#archaeoastronomy

By Girtompir - Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=57252822

The stars have long been part of the human experience, with the night sky being a more vital part of life before the development of modern cities with their lights washing out a majority of the stars. Most cultures had a deep connection with the sky, recording their observations in stories and in their art and writings.

CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=906430

Archaeoastronomy is an interdisicplinary study of how people 'have understood the phenomena in the sky, how they used these phenomena and what role the sky played in their cultures'. It involves ethnoastronomy, the 'anthropological study of sky watching in contemporary societies' as well as historical astronomy, which focuses on the astronomical records of the past. Unlike modern astronomy, which focuses on observations of the sky and scientific explanations of those observations, archaeoastronomy takes in account the cultural meanings of those observations.

By Alun Salt - https://www.flickr.com/photos/alun/2733498/in/set-68848/, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=740899

Archaeoastronomy began with noting the astronomical orientation of ruins, including megalithic sites like Stonehenge, in the 17th and 18th centuries, though the term wasn't coined until 1973 by Elizabeth Chesley Baity. It wasn't until the 1960s that systemic work began by studying megalithic sites in the British Isles. Engineer Alexander Thom and astronomer Gerald Hawkins proposed that Stonehenge was an astronomical computer. While Hawkins' theory was dismissed, Thom performed a survey of megalithic sites in the British Isles. Euan MacKie sought to test Thom's theory by excavating the site of a standing stone at Kintraw in Argyllshire from 1970-1971 to verify if Thom's prediction that the site accurately showed the winter solstice. He found an observation platform on the hill above the stone that proved Thom's prediction correct. Because of this vindication, MacKie checked other sites to verify their alignments before broadly accepting Thom's conclusions.

By Adrian Hernandez - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=71192285

Archaeoastronomy was used by anthropologists studying Amerindian civilization. This was different to the study of Neolithic structures in the British Isles in that there were sources about the prehistory, such as the records of colonizers, that were unavailable for British early civilizations. This allows more certain claims that possible in the Old World.

Public Domain, https://commons.wikimedia.org/w/index.php?curid=1126668

In 1981, the International Astronomical Union (IAU) released two volumes on the proceedings from the conference that sought to bring researchers together and encourage the move to interdisciplinary approaches, combining the contextuality of archaeological studies with astronomical studies, seeking to understand the why behind ancient people's fascination with the night sky.

By Fcb981 - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=3862230

The Nebra Sky Disc - bronze, gold - Unetice culture - Early Bronze Age - c.1800-1600 BCE

The Nebra sky disc is a bronze disc of around 30 cm (12") diameter and a weight of 2.2 kg (4.9 lb), having a blue-green patina and inlaid with gold symbols. These symbols are interpreted generally as the Sun, a lunar crescent, and stars (including a cluster of seven stars interpreted as the Pleiades). Two golden arcs along the sides, interpreted to mark the angle between the solstices, were added later. A final addition was another arc at the bottom with internal parallel lines, which is usually interpreted as a solar boat with numerous oars, though some authors have also suggested that it may represent a rainbow, the Aurora Borealis, or a comet.

The disc was found buried on the Mittelberg hill near Nebra in Germany. It is dated by archaeologists to c. 1800–1600 BCE and attributed to the Early Bronze Age Unetice culture. It served as a reminder of when it was necessary to synchronize the lunar and solar years by inserting a leap month. This phenomenon occurred when the three-and-a-half-day-old moon —the crescent moon on the disc— was visible at the same time as the Pleiades. As preserved, the disc was developed in four stages:

Initially the disc had thirty-two small round gold circles, a large circular plate, and a large crescent-shaped plate attached. The circular plate is interpreted as the Sun, the crescent shape as the Moon, and the dots as stars, with the cluster of seven dots likely representing the Pleiades star cluster.  At some later date, two arcs (constructed from gold of a different origin, as shown by its chemical impurities) were added at opposite edges of the disc. To make space for these arcs, one small circle was moved from the left side toward the center of the disc and two of the circles on the right were covered over, so that thirty remain visible. The two arcs span an angle of 82°, correctly indicating the angle between the positions of sunset at summer and winter solstice at the latitude of the Mittelberg (51°N).  The final addition was another arc at the bottom, identified as a solar boat, again made of gold, but originating from another different source. By the time the disc was buried it also had 38 to 40 holes punched out around its perimeter, each approximately 3 millimetres (0.12 in) in diameter. 

Halley's Comet in the 11th century Bayeux Tapestry l via NASA

Near as I can tell, the halfway point between the Spring Equinox and the Summer Solstice (called the Celtic cross quarter of Beltane, though it predates the Celts and goes back to early agrarian cultures) is today, May 5, 2023, at 7:35 PM Pacific Daylight Time.