Editing Heliacal rising (section)

== History ==
Constellations containing stars that rise and set were incorporated into early [[calendar]]s or [[zodiac]]s. The [[Sumer]]ians, [[Babylonia]]ns, [[ancient Egyptians|Egyptians]], and [[Ancient Greece|Greeks]] all used the heliacal risings of various stars for the timing of agricultural activities.

Because of its position about 40° off the ecliptic, the heliacal risings of the bright star [[Sirius]] in [[Ancient Egypt]] occurred not over a period of exactly one [[sidereal year]] but over a period called the "[[Sothic year]]" (from "Sothis", the name for the star Sirius). The Sothic year was about a minute longer than a [[Julian year (calendar)|Julian year]] of 365.25 days.<ref name=teacosy>{{harvp|Tetley|2014|p=[https://web.archive.org/web/20171114202029/http://www.egyptchronology.com/uploads/2/6/9/4/26943741/ch_3_investigating_ancient_egyptian_calendars.pdf 42]}}.</ref> Since the development of [[civilization]], this has occurred at [[Cairo]] approximately on July 19 on the [[Julian calendar]].<ref name=lavia>{{citation |contribution-url =https://web.archive.org/web/20131225071503/https://www.lavia.org/english/archivo/egyptiancalendaren.html|contribution=Ancient Egyptian Civil Calendar |title = La Via |url = http://www.lavia.org/indexIT.html |access-date=8 February 2017 }}.</ref>{{efn|The exact date varies with [[latitude]], so that Sirius's return is observed about 8–10 days later on the [[Mediterranean Sea|Mediterranean]] coast than at [[Elephantine|Aswan]].<ref name=teatime>{{citation |last=Tetley |first = M. Christine |title = The Reconstructed Chronology of the Egyptian Kings, ''Vol. I'' |url = http://www.egyptchronology.com/vols-1--2.html |year = 2014 |page = [http://www.egyptchronology.com/uploads/2/6/9/4/26943741/ch_3_investigating_ancient_egyptian_calendars.pdf 43] |access-date=2017-02-09 |archive-url = https://web.archive.org/web/20170211075421/http://www.egyptchronology.com/vols-1--2.html |archive-date=2017-02-11 |url-status=dead }}.</ref> Official observations were made at [[Heliopolis (ancient Egypt)|Heliopolis]] or [[Memphis, Egypt|Memphis]] near [[Cairo]], [[Thebes, Egypt|Thebes]], and [[Elephantine]] near [[Aswan]].<ref name=teatime/> The date at any location also slowly varies within the [[Gregorian calendar]] by about three days every four centuries. July 19 of the Julian Calendar occurs on August 1 Gregorian in the 20th and 21st centuries.}} Its returns also roughly corresponded to the onset of the [[flooding of the Nile|annual flooding]] of the [[Nile]], although the flooding is based on the tropical year and so would occur about three quarters of a day earlier per century in the Julian or Sothic year. (July 19, 1000&nbsp;BC in the Julian Calendar is July 10 in the [[proleptic Gregorian Calendar]]. At that time, the sun would be somewhere near [[Regulus]] in [[Leo (constellation)|Leo]], where it is around August 21 in the 2020s.) The ancient Egyptians appear to have constructed their 365-day [[Egyptian calendar|civil calendar]] at a time when [[Wep Renpet (month)|Wep Renpet]], its [[New Year]], corresponded with Sirius's return to the night sky.<ref name=teacosy/> Although this calendar's lack of [[leap year]]s caused the event to shift one day every four years or so, [[Egyptian astronomy|astronomical records]] of this displacement led to the discovery of the [[Sothic cycle]] and, later, the establishment of the more accurate [[Julian calendar|Julian]] and [[Alexandrian calendar]]s.

The Egyptians also devised a method of telling the time at night based on the heliacal risings of 36 [[Decans|decan stars]], one for each 10° segment of the 360° circle of the zodiac and corresponding to the ten-day "weeks" of their civil calendar.

To the [[Māori people|Māori]] of [[New Zealand]], the [[Pleiades]] are called [[Matariki]], and their heliacal rising signifies the beginning of the new year (around June). The [[Mapuche]] of [[South America]] called the Pleiades ''Ngauponi'' which in the vicinity of the ''[[we tripantu]]'' (Mapuche new year) will disappear by the west, ''lafkenmapu'' or ''ngulumapu'', appearing at dawn to the East, a few days before the birth of new life in nature. Heliacal rising of Ngauponi, i.e. appearance of the Pleiades by the horizon over an hour before the sun approximately 12 days before the winter solstice, announced ''we tripantu''.

When a planet has a heliacal rising, there is a [[Conjunction (astronomy)|conjunction]] with the sun beforehand. Depending on the type of conjunction, there may be a [[Syzygy (astronomy)|syzygy]], [[eclipse]], [[Transit (astronomy)|transit]], or [[occultation]] of the sun.