Sun apex
The sun apex (Latin apex = “tip”, “dome”, “helmet”) is the vanishing point of the movement of our sun compared to the mean of the neighboring bright stars , ie relative to the (fictitious) local rest system . This point is in the constellation Hercules , southwest of the Vega . The opposite direction is called the antapex and lies in the constellation Dove .
history
The first determination of the apex was carried out by Wilhelm Herschel in 1783 . From 1822 Carl Friedrich Gauß also calculated the sun apex using very different methods, but never published the calculations himself. The first precise determination was published by Friedrich Wilhelm August Argelander in his treatise On the Movement of the Solar System (1837). His result agreed pretty well with Herschel's. Later the main method was rediscovered independently by Auguste Bravais and George Biddell Airy .
It was only after 1900 that it became clear that a major difficulty in determining the apex of the sun's motion was based on the anisotropic velocity distribution of the stars.
According to current values from the beginning of the 21st century, the sun moves relative to the local rest system at 19.7 km / s in the direction of the apex, which according to the galactic coordinate system is at a galactic longitude of 57 ° and a galactic latitude of 22 °. This corresponds in equatorial coordinates as RA = 18 h and DEC = 30 °.
meaning
The apex movement must be taken into account when evaluating speed measurements in the Milky Way in order to be able to draw conclusions about the actual galactic movements from the relative speed to the sun.
Earth apex
Based on the sun apex, especially in meteor observations, the vanishing point of the earth's movement relative to the sun - i.e. the direction in which the earth moves at around 30 km / s - is called the earth apex . This direction is tangential to the earth's orbit , so it is at right angles to the earth-sun line. Therefore, the earth apex in the starry sky is offset by approx. 90 ° to the position of the sun and moves along the ecliptic over the course of a year . It is particularly high in the sky in the early morning hours, which is why you can often count more meteors in the second half of the night than in the first.
See also
literature
- Arnold Hanslmeier : Introduction to Astronomy and Astrophysics . Spektrum Akademischer Verlag, 2nd edition 2007, ISBN 978-3-8274-1846-3 , p. 414.
- Joachim Krautter et al .: Meyers Handbuch Weltall . Meyers Lexikonverlag, 7th edition 1994, ISBN 3-411-07757-3 , p. 242.