mjaschen / astrotools
General Purpose Astronomy Library for PHP
Requires
- php: >=7.3
- ext-bcmath: *
Requires (Dev)
- ergebnis/composer-normalize: ^2.13
- friendsofphp/php-cs-fixer: ^2.18
- php-parallel-lint/php-parallel-lint: ^1.2
- phpunit/phpunit: ^9.5
- squizlabs/php_codesniffer: ^3.5
- vimeo/psalm: ^4.6
README
Astrotools is a general purpose PHP library for astronomy.
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:
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Please keep in mind, that the 0.1.x branch is no longer maintained and won't get any updates.
PHP 5
If you need to use Astrotools with PHP 5.4, 5.5, or 5.6, just require version 0.0.2:
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Please keep in mind, that the 0.0.x branch is no longer maintained and won't get any updates.
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.
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).
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:
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:
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:
6.2086583333
Local sidereal time
Local sidereal time for Berlin, Germany (longitude = 13.5 degrees east):
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:
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:
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:
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:
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:
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.
Astrotools currently provides the calculation of ΔT with polynomial expressions. Reasonably accurate values are provided for the timespan between the years -500 and 2150.
<?php use Astrotools\Time\DeltaT\PolynomialExpression; $deltaT = new PolynomialExpression(); echo $deltaT->getDeltaT(2016.125);
The code above produces the output shown below:
69.568218578125
Todo
- Support for microseconds in Julian day calculation
- Implement ΔT determination by table lookups
References
- Julian day formula - Astronomical Applications Department of the U.S. Naval Observatory
- Julian Date Converter - Astronomical Applications Department of the U.S. Naval Observatory
- Julian day - Wikipedia
- ΔT
- Astronomical Algorithms, Jean Meuss, 1998, ISBN 978-0943396613
- Polynomial Expressions For Delta T (ΔT)