Irish (Gaeilge), also referred to as Gaelic or Irish Gaelic, is a Goidelic language of the Indo-European language family originating in Ireland and historically spoken by the Irish people. Irish is spoken as a first language by a small minority of Irish people, and as a second language by a rather larger group of non-native speakers. Irish enjoys constitutional status as the national and first official language of the Republic of Ireland, and is an officially recognised minority language in Northern Ireland. It is also among the official languages of the European Union. The public body Foras na...

The solar luminosity, L☉, is a unit of radiant flux (power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars. It is defined in terms of the Sun's output. One solar luminosity is 7026382800000000000♠3.828×1026 W. This does not include the solar neutrino luminosity, which would add 0.023 L☉. The Sun is a weakly variable star, and its luminosity therefore fluctuates. The major fluctuation is the eleven-year solar cycle (sunspot cycle) that causes a periodic variation of about ±0.1%. Other variations over the last 200–300 years are thought to be much...

Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. The term is derived from the Greek word παράλλαξις (parallaxis), meaning "alternation". Due to foreshortening, nearby objects have a larger parallax than more distant objects when observed from different positions, so parallax can be used to determine distances. Astronomers use the principle of parallax to measure distances to the closer stars. Here, the term "parallax" is the semi-angle o...