Finding south without Polaris

Explainer · 0:40 · silent, with on-screen words

Why Polaris barely clears the horizon from Guyana, and how the Southern Cross finds south instead: rising, upright and setting over Georgetown on 15 April 2027.

The video file (MP4, 1983 kB)

Shows the northern and southern skies over Georgetown (6.80° N, 58.16° W) on the night of Thu 15 Apr 2027, Guyana time.

Chapters

  1. 0:00 Polaris from Guyana
  2. 0:10 The Southern Cross
  3. 0:21 Upright: south
  4. 0:30 Any time it is up

From the lesson Finding Objects in the Night Sky Without Polaris.

What the video shows, in words

A silent 40-second explainer drawn with the site’s own horizon charts, over Georgetown, Guyana, on the night of Thursday 15 April 2027.

Facing north at 21:22 GYT, when the Big Dipper’s pointer stars Dubhe and Merak stand highest (Dubhe 35° up), they point down to Polaris, which is only 6.6° above the horizon; through the day it swings between 6.3° and 7.5°, because from 6.8° N the north celestial pole is 6.8° up.

Facing south, the Southern Cross rises at 17:35 GYT (Acrux, in the SSE) and climbs on its side. At 22:45 GYT Acrux crosses the meridian 20° up and the Cross stands upright. Its long axis, Gacrux to Acrux, is 6.0° long; 4.5 of those lengths on from Acrux is the south celestial pole, 6.8° below the horizon, so the point on the horizon straight under it is due south. Alpha and Beta Centauri, the Pointers, follow the Cross. Acrux sets at 03:54 GYT in the SSW.

Star places from SIMBAD; times, heights and bearings computed with astronomy-engine for Georgetown (6.80° N, 58.16° W) in Guyana time (UTC-4).

  1. 0:00 From Guyana the North Star is no help: it sits just above the northern horizon. The Southern Cross finds south instead.
  2. 0:04 Facing north at 21:22 GYT: the Big Dipper’s pointers lead down to Polaris, only 6.6° up. Trees, hills or haze on that horizon hide it.
  3. 0:10 Face south instead. From 19:45 GYT the Southern Cross climbs in the south-south-east, leaning 53° to the left (east) at first and slowly straightening, with the two Pointers following it up.
  4. 0:21 At 22:45 it stands upright, Acrux 20° up. Carry the long axis on about 4.5 times past Acrux: that is the south celestial pole, 6.8° below the horizon. Straight under it is due south.
  5. 0:30 Afterwards it leans over to the south-west, but its long axis still points at the pole, so it finds south whatever its tilt.
  6. 0:36 Upright about two hours earlier each month: 22:45 in mid-April, 20:47 in mid-May, 18:45 in mid-June (GYT).

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