Astrotools is a general purpose PHP library for astronomy., (*1)
Requirements
- PHP >= 7.3
-
bcmath extension
Older PHP versions
- 0.1.x branch supports PHP >= 7.0
- 0.0.x branch supports PHP 5.4 - 5.6. For details see the next section.
Installation
composer require mjaschen/astrotools
PHP 7.0, PHP 7.1, PHP 7.2
If you need to use Astrotools with PHP 7.0, 7.1 or 7.2 just require version 0.1:, (*2)
composer require mjaschen/astrotools:^0.1.0
Please keep in mind, that the 0.1.x branch is no longer maintained and won't get any updates., (*3)
PHP 5
If you need to use Astrotools with PHP 5.4, 5.5, or 5.6, just require version 0.0.2:, (*4)
composer require mjaschen/astrotools:0.0.2
Please keep in mind, that the 0.0.x branch is no longer maintained and won't get any updates., (*5)
Features
- Julian day calculation (forward/reverse)
- Sidereal time calculation (GMST, local sidereal time)
- Date of Easter calculation
- Time helper
Why not use PHP's calendar extension?
Some implemented features (e.g. calculation of Julian day or Date of Easter) are already provided by PHP's calendar extension., (*6)
These functions come with some problems, e.g. easter_date() can only calculate the Date of Easter for the timerange of unix timestamps (1970 January 1 to somewhere around 2037/2038)., (*7)
Usage Examples
Calculation of the Julian day from Date/Time
use Astrotools\Time\JulianDay;
$timestamp = new \DateTime('2015-02-25 12:01:36', new \DateTimeZone('Europe/Berlin'));
$jd = JulianDay::fromDateTime($timestamp);
echo $jd->getValue();
The code above produces the output shown below:, (*8)
2459283.3831366
Calculation of Date/Time from Julian day
use Astrotools\Time\JulianDay;
$jd = new JulianDay(2451545.0);
var_dump($jd->getDateTime());
The code above produces the output shown below:, (*9)
class DateTime#10 (3) {
public $date =>
string(26) "2000-01-01 12:00:00.000000"
public $timezone_type =>
int(3)
public $timezone =>
string(3) "UTC"
}
Calculation of sidereal time for a given Date/Time
Greenwich sidereal time
use Astrotools\Time\SiderealTime;
$dt = new \DateTime('2007-12-25 00:00:00', new \DateTimeZone('UTC'));
$st = new SiderealTime($dt);
echo $st->getSiderealTime();
The code above produces the output shown below:, (*10)
6.2086583333
Local sidereal time
Local sidereal time for Berlin, Germany (longitude = 13.5 degrees east):, (*11)
use Astrotools\Time\SiderealTime;
$dt = new \DateTime('2007-12-25 20:00:00', new \DateTimeZone('UTC'));
$st = new SiderealTime($dt);
echo $st->getLocalSiderealTime(13.5);
The code above produces the output shown below:, (*12)
3.1634161794
Time helper
Convert hours, minutes, and seconds to decimal time
use Astrotools\Helper\Time;
$time = Time::fromTime(6, 42, 23.1337);
echo $time->getValue();
The code above produces the output shown below:, (*13)
6.7064260278
Convert decimal time to hours, minutes, and seconds
use Astrotools\Helper\Time;
$time = new Time(6.7064260278);
printf('%02d:%02d:%02.4f', $time->getHour(), $time->getMinute(), $time->getSecond());
The code above produces the output shown below:, (*14)
06:42:23.1337
Convert between time and hour angle
use Astrotools\Helper\Time;
$time = Time::fromTime(6, 42, 23.1337);
echo $time->getHourAngle() . PHP_EOL;
echo Time::fromHourAngle(275)->getValue();
The code above produces the output shown below:, (*15)
100.596390417
18.333333333333
Date of Easter Calculation
use Astrotools\Time\DateOfEaster;
$doe = new DateOfEaster(2000);
echo $doe->getDate()->format('Y-m-d');
The code above produces the output shown below:, (*16)
2000-04-23
Calculation of ΔT
There exist multiple methods to get the value of ΔT for a given (decimal) year.
One can lookup the value in tables and interpolate
it for the wanted date or calculate it using
polynomial expressions., (*17)
Astrotools currently provides the calculation of ΔT with polynomial
expressions. Reasonably accurate values are provided for the timespan between
the years -500 and 2150., (*18)
<?php
use Astrotools\Time\DeltaT\PolynomialExpression;
$deltaT = new PolynomialExpression();
echo $deltaT->getDeltaT(2016.125);
The code above produces the output shown below:, (*19)
69.568218578125
Todo
- Support for microseconds in Julian day calculation
- Implement ΔT determination by table lookups
References
Wallogit.com
