front page



Daylight moves across the face of the globe East to West, and we don't want to change that. But the clocks can be displayed with cities running East to West or West to East, while you read Left to Right. By default the display runs East to West (as it is read Left to Right), to tie the progression of the Sun to the reading direction.

We are, however, used to looking at the globe from the outside and from that vantage point daylight progresses East to West alright, but Right to Left, so this direction may seem more natural.

No problem, you can choose a West to East display and in this case daylight will progress Right to Left, like on a globe. The choice will be remembered between visits if you allow cookies.



Sources for Time Zone and Daylight Saving Time Data.
The clocks page uses the public-domain time zone database tz/zoneinfo to drive a php clock with the calculated local time. Day, night and twilight hours are calculated from a modification of Paul Schlyter's sunrise program. The twilight is civil twilight and begins when the center of the Sun reaches 6 degrees below the horizon. Sunrise and sunset occur when the Sun's upper limb reaches 35 arc minutes below the horizon, to account for atmospheric refraction.

A clock face is normally white during the day, gray during twilight and dark at night. Special clocks can appear on special occasions. The clocks page is refreshed automatically every 10 seconds, if javascript is enabled.


Q: The 10 second update is sometimes smooth, sometimes jerky. Why is that?

A: It's an interesting problem to try to minimize, I don't know if it can be got rid of completely!

Every 10 seconds all the clocks have to be updated. (Your PC cannot do that -- using java or javascript -- because it doesn't know how local time is defined around the globe or when the sun rises or sets there.) The server has code for that, so *it* has to make the new images.

To avoid a flicker *every* 10 seconds the browser prefetches the next pictures while the current ones are displayed -- javascript can do that. 10 seconds later when the browser needs the new pictures, it finds them already in its cache so the update is fast and smooth.

But it is not exactly 10 seconds. Some time is taken by the browser to render the page and fetch the next images and that time will vary from PC to PC. So every so often the pictures in the cache are not the required ones (they are off by more than 10 seconds) and the browser has to fetch the pictures in real time. That's when you notice a flicker.