Free software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, not price; all users are legally free to do what they want with their copies of a free software regardless of how much is paid to obtain the program. Computer programs are deemed "free" if they give end-users ultimate control over the software and, subsequently, over their devices.
LaTeX is a software system for document preparation. When writing, the writer uses plain text as opposed to the formatted text found in "What You See Is What You Get" word processors like Microsoft Word, LibreOffice Writer and Apple Pages. The writer uses markup tagging conventions to define the general structure of a document to stylise text throughout a document, and to add citations and cross-references. A TeX distribution such as TeX Live or MiKTeX is used to produce an output file suitable for printing or digital distribution.
gnuplot is a command-line and GUI program that can generate two- and three-dimensional plots of functions, data, and data fits. The program runs on all major computers and operating systems . It is a program with a fairly long history, dating back to 1986. Despite its name, this software is not part of the GNU Project.
KStars is a freely licensed planetarium program using the KDE Platform. It is available for Linux, BSD, macOS, and Microsoft Windows. A light version of KStars is available for Android devices. It provides an accurate graphical representation of the night sky, from any location on Earth, at any date and time. The display includes up to 100 million stars, 13,000 deep sky objects, constellations from different cultures, all 8 planets, the Sun and Moon, and thousands of comets, asteroids, satellites, and supernovae. It has features to appeal to users of all levels, from informative hypertext articles about astronomy, to robust control of telescopes and CCD cameras, and logging of observations of specific objects.
In cartography, map projection is the term used to describe a broad set of transformations employed to represent the two-dimensional curved surface of a globe on a plane. In a map projection, coordinates, often expressed as latitude and longitude, of locations from the surface of the globe are transformed to coordinates on a plane. Projection is a necessary step in creating a two-dimensional map and is one of the essential elements of cartography.
The LaTeX Project Public License (LPPL) is a software license originally written for the LaTeX system. Software distributed under the terms of the LPPL can be regarded as free software; however, it is not copylefted.
In astronomy, a planisphere is a star chart analog computing instrument in the form of two adjustable disks that rotate on a common pivot. It can be adjusted to display the visible stars for any time and date. It is an instrument to assist in learning how to recognize stars and constellations. The astrolabe, an instrument that has its origins in Hellenistic astronomy, is a predecessor of the modern planisphere. The term planisphere contrasts with armillary sphere, where the celestial sphere is represented by a three-dimensional framework of rings.
Stellarium is a free and open-source planetarium, licensed under the terms of the GNU General Public License version 2, available for Linux, Windows, and macOS. A port of Stellarium called Stellarium Mobile is available for Android, iOS, and Symbian as a paid version, being developed by Noctua Software. All versions use OpenGL to render a realistic projection of the night sky in real time.
IRAF is a collection of software written at the National Optical Astronomy Observatory (NOAO) geared towards the reduction of astronomical images in pixel array form. This is primarily data taken from imaging array detectors such as CCDs. It is available for all major operating systems for mainframes and desktop computers. Although written for UNIX-like operating systems, use on Microsoft Windows is made possible by Cygwin. It is primarily used on Linux distributions, with a growing share of Mac OS X users. IRAF is installed by default in Distro Astro, a Linux distribution for astronomers.
The azimuthal equidistant projection is an azimuthal map projection. It has the useful properties that all points on the map are at proportionally correct distances from the center point, and that all points on the map are at the correct azimuth (direction) from the center point. A useful application for this type of projection is a polar projection which shows all meridians as straight, with distances from the pole represented correctly. The flag of the United Nations contains an example of a polar azimuthal equidistant projection.
Lout is a batch document formatter invented by Jeffrey H. Kingston. It reads a high-level description of a document similar in style to LaTeX and produces a PostScript file which can be printed on most printers. Plain text and PDF output are also available. The term Lout primarily designates a document formatting programming language, while the (only) implementation of the language is sometimes referred to as Basser Lout. Basser Lout is free software, distributed under the terms of the GNU General Public License.
HNSKY or Hallo Northern Sky is a popular free and open-source planetarium program for Linux, macOS, Microsoft Windows, and Raspberry Pi to simulate the night sky. It is provided with several non-English language modules, numerous astronomical catalogues, conversion utilities and tools, as well as several stellar databases.
Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) is a molecular dynamics program from Sandia National Laboratories. LAMMPS makes use of Message Passing Interface (MPI) for parallel communication and is free and open-source software, distributed under the terms of the GNU General Public License.
Cartes du Ciel is a free and open source planetarium program for Linux, macOS, and Windows. With the change to version 3, Linux has been added as a target platform, licensing has changed from freeware to GPLv2 and the project moved to a new website.
The Aitoff projection is a modified azimuthal map projection proposed by David A. Aitoff in 1889. Based on the equatorial form of the azimuthal equidistant projection, Aitoff first halves longitudes, then projects according to the azimuthal equidistant, and then stretches the result horizontally into a 2:1 ellipse to compensate for having halved the longitudes. Expressed simply:
The General Perspective projection is a map projection. When the Earth is photographed from space, the camera records the view as a perspective projection. When the camera is aimed toward the center of the Earth, the resulting projection is called Vertical Perspective. When aimed in other directions, the resulting projection is called a Tilted Perspective.
The GNU General Public License is a series of widely used free software licenses that guarantee end users the four freedoms to run, study, share, and modify the software. The license was the first copyleft for general use and were originally written by the founder of the Free Software Foundation (FSF), Richard Stallman, for the GNU Project. The license grant the recipients of a computer program the rights of the Free Software Definition. These GPL series are all copyleft licenses, which means that any derivative work must be distributed under the same or equivalent license terms. It is more restrictive than the Lesser General Public License and even further distinct from the more widely used permissive software licenses BSD, MIT, and Apache.
Digital Universe Atlas is a free open source software planetarium application, available under the terms of the Illinois Open Source License, and running on Linux, Windows, macOS, AmigaOS 4, and IRIX.
Amateur flight simulation refers to the simulation of various aspects of flight or the flight environment for purposes other than flight training or aircraft development. A significant community of simulation enthusiasts is supported by several commercial software packages, as well as commercial and homebuilt hardware. Open-source software that is used by the Aerospace industry like FlightGear, whose flight dynamics engine (JSBSim) is used in a 2015 NASA benchmark to judge new simulation code to space industry standards, is also available for amateur use. A popular type of amateur flight simulators are combat flight simulators, which simulate combat air operations from the pilot and crew's point of view. Combat flight simulation titles are more numerous than civilian flight simulators due to variety of subject matter available and market demand.
