constellation
In visual astronomy and astronomical phenomenology, the constellation is the apparent position of bright celestial bodies relative to one another, as it appears from the position of an observer on earth. The term is used to this day in both astronomy and space travel as well as astrology .
etymology
The term is composed of the Latin parts of the word stella ("star") and the prefix con ("together"), freely translated as "meeting of stars". Its original meaning goes back to astrology (see below - sections Constellations of ... ) and is here synonymous with the Greek word ancient Greek ἐποχή (epochḗ) "breakpoint". It means "holding on" or the "stopping point" of the image of a temporary meeting of celestial bodies.
astronomy
These are apparent views of the sky for the location ( reference system ) of the observer. As the position of the planet , position of the moon, etc., they relate to a coordinate system on the fixed star sky or to the position of the celestial bodies in relation to one another ( aspect , Latin: aspectus = sight, view).
Special constellations ( main positions ) have their own names, whereby - in astrometry ("star measurement") or as astronomical events in the ephemeris calculation ("astronomical diary") - they are still used today according to the historical terms " wandering stars " ( planets , planetoids , moons ) as well as " fixed stars " ("real" stars ).
The term primarily describes the special angular positions of the large planets relative to the sun (conjunction, opposition, etc.), but also of the earth's moon to the sun and earth, analogous to the moons of the other planets, and the position of celestial bodies to celestial mechanical reference points such as the equinox , periapsis or celestial pole , sometimes also encounters with bright fixed stars ,
Constellations in the broader sense concern relative star locations ( star constellations ), in particular the constellations .
Constellations of "wandering stars" (planets, moons, comets, etc.)
The most common of these constellations relate to the angle between the object and the sun that is visible from Earth . It is called elongation and is the difference between the ecliptical lengths of the sun and the object:
- Opposition ("facing") of a celestial body: elongation 180 °
- Conjunction ("encounter"): elongation 0 °
- Quadrature ("crossing" or "square"): Elongation 90 °
- In astrology also sextile and trine of planets: mutual angular distance 60 ° or 120 °
- Half phase (dichotomy “separation in two halves”): a phase angle of 90 °
- the greatest or smallest elongation in the inner planets
- Planetary row or alignment - along the ecliptic , or with other stars or the moon in relation to the horizon
- Passage ( passage , transit , eclipse / occultation , covering , close encounters ), various events that relate to a small angle difference between two objects.
Constellations of "fixed stars"
Apparent star clusters
So-called asterisms without physical (gravitational) connection:
- the 88 constellations that the International Astronomical Union (IAU) has set as the standard for sky mapping
- historical constellations of western astronomy
- Constellations in other cultures (Sumerians, Ancient China , India, Mayans , etc.)
- bright groups of stars - especially with a conspicuous shape such as B. Star rows : they are mostly only apparent clusters, whereby the stars can have very different distances.
True star clusters
Star groups and clusters whose members are spatially closely spaced:
- Open star clusters : stars formed at the same time that still form a loose group of 20–200 suns - e. B. Pleiades (seven stars) and Hyades in Taurus, Praesepe in Cancer, etc.
- Close star groups in star clusters: Trapeze of the Pleiades , bull head of the Hyades, star chains in nearby star clusters such as Messier 36
- Globular clusters : very compact "nebulae" with 50,000–500,000 stars, which can only be resolved into individual stars in the telescope at the edge
-
Galaxies :
- the Milky Way and its nearby spiral arms , the brightest star as part of some constellations or star clouds may appear
- nearby spiral nebulae , of which individual giant stars can be seen in large telescopes
- Groups of galaxies ( clusters of galaxies ) and the large structures of the universe: they cannot be seen with open eyes and are therefore rarely referred to as a constellation.
In practice, because of the difficulties in measuring fixed stars at great distances, it is not always possible to establish with certainty whether a grouping of fixed stars is an apparent or a real cluster.
Individual evidence
- ↑ έποχή . In: Gustav Eduard Benseler et al .: Greek-German school dictionary . 13th edition. BG Teubner, Leipzig 1911, p. 341
- ↑ Aspects (lexicon entry). In: Meyers Großes Konversations-Lexikon. 6th edition, Bibliographisches Institut, Leipzig / Vienna 1905–1909. 1909, Retrieved July 23, 2018 .
- ↑ Albrecht Unsöld : The new cosmos . Springer-Verlag, Berlin 1967 and 2005