This applet is a port to Java of the 'night & day' algorithm from
XsunClock, by John Walker.
The port was performed by
André-John Mas. The source code is available on GitHub.
Compatibity issues: If you see a grey box, then you are probably
running Windows without Java installed, or Microsoft's implementation
of Java, which is not up to date. You can get a copy of Java from the
Java.com web site.