Planets · 1 of 6

Spotting the Planets

How can you tell a planet from a star?

Five wanderers, five tells, and the one line in the sky they never stray far from. Positions are computed for tonight.

You’ll be able to tell a planet from a star, and say which planet it is.

8 steps · about 6 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

JPL Horizons — the ephemeris convention this page's planetary positions follow
Meeus, Astronomical Algorithms, 2nd ed. (1998), ch. 32 and 41 — planetary positions and the magnitude phase terms
Mallama & Hilton, Astronomy and Computing 25, 10 (2018) — the modern planetary magnitude model
Kunitzsch & Smart, A Dictionary of Modern Star Names (2006) — Antares, "rival of Ares", the Greek Mars
HYG stellar database v4.2 — the background stars used for comparison

← 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

This line is the ecliptic, the Sun's yearly path, and every planet is on or near it. Five are bright enough for your eyes alone — the Greeks called them planētēs, wanderers. The next steps give five ways to tell one from a star.

Clue 1: it does not twinkle. Jupiter, at its next : outdoors the stars round it flicker and flash colour while it shines steady. A star is a point, which one pocket of air can shake. Jupiter is a tiny disc, its many light paths averaging out.

Clue 2: it is on the line. Planets orbit close to Earth's plane, so they stay within about 8°, a fist, of the ecliptic; Saturn sits beside it. Off the line, a bright stranger is a star. The Moon rides it too: a bright light beside the Moon is often a planet.

Clue 3: it is too bright for where it is. Venus reaches −4.9, twenty times the brightest star. If a constellation you know has a new brightest star, you have found a planet.

Clue 4: colour, the weak one. This orange-red light is not Mars but Antares, whose name means "rival of Mars". When Mars passes it, the two look like twins, and only the other clues tell them apart.

Clue 5: it moves. Run three weeks; the line is where Venus has been. Outdoors, check a suspect again in a week.

Your turn: which bright light is a planet? Nothing here is tagged. Look for a light too bright for its place, steady where the stars twinkle, on the Sun's line through the zodiac. Then press NEXT.

One is Jupiter. Hold it to all the clues: the more of them agree, the surer you can be.

Steady, and on the Sun's line
Too bright for its place
A week later, it has moved