Heliacal Rising of Sothis (prt Spdt)

pret SOP-det

egyptian: prt Spdt · greek: Σῶθις

Definition

The heliacal rising of Sothis is the morning when the star Sirius (Egyptian Sopdet, Greek Sothis) first reappears low in the eastern sky just before sunrise, after roughly seventy days lost in the Sun's glare. The Egyptians called it prt Spdt, "the going-forth of Sothis." A heliacal rising is simply a star's first pre-dawn comeback after a spell of invisibility. This particular dawn was the most watched-for event in the Egyptian sky: it heralded both the New Year and the start of the yearly Nile flood.

In Tradition

Egyptologists treat prt Spdt as the single astronomical event that anchored the whole Egyptian year. It is the once-a-year sky-marker the calendar was meant to open on (1 Akhet 1), and the herald of the inundation that fed the valley. Because Sirius is so bright and rises so close to the summer solstice, its dawn return gave priests a reliable yearly fixed point — the heartbeat against which the drifting civil calendar could be checked.

In Practice

When you read an Egyptian dated record, prt Spdt is the event that lets scholars pin it to an absolute year. Priests watched at predawn from a fixed spot for Sirius's first reappearance; a rising recorded in a known regnal year (famously Year 7 of Sesostris III, from the El-Lahun papyrus) becomes a candidate Julian date once you add the observation latitude and standard sky-visibility assumptions. The same dawn opened the New-Year festival and signalled the flood. Because Sirius has unusually high proper motion, its rising year recurred almost exactly every 365.25 days — so prt Spdt crept forward one day every four years against the 365-day civil calendar, the slow slippage behind the Sothic cycle. Parker once equated prt Spdt with the New-Year feast wpt rnpt, but Belmonte and Lull report that identification is now dismissed: the festival stayed fixed in the calendar while the actual star-rising drifted away from it.

Historical Origin

prt Spdt ("the going forth of Sothis") is attested as a standard Egyptian phrase from Old Kingdom feast-list discussions onward, with canonical use certain from the Middle Kingdom (Habicht et al. 2015). The earliest dated Sopdet-rising record is Year 7 of Sesostris III (Dynasty 12) on the El-Lahun temple papyrus. Treated in Clagett, *Ancient Egyptian Science* Vol II (1995), Ch. III, pp. 11-12 and Notes 15-16, and in Belmonte & Lull, *Astronomy of Ancient Egypt* (2018), §5.1, pp. 498, 504-505.

Definition

In Tradition

In Practice

Historical Origin

Further Reading