Planets · 5 of 6

Racing and Crawling

Why does Halley’s Comet race past the Sun and crawl far from it?

Why Halley's Comet rounds the Sun at 55 km/s and crawls past Neptune's distance at under 1: the line from the Sun sweeps equal areas in equal times.

You’ll be able to explain why a comet races past the Sun and crawls at the far end of its orbit.

5 steps · about 4 min

Where and which night

Working out when this is best placed from where you are…

Where

Which night

Date

Time

Kept for this guide only, until you change it here — your map settings, and every other guide, stay as they are.

Print, play outside or present

Present on a big screen

Scan with a phone's camera, or open

Sources

Minor Planet Center orbit of 1P/Halley (1986), as carried in Stellarium's ssystem_minor.ini
Wikipedia, "Halley's Comet" — its orbit, and its speed, 54.55 km/s at perihelion and 0.91 km/s at aphelion, and its last aphelion, in December 2023
NASA Science: Orbits and Kepler's Laws — the second law, equal areas in equal times
NASA Science: 1P/Halley — its 76-year period and the 2061 return
Meeus, Astronomical Algorithms (2nd ed.), ch. 33–34 — positions from orbital elements

← GUIDES

More below ↓

With a keyboard, focus the sky, aim it with the up and down arrow keys, and press Enter to drop the pin at the centre of the view; or press Show me.

You are here

Settings

Screen

Night mode Turns every page red, to keep your eyes adjusted to the dark.

High contrast Bolder constellation lines, larger and brighter names on the sky, and stronger text and edges everywhere. Starts on if your device asks for more contrast.

Reduce motion The camera cuts to where it is going instead of flying there, and panels and sheets appear without sliding. Starts on if your device asks for less motion.

Battery saver Draws the sky thirty times a second at most: smoothness traded for battery.

Night brightness Dims the screen below your phone’s lowest setting, down to a fifth, while night mode is on.

Clock and voice

Clock How every time is written. Until you choose, your language’s own clock decides.

D describes What D says about the view on the sky: one sentence, or in full with the field, the constellation and five names.

Sounds Quiet tones as you use the map: a tick as you drag the clock past a mark or dusk, a chime for the star you pick — higher for hotter stars — and a low swell while a figure is out of the dome. Made in your browser, and off until you turn them on.

All settings and your progress

Halley's Comet on its best night of 1986, from where you are. It rounded the Sun at 55 km/s — the Atlantic in two minutes; past Neptune it creeps at 0.9 km/s. It turned round out there in December 2023 and is falling back, to round the Sun in 2061.

↺ Halley's Comet, from Comets

Its orbit from above, the rings the planets' distances. Drag and watch the tag: falling toward the Sun it speeds up like a dropped ball, whips round, then slows climbing away, like a ball thrown upward.

Each wedge is 4 years of the dashed line's sweep: fat by the Sun, thin far out.

The Earth keeps the same law. It is nearest the Sun, and quickest, in early January, so the northern winter half of its orbit, September equinox to March, takes 179 days, and the summer half 186.

One orbit, one law. The Earth keeps it too: fastest each January, nearest the Sun.

Faster falling in, slower climbing out
Kepler's law, equal areas in equal times
Back to round the Sun in 2061