Acronic is a synonym of atemporal. Heliacal, from greek Ήλιος, or Sun, rising and setting of a star to signify the exit or entry of it in the rays of sun that prevents the observation. The rising and setting of a star are nothing more than an appearance or disappearance. So we have:
- Acronic rising: is the rise of a star on the eastern horizon at the same time as the Sun sets.
- Acronic Sunset : is the set of a star in the western horizon at the same time than the Sun rising. During its acronic set a star is always invisible, because of the sunlight.
- Heliacal rising: it is the becoming visible of a star in contrast to the light of the Sun.
- Heliacal morning rising : the first appearance of a star on the eastern horizon before dawn.
- Heliacal Vespers rising is the first visibility of Venus or Mercury in the western horizon after the Sun sunset.
- Heliacal Sunset: is the becoming invisible of a star because of its proximity to the Sun.
- Heliacal morning Sunset: it is the last visibility of Venus or Mercury in the eastern horizon, before dawn.
- Heliacal Sunset Vespers: is the last visibility of a star in the western horizon, after the Sun sunset.
The heliacal phenomena are an integral part of the rhythm of the sky, so many ancient cultures, by which the observation of the sky was widely practiced, included them in the list of celestial phenomena considered important and, as such, worthy of careful and continuous observation and recording, mainly because of their high temporal resolution. In the majority of cases the heliacal phenomena had to do with the development of the first calendars with the cadence of the rituals along the year. The observation of the sequence of the heliacal risings that were visible in a certain place, allowed the easy and unambiguous delineation of a series of well-defined dates during the year. Virtually all the ancient people of which we have written documentation relative to their customs and traditions, used this method to define with reasonable accuracy the key dates relevant to agricultural planning and navigation, just remember the greek Hesiod and his work ” Works and Days”.
Often, concurrently at the time of the heliacal rising of a particular star, was celebrated a festival which was generally associated, in terms of ritual, to both the astronomical event that determined the occurrence, and the social event that should be celebrated. We know for certain, from the available documents, that in ancient Egypt the heliacal risings of Sirius were currently observed and established the beginning of the Egyptian agricultural calendar. The heliacal rising of Sirius preluded to beneficial flooding of the Nile, which was crucial for the agricultural economy of the people. The Maya divided their ritual calendar in four segments on the basis of the dates of heliacal rising of the planet Venus, a phenomenon currently observed even at Babylon and which we have accurate records in cuneiform on clay tablets, in India and China. The Babylonians did start the year with the heliacal rising of Hamal (Alpha Arietis). Also the Celts in Europe used to set the basis of the four key festivals of the Celtic year basing them on the dates of heliacal rising of the stars (3).
Four, out of the eight spokes of the time wheel, were surely solstices and equinoxes. The remaining four should not be taken for granted. Calendars, or means to calculate the right time, have always been substantial (4). This is known as ” Signatures”, which is not only an issue of “weights”, but also of external conditions.
Other articles on the Wheel allegory: Amiens Cathedral, Fulcanelli and Two Paradoxical Wheels , Heiligen Dreifaltigkeit and Secret Iconography of the Wheel .
The picture at the top of the first page has been taken from www.angolohermes.com .
- Nicola Severino “Antologia Di Storia Della Gnomonica”, Roccasecca 1995 ;
- See also Two Stars in a Venetian Geocentric Sky ;
- Cernuti S., Gaspani A., 2006, “Introduzione All’Archeoastronomia: Nuove Tecniche Di Analisi Dei Dati”, Atti della Fondazione Giorgio Ronchi, vol. LXXXIX, 190 pp. Edizioni Tassinari, Firenze, 2006. A. Gaspani, 2000, “Archeoastronomia, Astroarcheologia, Paleoastronomia”, Ad Quintum, No.6, Novembre 2000 ;
- See also San Miniato Sun Path or the Sky as Seen from Earth , Thesaurus Hermeticum & Dry Pythagorean River , Nuisement and the Sun Resisting Capture , Voynich Manuscript and the Unknown Part of the Rhythm , Pietro Perugino and the Lady of the Wind , Santi Pupieni and the Raising Black-New Moon ;