The behaviour of these functions is affected by settings in php.ini.
Here's a short explanation of the configuration directives.
The default latitude.
The default longitude.
The default sunrise zenith.
The default sunset zenith.
The default timezone used by all date/time functions if the TZ environment variable isn't set. The precedence order is described in the date_default_timezone_get() page. See List of Supported Timezones for a list of supported timezones.
Note: The first four configuration options are currently only used by date_sunrise() and date_sunset().