How the Sky Turns · 3 of 8

The Southern Cross

How do you find south from the stars, with no pole star to point the way?

There is no south pole star. Crux and the two bright Centaurs are how you find the pole anyway.

You’ll be able to find the south celestial pole from Crux and the Pointers.

8 steps · about 6 min

Before this: Measure the Sky with Your Hand (5 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

HYG stellar database v4.2 — star positions, magnitudes and every separation quoted here
Kervella et al., A&A 598, L7 (2017) — masses and orbit of the Alpha Centauri system
Anglada-Escudé et al., Nature 536, 437 (2016) — Proxima b, and Proxima at 4.24 ly
Meeus, Astronomical Algorithms, 2nd ed. (1998), ch. 17 — great-circle geometry of the pole hop

← 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

Crux is the smallest constellation, yet two of its stars are first-. Its long axis runs from Gacrux, a cool red giant at the top, to Acrux, a hot blue-white pair at the foot. That line is the instrument.

↺ Colour is a thermometer, from Orion: The Hunter

A degree from Mimosa sits the Jewel Box, NGC 4755: in binoculars, blue-white stars round one red supergiant. The dark patch beside the Cross is the Coalsack, a dust cloud 600 light-years off, and the head of the Emu in the Sky.

No bright star marks the south pole: Polaris Australis, a degree off, is too faint for most skies. So build one: run the Cross's axis past Acrux 4.5 times its length to the south celestial pole. Straight below is south.

The two brilliant stars east of the Cross are the pointers; their tags say they are no pair. From their ringed midpoint drop a line at right angles: where it meets the Cross's axis is the pole. Two lines agreeing beat one remembered.

The trap: the False Cross, three fists west — bigger, dimmer, more even, with no pointers. Use it and your south is out by 15°.

Nine hours: it wheels round the pole.

↺ Circumpolar, from Why the Sky Moves

Walk south and the pole climbs: its altitude is your latitude, 10° a fist.

Drop to the horizon for south. Five flags fly the Cross: Australia, New Zealand, Brazil, Papua New Guinea and Samoa.

4.5 Cross-lengths on, checked by pointers
Not the False Cross, which has no pointers