# Rektaszension

in the astronomy is Rektaszension (the term used in old German books originates from latin and reads “straight ascending”) the correspondence of the geographical length circles on (imaginary) the sky ball. As zero point of the Rektaszension thereby the Frühlingspunkt serves.The Rektaszension, which is used with the position indication by celestial objects, is measured regarded from the north in against clockwise direction.

In the astronomy it became generally accepted, the Rektaszension not in degrees to indicate but in the time measure in hours whereby 24h = 360° to be set. It applies:

Rektaszension angle
1 hour of 15°
1 minute 15 ' (Bogenminuten) = 1/4°
1 second 15 " (Bogensekunden) = 1/240°

as contractions becomes RA (English. Right Ascension) uses, whereby the GreekLetter α the angle between the degree of longitude of the Frühlingspunkts up to the degree of longitude over that the observed object stands, defined (measured on the equatorial plane).

RA and/or. α the most common abbreviation for Rektaszension is - that celestial coordinate which is certain in the area,to the geographical length on rotary earth corresponds.

It counts its Nullmeridian along the celestial equator and is defined by the Frühlingspunkt, the intersection between ecliptic ( plane of the Earth's orbit ) and equator, directed to the north.
The second coordinate (δ) is called declination.

RA and δ can be converted by means of the ecliptic-inclined ε into the ekliptikale length λ and width β - see small triangle right on the sketch. This Koordinatentransformation is for the computation of the orbits of planets and other bodythe solar system essential.

The interested one can measure with well-known Rektaszension of a star or other astronomical objects easily, at which time in the year the object at the best one is to be observed, by measuring the date computed/, to its highest collection overthe horizon in for instance on midnight falls (opposition). The Trifidnebel e.g. a declination of approx. -22° has and is only difficult therefore in our widths to observe (highest level only approximately 15°). If one the Rektaszension of the fog ofapprox. 18h to the 12 months of the yearly refers, receives one 9 months. Outgoing from the Frühlingspunkt such a date results around the 21. December. That is the time, where the highest collection falls on noon, therefore lies the optimalVisibility 6 months before it and/or. afterwards and falls therefore in the example mentioned in for instance on the 21. June.