Parsec

A parsec (symbol: pc) is a unit of length used to measure large distances to objects outside the Solar System. One parsec is the distance at which one astronomical unit subtends an angle of one arcsecond. A parsec is equal to about 3.26 light-years (31 trillion kilometres or 19 trillion miles) in length. The nearest star, Proxima Centauri, is about 1.3 parsecs from the Sun. Most of the stars visible to the unaided eye in the nighttime sky are within 500 parsecs of the Sun.

The parsec unit was likely first suggested in 1913 by British astronomer Herbert Hall Turner. Named from an abbreviation of the parallax of one arcsecond, it was defined so as to make calculations of astronomical distances quick and easy for astronomers from only their raw observational data. Partly for this reason, it is still the unit preferred in astronomy and astrophysics, though the light year remains prominent in popular science texts and everyday usage. Although parsecs are used for the shorter distances within the Milky Way, multiples of parsecs are required for the larger scales in the universe, including kiloparsecs for the more distant objects within and around the Milky Way, megaparsecs for all but the closest galaxies, and gigaparsecs for many quasars and the most distant galaxies.

Parsec (video game)

Parsec is a computer game for the Texas Instruments TI-99/4A. Perhaps the best-remembered of all TI-99/4A games, it is a side-scrolling shooter, programmed in 1982 by Jim Dramis (who also programmed the popular TI-99/4A games Car Wars and Munch Man) and Paul Urbanus.

Object

The player in Parsec pilots a spaceship through sixteen differently-colored levels of play which scroll horizontally over the screen. The objective is to avoid being shot by an enemy ship or colliding with any flying object. All ships must be shot.

Gameplay

Three waves of fighters attack, alternating with three waves of cruisers. Enemy ships enter the screen one at a time. A ship flying off the left edge of the screen wraps around to the right side and attacks again. A new fighter can appear with others still on the screen, whereas a new cruiser will not come until the previous one is destroyed. The fighters pose only the threat of collision, while the cruisers fire on the player's ship. The fighter types are named Swoopers, LTFs (Light Triangular Fighters), and Saucers. The cruisers are called Urbites, Dramites, and Bynites. Each level ends with an asteroid belt, in which columns of asteroids advance on the ship and must be avoided or shot. At the end of each asteroid belt, any remaining asteroids are cleared away and the color of the ground is changed, then a new wave of Swoopers begins. Starting with level 4, the Swoopers are preceded by a random number of Killer Satellites, which come without the usual computer warning.

Parsec (parser)

Parsec is a library for writing parsers in Haskell. It is based on higher-order parser combinators, so a complicated parser can be made out of many smaller ones. It has been reimplemented in many other languages, including Erlang, OCaml, F# and C#, as well as imperative languages such as Java.

Because a parser combinator-based program is generally slower than a parser generator-based program, Parsec is normally used for small domain-specific languages, while Happy is used for compilers such as GHC.

References

External links

Parsec (disambiguation)

A parsec is a unit of distance.

Parsec may also refer to:

See also

List of minor planets: 30001–31000

PARSEC

PARSEC is a package designed to perform electronic structure calculations of solids and molecules using density functional theory (DFT). The acronym stands for Pseudopotential Algorithm for Real-Space Electronic Calculations. It solves the Kohn–Sham equations in real space, without the use of explicit basis sets.

One of the strengths of this code is that it handles non-periodic boundary conditions in a natural way, without the use of super-cells, but can equally well handle periodic and partially periodic boundary conditions. Another key strength is that it is readily amenable to efficient massive parallelization, making it highly effective for very large systems.

Its development started in early 1990s with James Chelikowsky (now at the University of Texas), Yousef Saad and collaborators at the University of Minnesota. The code is freely available under the GNU GPLv2. Currently, its public version is 1.3.6. Some of the physical/chemical properties calculated by this code are: Kohn–Sham band structure, atomic forces (including molecular dynamics capabilities), static susceptibility, magnetic dipole moment, and many additional molecular and solid state properties.