Phase Of The Moon
Please be patient while the applet loads
The user interface in the applet works as follows:
Time Display Box
Shows the date and time at which the phase will be
This can be edited directly, or adjusted using the buttons.
When the desired value is shown, press the OK button.
<< and >> Buttons
Set the time at which the phase will be calculated,
respectively back or forward a day from that currently
Set the time at which the phase will be calculated to be
the current clock time.
Do the calculation for the time displayed.
A Note On GMT Times
This applet uses the standard Java facilities to convert
time to GMT.
Most current browsers implement this correctly; however a bug
has been introduced in the JDK1.1 and HotJava 1.0
implementations such that in fact BST is displayed in the
summer, not GMT. If you are running under one of these
implementations, please read "GMT" as "UK local time".
I hope this problem will be corrected before it becomes too
Accuracy of calculation
The applet calculates the phase of the Moon, using
methods taken from the book "Practical Astronomy with your
Calculator" by Peter Duffett-Smith (ISBN 0-521-35699-7).
These methods typically give timing accurate to around 10 or
20 minutes, For comparison, accurate times for the present
decade are available at the US Naval Observatory.
The phase is that seen at the centre of the Earth. For any
other location there would be a correction for parallax which
would be of similar magnitude to the error inherent in the
calculation. If you're interested, the source code for this
applet is available here (under the GNU GPL).