Heliacal rising

The heliacal rising (/hɪˈlaɪ.əkəl/ hih-LY-ə-kəl)^[1]^[2]^[3] of a star or a planet occurs annually when it first becomes visible above the eastern horizon at dawn just before sunrise (thus becoming "the morning star") after a complete orbit of the Earth around the Sun.^[4] Historically, the most important such rising is that of Sirius, which was an important feature of the Egyptian calendar and astronomical development. The rising of the Pleiades heralded the start of the Ancient Greek sailing season, using celestial navigation,^[5] as well as the farming season (attested by Hesiod in his Works and Days). Helical rising is one of several types of risings and settings, mostly they are grouped into morning and evening risings and settings of objects in the sky. Culmination in the evening and then morning is set apart by half a year, while on the other hand risings and settings in the evenings and the mornings are only at the equator set apart by half a year.

^ "heliacal". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
^ "heliacal". Merriam-Webster.com Dictionary.
^ "heliacal". Dictionary.com Unabridged (Online). n.d.
^ "Show Me a Dawn, or "Heliacal," Rising". Stanford University. Heliacal risings occur after a star has been behind the Sun for a season and it is just returning to visibility. There is one morning, just before dawn, when the star suddenly reappears after its absence. On that day it "blinks" on for a moment just before the sunrise and just before it is then obliterated by the Sun's presence. That one special morning is called the star's heliacal rising.
^ "Pleiad". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)

[OED-1] "heliacal". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)

[2] "heliacal". Merriam-Webster.com Dictionary.

[3] "heliacal". Dictionary.com Unabridged (Online). n.d.

[4] "Show Me a Dawn, or "Heliacal," Rising". Stanford University. Heliacal risings occur after a star has been behind the Sun for a season and it is just returning to visibility. There is one morning, just before dawn, when the star suddenly reappears after its absence. On that day it "blinks" on for a moment just before the sunrise and just before it is then obliterated by the Sun's presence. That one special morning is called the star's heliacal rising.

[5] "Pleiad". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)

[1]

[2]

[3]

[4]

[5]