Skip to content

IShadow and Sky

ESEN
Index
ESEN
Index

Chapter I · Act I — Reading Time

Shadow and Sky

c. 3500 BCE – 1st century

The first clock was a line of shadow; measuring time began with looking at the sky.

Before any machine, time was a shadow. Plant a stick in the ground and you watch its shadow swing round and shorten until noon, then lengthen towards the other side. The Egyptians raised obelisks and shadow clocks, and shared the daylight out into twelve parts.

The gnomon

Temporal hour I of XII · one hour = 60 min

Drag to turn it · arrow keys on a keyboard · double-click to face it

An obelisk at the latitude of Thebes (25.7° N), from sunrise to sunset. Geometric sun, no refraction.

  1. 1Gnomon
  2. 2Shadow
  3. 3Path of the tip
  4. 4Temporal hours

  1. At sunrise the obelisk’s shadow is endless and points west. As the sun climbs, it shortens and swings round.

  2. Its tip draws a different line on the ground every day: straight at the equinoxes, curved the rest of the year.

  3. The Egyptians divided daylight into twelve hours, summer and winter alike: temporal hours, of varying length.

  4. Change the season: in Thebes a summer hour lasts some 68 of our minutes, and a winter hour about 52.

Looking at the sky

  1. 3rd millennium BCE

    Counting in sixties

    Sumerians and Babylonians count in base sixty. Centuries later, astronomers will use it to divide the hour: hence its 60 minutes, and the 60 seconds of each minute.

  2. c. 2150 BCE

    Twelve and twelve

    On Egyptian coffin lids, star tables split the night into twelve: the rising of each star, a decan, opens a part. With shadow clocks, the day will have its twelve too, longer in summer than in winter.

  3. 1479–1425 BCE

    Egyptian shadow clocks

    A graduated bar and a crosspiece that casts its shadow along it, bearing the name of Thutmose III: the oldest sundial known. It divides the day into ten parts, and two of twilight.

  4. 1st century BCE

    Vitruvius and his dials

    In Book IX of De architectura, Vitruvius explains how to lay out a sundial with the analemma, and lists thirteen kinds, most of them with the name of their inventor.

The Line of Precision

The error a day of each chapter’s clocks, on a logarithmic scale. The line moves on with the story: each chapter draws its own stretch.

The line begins in the next chapter: a sundial never runs slow, because it defines the time it shows.

    This chapter’s sources