is far from the Sun?
Explain it in your own words
What changed? Why did it happen? Where might you notice this in everyday life?
For parents & teachers
- Draw the orbit and mark where the tail points at four positions.
- Ask: why do we see “new” comets only once, while Halley’s keeps coming back?
- Relate the swept-area law to a swinging bucket on a rope.