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When programming in PHP, the date_sunset() function is a common tool that calculates sunset time based on specified dates and geographic locations. Is the calculation of this function accurate? In order to verify its accuracy, we can compare the calculation results of the date_sunset() function with the sunset time provided by NASA. This article will show how to write code in PHP, get sunset times and compare them with NASA official data.
The date_sunset() function is a date-time function built in PHP, which is used to calculate the sunset time at a specific location. Its basic syntax is as follows:
date_sunset(time, format, latitude, longitude, zenith, gmt_offset);
time : timestamp, used to calculate the sunset time of the corresponding time, and the current time is used by default.
format : The format of the return value can be 0 (returns Unix timestamp) or 1 (returns the specified date format).
latitude and longitude : the latitude and longitude of the geographical location.
zenith : The astronomical height of sunset, usually 90.83 degrees.
gmt_offset : The time difference with the GMT time zone, usually 0.
Here is a simple example, using date_sunset() to calculate the sunset time of a city and output the result:
<?php
// Set the city's latitude and longitude and time zone
$latitude = 40.7128; // The Latitude of New York City
$longitude = -74.0060; // Longitude of New York City
$timezone_offset = -5; // Eastern Time
// Get the current timestamp
$time = time();
// Calculate the sunset time，The format is Unix Timestamp
$sunset_timestamp = date_sunset($time, SUNFUNCS_RET_TIMESTAMP, $latitude, $longitude, 90.83, $timezone_offset);
// Output sunset time
echo "The local sunset time is: " . date('Y-m-d H:i:s', $sunset_timestamp);
?>
NASA provides accurate data on sunset and sunrise times, derived from precise astronomical calculations and models. In order to verify the accuracy of the date_sunset() function, we can compare the sunset time calculated by PHP with the time provided by NASA.
Here is an implementation idea:
Get the date_sunset() calculation result of your location.
Get the sunset time at the same moment from the official NASA website.
Compare the differences between the two.
NASA provides APIs that allow us to obtain precise data on sunset times. You can access the NASA API to get the latest data. For a simple demonstration, let's say we've got the sunset time in New York City.
Here is a PHP example that calls the NASA API to get sunset time:
<?php
// set up API URL，Assumptions API Address is NASA Sunset Time Interface
$url = "https://api.m66.net/sun_data?lat=40.7128&lon=-74.0060"; // Replace with actual NASA API address
// use cURL Get data
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($ch);
curl_close($ch);
// Resolved returned JSON data
$sunset_data = json_decode($response, true);
$official_sunset_time = $sunset_data['sunset_time']; // Assumptions返回的是一个 'sunset_time' Fields
echo "NASA The official sunset time is: " . $official_sunset_time;
?>
A slight difference may occur when comparing the date_sunset() function with the official sunset time provided by NASA. date_sunset() uses an astronomical algorithm to estimate sunset time, while NASA's data is calculated based on more accurate observations and models.
Generally speaking, the time calculated by date_sunset() will be very close to the official time, but there may be a little deviation due to the simplification of the algorithm or time zone differences. If you need higher precision sunset times, it is recommended to use APIs like NASA provided or other astronomical observation data sources.
