libthesky

Fortran library to compute positions of celestial bodies

https://github.com/marcvdsluys/libthesky

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Fortran library to compute positions of celestial bodies

readme.org

#+title: libTheSky: Readme

* Summary
+ Package:      libTheSky
+ Description:  Fortran library to compute properties of objects in The Sky
+ Homepage:     https://libthesky.sourceforge.net
+ Copyright:    Copyright (c) 2002-2025  Marc van der Sluys - Nikhef/Utrecht University - marc.vandersluys.nl


The package libTheSky provides a Fortran library to compute the positions and other properties of celestial
bodies (Moon, planets, comets, asteroids, stars), events (e.g.  lunar phases) and coordinate
transformations. It forms the core of the software that is used to create the Dutch popular-astronomy website
https://hemel.waarnemen.com.  To download the libTheSky package, read the code documentation, or to contact
the developer, see: https://libthesky.sourceforge.net/



* Installation

** Dependencies

libTheSky is written in Fortran, hence you will need a Fortran compiler.  Gfortran, part of gcc, is a free,
open-source Fortran compiler included in many GNU/Linux distributions and available from
https://gcc.gnu.org/fortran/.

The default installer uses CMake to configure and compile the code.  CMake is also open-source software, also
included in most GNU/Linux distributions, and can be downloaded from https://www.cmake.org/.  Alternatively,
you can create your own Makefile or compile and link the code manually.

libTheSky needs the Fortran library libSUFR in order to compile and run.  libSUFR is free and open software,
and available under the EUPL v1.2 from https://libsufr.sf.net/.


** Unpacking

After downloading from libthesky.sf.net, you can unpack the tarball and cd into its directory by doing e.g.:
  #+begin_src bash
    tar xfz libthesky-0.0.1.tar.gz
    cd libthesky-0.0.1/
  #+end_src
(replace "0.0.1" with the correct version number).


** Configuring, compiling and installing

To configure, compile and install the code and data files (in the CMake (not Linux! - see below) default
system directories ~/usr/local/...~), from the main package directory (the one that contains the file
CMakeLists.txt), do:
 #+begin_src bash
   mkdir build && cd build/
   cmake ..
   make
   sudo make install
 #+end_src
The second step above configures the code and should find your Fortran compiler and libSUFR.  The third step
compiles and links the code, and the last step installs it on your system - for which you need root
priveliges, hence the 'sudo' command.

To install the package in a specific system directory, e.g. the Linux default ~/usr/...~ (RECOMMENDED), do:
 #+begin_src bash
   mkdir build && cd build/
   cmake -DCMAKE_INSTALL_PREFIX:PATH=/usr ..
   make
   sudo make install
 #+end_src

To install the package in your own user directory, you won't need root priveliges, can omit the 'sudo' command
and combine the last two commands, e.g.:
 #+begin_src bash
   mkdir build && cd build/
   cmake -DCMAKE_INSTALL_PREFIX:PATH=/home/me/usr ..
   make install
 #+end_src

To compile the code with your favourite compiler (in case you have several installed), prepend the cmake line
with e.g. ~FC=gfortran~:
 #+begin_src bash
   FC=gfortran cmake ..
 #+end_src

If you have multiple cores or processors, you can speed up the make step by specifying the number of parallel
build jobs using the -j option.  E.g., for four cores, you can have four parallel jobs and use:
 #+begin_src bash
   make -j4
 #+end_src

To compile the code without installing it anywhere, leave out the install step
 #+begin_src bash
   mkdir build && cd build/
   cmake ..
   make
 #+end_src
The compiled libraries and modules can then be found in the usr/ subdirectory of the package dir.

On a Linux system, the library and module files could be installed as:
: /usr/lib/libTheSky.*
: /usr/include/libTheSky/*.mod

If you want to use the libraries with multiple Fortran compilers, you will want to keep the different versions
of the library separated.  In this case, use (in addition to any other options):
 #+begin_src bash
   cmake -DCOMPILER_SPECIFIC_LIBS=on ..
 #+end_src
The library files will then be installed as:
: /usr/lib/libTheSky_.*
: /usr/include/libTheSky//*.mod

If one of your Fortran compilers is your default, you can use both the default installation method and the
compiler-specific method to install the library.


