Babylonian Astronomical Diaries: 600 Years of Sky Records

The Babylonian Astronomical Diaries are a series of cuneiform clay tablets on which scribes at Babylon recorded what they saw in the sky night after night, together with the weather, the level of the Euphrates, market prices and news of the day. Dated diaries run from 652 BC to 61 BC, making them the longest continuous programme of scientific observation known from the ancient world. They are a key source both for the history of astronomy and for the history of Babylon under Assyrian, Babylonian, Persian, Macedonian and Parthian rulers.

What the diaries contain

A typical diary covers half a year, divided into months and then into individual nights. For each night the scribe noted the position of the Moon relative to nearby reference stars, measured in units called cubits and fingers. Planetary positions, the first and last visibility of planets, eclipses and solstices were also recorded.

Each month usually closes with a fixed set of entries. These give the prices of six commodities in Babylon (barley, dates, cuscuta, once translated as mustard, cress, sesame and wool), the position of the planets, the changing level of the river and a short section on events. The price data make the diaries one of the best sources for the economic history of any ancient society.

Weather is recorded in detail: clouds, rain, thunder, fog, strong winds and dust storms. When bad weather prevented observation, the scribes often wrote “not observed” or entered a calculated value instead.

How a diary was made

The scribes probably first wrote short notes during or soon after each night of observation. These were later copied into monthly sections and finally into neat tablets covering six or seven months. Some tablets carry a heading that describes the text as part of the “regular watching” of the sky.

Observations were made with the naked eye, without telescopes or elaborate instruments. Time intervals, such as the gap between sunset and moonset, were given in units called UŠ, equal to about four minutes.

Dating and survival

The oldest dated diary covers part of 652 BC, in the reign of Shamash-shum-ukin, the Assyrian-backed king of Babylon. Another early and famous example, a tablet now in Berlin known as VAT 4956, covers 568–567 BC, the 37th year of Nebuchadnezzar II. Because its observations can be matched to modern calculations of the sky, it is important for fixing the chronology of the Neo-Babylonian period.

Most surviving tablets date from the 4th to the 1st centuries BC. The last dated diary is from 61 BC. Hundreds of tablets and fragments survive, but they cover only part of the six centuries, so the original series was far larger than what remains.

Most diaries reached the British Museum in the late 19th century, after local diggers uncovered them at Babylon. Their exact findspot is unknown, though many scholars think they came from an archive connected with the Esagila, the temple of Marduk. Their systematic publication began with the work of Abraham Sachs, continued after his death by Hermann Hunger, in a series printed in Vienna from 1988.

History in the margins

The diaries’ event sections give rare, contemporary Babylonian views of famous episodes. The diary for 331 BC records an eclipse of the Moon before the Battle of Gaugamela and refers to the defeat of the Persian king’s army and the entry of Alexander’s army into Babylon. Another diary notes, under a date in June 323 BC, that “the king died”, the earliest record of the death of Alexander the Great.

Other entries mention epidemics, famines, temple affairs, fires and the movements of Seleucid and Parthian kings. Because they were not written as royal propaganda, they are often more neutral than official inscriptions.

Purpose and legacy

Most historians link the diaries to the long tradition of Mesopotamian sky divination, in which events in the heavens were read as signs from the gods. Scribes in the service of the temple were paid to keep a “regular watch” of the sky, and the habit of recording weather and prices alongside the stars suggests they looked for patterns linking the heavens to life on earth.

Over time the records were reused to compile other kinds of texts. Goal-Year Texts collected observations from earlier cycles to predict events, and almanacs listed expected phenomena for the coming year. This accumulated data helped Babylonian astronomers develop the mathematical methods of the late first millennium BC, which in turn influenced Greek astronomers such as Hipparchus. The diaries thus continue a scientific tradition that includes earlier texts such as the Venus Tablet of Ammisaduqa.

Timeline

• 652 BC: Earliest dated surviving diary is written in Babylon.
• 568–567 BC: Diary VAT 4956 records observations from Nebuchadnezzar II’s 37th year.
• 331 BC: Diary records the lunar eclipse before Gaugamela and Alexander’s arrival.
• 323 BC, June: A diary notes the death of Alexander the Great at Babylon.
• 61 BC: Latest dated diary.
• 1870s–1880s: Tablets from Babylon are acquired by the British Museum.
• 1988: First volume of the Sachs–Hunger edition is published in Vienna.

Why it matters

The Astronomical Diaries are an unbroken window, though full of gaps, onto six centuries of observation, weather, prices and politics at Babylon. They show that systematic, long-term data collection, a foundation of modern science, was already practised in the ancient Near East.