Johannesburg to London
The clock moves whether or not you are ready for it. This works out by how much, and what a bedtime walked an hour a night would look like on the way there or once you arrive.
London runs an hour behind Johannesburg. To arrive already keeping London hours, your bedtime has to move an hour later — from 10:00 pm to 11:00 pm, on your own clock at home. That is one night, so the table below starts one night before you fly.
| Night | Bed | Up | Moved | Sunset there on this clock | Sunrise there on this clock |
|---|---|---|---|---|---|
| Night 1 | 11:00 pm | 7:30 am | +1h | 7:50 pm | 7:55 am |
The gap, and why it is two numbers
In January, London runs 2 hours behind Johannesburg. In July it runs an hour behind. London puts its clocks forward for part of the year and Johannesburg does not, so a single figure would be wrong for months at a time. The planner above works from the difference on the date in its field.
What that asks of a bedtime
Taking the shorter way round the dial, the move is 2 hours later in January and an hour later in July. At the planner's usual step of an hour a night, that is 2 nights of shifting in January and 1 in July, either before you fly or after you land.
This is clock arithmetic and nothing else. It does not know how you sleep on aeroplanes, it makes no claim about how quickly anybody adjusts, and an hour a night is a step size rather than a finding. Shorten the step in the planner if a smaller one suits you.
Johannesburg to London through the year
This is a move of one or two hours, and which one depends only on London, because South Africa keeps the same clock all year. From the last Sunday of October to the last Sunday of March, London is on Greenwich Mean Time and two hours behind Johannesburg. For the rest of the year it keeps British Summer Time and is one hour behind. In the week the clocks change, the planner's figure changes with them, which is why it asks for the date you travel.
By the sun the gap is a little under two hours, since London sits 28 degrees of longitude west of Johannesburg, so the winter figure is the one that matches the daylight. The two cities are about 9,070 km apart on the great circle, most of it north rather than west, which is why the clocks move so little on a trip that long.
Going north-west, the move is later. A 10:00 pm bedtime in Johannesburg is 8:00 pm in London in January and 9:00 pm in July. At an hour a night, the planner spreads the move over two nights in the northern winter and one in the summer. Before you fly in January, that means staying up until 11:00 pm and then midnight on your own clock. After you land, it means going to bed at 9:00 pm London time the first night and 10:00 pm the second.
The seasons run the other way at the two ends. A July departure leaves the South African winter, when Johannesburg's sun sets at about 5:30 pm, for a London summer where it sets after 9:00 pm for much of the month. Cape Town keeps the same clock as Johannesburg, so Cape Town to London gives the same figures.
Going back
The return leg has its own page: London to Johannesburg.
Once you are there
With the clocks settled, the ordinary question comes back: what time to go to bed for the alarm you have set. That is the wake-time pages, which count in cycles rather than in zones.