** Data files

The data files are distributed in a separate tarball, named ~libthesky-data-.tar.bz2~.  They will
unpack into the ~data/~ subdirectory of the package and the code will expect to find them in
~/usr/shared/libTheSky/~ by default.  Hence, to install the data files manually, do e.g.:
  #+begin_src bash
    tar xfj libthesky-data-.tar.bz2
    sudo mkdir /usr/shared/libTheSky/
    sudo cp -vi data/* /usr/shared/libTheSky/
  #+end_src

Alternatively, you can use the libTheSky_data target in the CMake file of the source code,
by copying the data files into that package's subdirectory before compiling it, and making
sure you install the data files as well:
  #+begin_src bash
    tar xfz libthesky-<0.0.1>.tar.gz
    tar xfj libthesky-data-.tar.bz2
    mv data libthesky-0.0.1/
    cd libthesky-0.0.1/
    ...
    sudo make libTheSky_data install
  #+end_src

All data files needed to use libTheSky are provided in the tarball.  The file ~asteroids.dat~ is a reduced
version of the file https://ssd.jpl.nasa.gov/dat/ELEMENTS.NUMBR.gz, containing all bodies with H<15 and a<100
AU (~25% of total, ~90,000 objects).  If you want to use the full/latest version instead, do something like:
  #+begin_src bash
  .$ wget https://ssd.jpl.nasa.gov/dat/ELEMENTS.NUMBR.gz -O - | gunzip -c > data/asteroids.dat
  #+end_src


** Contact

If you run into problems or have questions, please feel free to contact Marc van der Sluys by email through
https://marc.vandersluys.nl.



* Licence

Copyright (c) 2002-2025  Marc van der Sluys - Nikhef/Utrecht University - marc.vandersluys.nl
 
This file is part of the libTheSky package, see: https://libthesky.sf.net/

This is free software: you can redistribute it and/or modify it under the terms of the European Union Public
Licence 1.2 (EUPL 1.2).  This software is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
EU Public Licence for more details.  You should have received a copy of the European Union Public Licence
along with this code.  If not, see .

Owner

Citation (CITATION.cff)

cff-version: 1.1.0
message: "Please cite the following works when using this software: https://ui.adsabs.harvard.edu/abs/2022ascl.soft09018V"
authors:
- family-names: van der Sluys
  given-names: Marc
title: "libTheSky: Compute positions of celestial bodies and events"
version: 0.4.2
date-released: 2021-08-22
identifiers:
 - type: "ascl-id"
   value: "2209.018"
 - type: "bibcode"
   value: "2022ascl.soft09018V"
abstract: "libTheSky computes the positions of celestial bodies, such as the Moon, planets, and stars, and events, including conjunctions and eclipses, with great accuracy. Written in Fortran, libTheSky can use different reference frames (heliocentric, geocentric, topocentric) and coordinate systems (ecliptic, equatorial, galactic; spherical, rectangular), and the user can choose low- or high-accuracy calculations, depending on need."

CodeMeta (codemeta.json)

{
  "@context": "https://doi.org/10.5063/schema/codemeta-2.0",
  "@type": "SoftwareSourceCode",
  "name": "libTheSky: Compute positions of celestial bodies and events",
  "description": "libTheSky computes the positions of celestial bodies, such as the Moon, planets, and stars, and events, including conjunctions and eclipses, with great accuracy. Written in Fortran, libTheSky can use different reference frames (heliocentric, geocentric, topocentric) and coordinate systems (ecliptic, equatorial, galactic; spherical, rectangular), and the user can choose low- or high-accuracy calculations, depending on need.",
  "identifier": "ascl:2209.018",
  "author": [
    {
      "@type": "Person",
      "givenName": "Marc",
      "familyName": "van der Sluys",
      "@id": "https://orcid.org/0000-0003-1231-0762"
    }
  ],
  "citation": "https://ui.adsabs.harvard.edu/abs/2022ascl.soft09018V",
  "relatedLink": [
    "https://libthesky.sourceforge.net/"
  ],
  "codeRepository": [
    "https://sourceforge.net/projects/libthesky/",
    "https://github.com/MarcvdSluys/libTheSky"
  ],
  "version": "0.4.3",
  "license": "https://spdx.org/licenses/EUPL-1.2.html"
}

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