marando / php-iers
A PHP package that simplifies obtaining Earth rotation values from IERS bulletins.
Requires
- php: >=5.6
Requires (Dev)
- phpunit/phpunit: ^5.0
README
phpIERS is a PHP package that simplifies obtaining Earth rotation values published by the International Earth Rotation and Reference Systems Service.
Installation
With Composer
$ composer require marando/php-iers
Usage
Creating an Instance
You can create an instance from a standard of modified Julian day, as well as the current time:
IERS::jd(2451545.5); // Julian Day IERS::mjd(51545.5); // Modified Julian Day IERS::now(); // Current time
Delta T (ΔT)
Delta T can be interpolated for any date from the year 1657 to present, and future dates can be predicted up to ten years into the future. All values returned represent seconds of time
IERS::jd(2451545.5)->deltaT(); // Result: 63.829474585665 IERS::jd(2351545.5)->deltaT(); // Result: 19.251735262674
UT1-UTC (dut1)
The value of UT1-UTC (dut1) is returned in seconds of time:
IERS::jd(2451545.5)->dut1(); // Result: 0.354633 IERS::jd(2457545.5)->dut1(); // Result: 0.1725287
TAI-UTC (Leap Seconds)
The total number of leap seconds accrued as of the specified date can be obtained as shown:
IERS::jd(2451545.5)->leapSec(); // Result: 33 IERS::jd(2457545.5)->leapSec(); // Result: 36
Celestial Pole Offset (X and Y)
The celestial pole offsets X and Y are returned as seconds of arc:
IERS::jd(2457545.5)->x(); // Result: 0.086606 IERS::jd(2457545.5)->y(); // Result: 0.012592
Updating Local IERS Data
The package comes with a cached set of IERS data that will only be updated when you manually call the following update function:
IERS::update()
This allows you to control when the data update occurs to avoid lengthy delays in your code when updates are being downloaded. It's up to you when and how you want to handle updating, but a good idea is to set up a late night cron job to perform the update process.