Heliacisch
Heliakisch (also " Morgenerst " and " Morgenletzt ") is a generic term in astronomy and means " belonging to the rising sun ". The term is used in connection with the culmination as well as the rising and setting of celestial bodies at dawn , especially with regard to stars , planets and the moon . The terms “ morning first ” and “morning last”, which have been used since antiquity and are synonymous with “heliacal”, are mainly used in astrology .
The apparent brightness of the celestial bodies and the respective duration of twilight determine on which day a celestial body rising in the east or a celestial body setting in the west can be seen with the naked eye at dawn for the last time. The opposite term, related to dusk, is acronymic (also “evening first” and “evening last”).
Heliac rising and setting as well as heliac culmination
Since the earth orbits the sun once a year , the sun moves once a year on the ecliptic through the starry sky when viewed from the earth . The stars rise (/ set) earlier than the sun about four minutes earlier each day. Their heliacal emergence over the horizon is not visible to the naked eye until a few days after the passage at dawn. The star then rises earlier than the sun. The sky is not yet outshone by sunlight.
Meaning in ancient Egypt
The heliacal rise of Sirius in ancient Egypt as the bringer of the flood of the Nile was particularly important . Both events occurred from around 2000 BC. Together. Before that, the heliacal rise of Sirius was too early for the Nile flood due to the precession of the earth. For the Egyptians, the irrigation and supply of the Nile mud, which are important for cultivation and sowing, began with the Nile flood . The New Year festival was also coupled with the heliacal rise of Sirius (see Sothis cycle ). In Sumer , Assyria and Babylonia some stars took on important functions as signal transmitters for the agricultural calendar with their heliacal rise.
A star that is nearly in opposition to the sun sets heliacally just before it rises. These events did not acquire the same significance in chronology as the morning stars visible for the first time in the east (heliacal rise). The upper heliacal culmination refers to the time at dawn at which a star in its daily movement reaches the greatest height above the horizon or at the lower culmination the smallest height. In ancient Egyptian astronomy , great importance was attached to the upper heliacal culminations of the Dean stars (see Naos of the Decades ).
Heliacal rises of Venus in the morning sky
The apparent relative movement between the sun and the planets is only similar to the stars in the case of the upper planets (but retrograde movement / planetary loop when these are in opposition to the sun). The conditions of the lower planets Mercury and Venus are completely different , of which the heliacal events of Venus are the more important because of their great brightness.
Unlike the stars and planets above, Venus (and Mercury) are not periodically overtaken by the sun in the sky. It can be seen alternately in the morning and evening sky for a maximum of about four hours, but never in the middle of the night, because it cannot be in opposition to the sun.
Your visibility as a morning star is limited by two heliacal ascents, one visible for the first time and one for the last time. In the case of the stars, there is only ever one rise visible for the first time in a year.
Heliacal setting of the moon in the morning sky
Just as the sun overtakes the stars once a year, the moon overtakes it once a month . This means that the moon rises later than the sun after it has overtaken it. Shortly before hauling in, you can see it rise for the last time at dawn (“morning last”) in the east. The moon does not have a “morning first”, since it never rises heliacally, but acronychically (“evening first”).
Heliac year
The period of time between two consecutive heliacal rises of a star is known as the heliacal year . The length and the beginning of such a year depends on the geographical latitude and the position of the star. The longitude corresponds to a tropical year only if the star has the ecliptical latitude of 0 °.
See also
- Cosmic rise
- Priest astronomers in Mesopotamia
- Morning sky
- Morning distance
literature
- Susanne Dennigmann: The Astrological Doctrine of Doryphoria: A Sociomorphic Metaphor in Ancient Planetary Astrology. Saur, Munich 2005, ISBN 3-5987-7826-0 .
- Alexandra von Lieven : Floor plan of the course of the stars - the so-called groove book. The Carsten Niebuhr Institute of Ancient Eastern Studies, Copenhagen 2007, ISBN 978-87-635-0406-5 .