Why does the date_sunset() function return false? What could be the possible causes?

In PHP, the date_sunset() function is used to calculate the sunset time for a specified time and location, returning either a timestamp or a formatted string. However, in some cases, the function may return false, typically indicating an error or calculation failure. This article will delve into several common causes that may lead to date_sunset() returning false, as well as how to avoid these issues.

1. Incorrect Parameter Passing

The standard usage of date_sunset() is as follows:

date_sunset(
    int $timestamp,
    int $returnFormat = SUNFUNCS_RET_STRING,
    float $latitude = ini_get("date.default_latitude"),
    float $longitude = ini_get("date.default_longitude"),
    float $zenith = ini_get("date.sunset_zenith"),
    float $gmtOffset = 0
): string|int|false

If certain parameters are not correctly passed, especially the latitude ($latitude) and longitude ($longitude), the function may return false.

Example:

// Incorrect example: missing latitude and longitude
$sunset = date_sunset(time());
if ($sunset === false) {
    echo "Unable to calculate sunset time";
}

Solution: Make sure to pass valid latitude and longitude values:

$sunset = date_sunset(time(), SUNFUNCS_RET_STRING, 31.7667, 35.2333, 90, 2);

2. Invalid Latitude or Longitude

If the latitude is outside the range of -90 to 90, or the longitude is outside the range of -180 to 180, the function will be unable to process correctly and will return false.

Example:

// Invalid latitude and longitude
$sunset = date_sunset(time(), SUNFUNCS_RET_STRING, 1234, 5678); // Invalid

Ensure the parameters fall within valid geographical coordinate ranges.

3. Timestamp Out of Supported Range

date_sunset() relies on timestamps for internal calculations. If the timestamp exceeds the integer range supported by PHP (especially on 32-bit systems), it may cause the function to return false.

Example:

// Timestamp exceeding 32-bit system range
$sunset = date_sunset(99999999999, SUNFUNCS_RET_STRING, 40.7128, -74.0060);

It is recommended to use time() or a reasonable strtotime() to generate a valid timestamp.

4. Incorrect Configuration Settings (php.ini)

PHP allows default latitude, longitude, and zenith values to be set through the php.ini file. If these values are not set or configured incorrectly, it may indirectly cause date_sunset() to malfunction.

How to Check:

echo ini_get('date.default_latitude');
echo ini_get('date.default_longitude');

If the output is empty or non-numeric, you should manually pass these parameters in your code.

5. Location Resulting in Inaccessible Sun Phenomena (Polar Nights)

In polar regions, during certain periods of the year, the sun never rises or sets (such as during the polar night or polar day). In such cases, date_sunset() may return false, as there is no "sunset" phenomenon on that day.

Example:

// Location in the North Pole, no sunset on a specific day
$sunset = date_sunset(strtotime("2025-01-01"), SUNFUNCS_RET_STRING, 89.9, 135.0);

6. Incorrect Time Zone or GMT Offset

The last parameter, $gmtOffset, controls the offset from GMT (UTC) in hours. If this value is set incorrectly, it may lead to unexpected results or return false.

For example, Beijing Time should be +8.0, but if set to -8.0, it may result in incorrect outcomes or false.

Conclusion

date_sunset() is a very useful time function, but it relies on several parameters, and any mistake in them can lead to false being returned. The correct usage should include:

• Clearly passing essential parameters like timestamp, latitude, and longitude

• Checking for issues in the php.ini configuration

• Avoiding calls in extreme geographical or time conditions