Right ascension
Right ascension (Latin ascensio recta = straight ascent) is one of the two polar coordinates in the so-called rotating equatorial coordinate system of spherical astronomy. Whose second coordinate is the declination.
It is calculated on the celestial equator angle between the vernal equinox and the length circle on which the observed celestial body is, and is the analogue of the globe relating to the longitude. The most common abbreviations are α or a
The right ascension is often specified in the measure of time than in degrees or radians. The information in the time scale refers to the fact that the apparent rotation of the stars around the earth at the time is proportional and time differences can be determined relatively easily.
Word meaning and measure of time
The word ascension right ascension is the combination of letters recta, the reverse order of the Latin ascensio recta. In English, the term is right ascension ( common abbreviation RA) as literal translation of the old Latin term used. In the older German literature the literal translation was also used from the Latin, namely a straight climb or Geradeaufsteigung ..
Ascensio recta refers to as the rise ( ascensio, ascension or ascent) takes place a star on the horizon in the Earth's equator, namely perpendicular ( recta, right or straight) to the horizon. At the moment of the star Aufgangs its meridian coincides with the horizon circle. The east point of the horizon is the intersection of the meridian with the there vertical celestial equator and hence the current point to the right ascension of the star to be measured.
When a star at the equator rises a star - hour after the vernal equinox, so it has the right ascension 15 ° ( the stars move in a star - day to 24 -hour star seemingly on a full circle of 360 °).
Equatorial coordinate system
The zero point of right ascension of the vernal equinox is. It grows as the longitude east.
In celestial navigation and the widening westward star angle (English sidereal hour angle (SHA ) ) is used instead of the right ascension.
In the fixed equatorial coordinate system of the hour angle is used instead of the right ascension.
Right ascension α and declination δ correspond in the ecliptic coordinate system ecliptic longitude λ and β the ecliptic latitude. To convert the obliquity ε is used, see small triangle to the right of the sketch. This coordinate transformation is essential for calculating the orbits of planets and other bodies in the solar system.