1. Enter the mean Azimuth, geographic Latitude, and Horizon Altitude for the site.
  2. Specify the Tolerance, capturing the combined effect of all sources of uncertainty for date matching.
  3. Enter the foundation Year if known; otherwise, select the relevant Century.
  4. Use negative numbers for centuries and years BCE (e.g., -1 for 1st century BCE, -27 for 27 BCE); use positive numbers for CE centuries and years (e.g., 2 for 2nd century CE, 101 for 101 CE).
  5. Select Analyze Orientation to compute and view results.
  6. If matching dates are identified, results may be exported in CSV format via the Download Results option, including all corresponding Julian dates and JDN values.

For further details about each parameter, click the info icon (i) next to each field.

  • Dating range: The available date range begins in 27 BCE (start of the Roman Empire) and extends through 476 CE (end of the Western Empire). Calculations outside this period are not supported.
  • Solar range validation: The system notifies whether the computed declination is within or outside the solar range.
  • Date matching: When using “century” mode, results refer to the midpoint year of the selected century. For more precise results, use the exact foundation year if known.
  • Input validation: Entering values that are missing or not allowed (such as latitude below 19° or above 60°) will show an error message.
  • Calendar system: All output dates are in the Julian calendar.
Overview

ArchaeoSky is an interdisciplinary platform for the analysis of astronomical orientations of Roman archaeological sites. It is designed to support preliminary and exploratory research in archaeoastronomy, archaeology, and related fields by facilitating the systematic identification and assessment of alignments with solar phenomena, such as solstices, equinoxes, and other astronomically significant dates.

How it works

The current Manual Mode computes the solar declination for user-defined azimuth, latitude, and horizon altitude. Users additionally specify a tolerance, defining the acceptable angular deviation used for date matching.

When the orientation falls within the solar declination range, the platform identifies all Julian calendar dates within the selected chronology and the Roman Imperial period whose solar declination satisfies the specified tolerance. For each matching date, the associated Julian Day Number (JDN) is provided. Matching results can be exported in CSV format for further analysis.

If no astronomical alignment is identified, a relevant message is displayed.

Method

All solar positions in ArchaeoSky are computed using the Skyfield Python library (Rhodes 2019) together with the high-precision NASA JPL NAIF DE431 planetary and lunar ephemerides (Folkner et al. 2014). For user-defined azimuth, latitude, and horizon altitude, solar declinations are calculated following the methodology described in the literature (Ruggles 2015). JDN are computed internally by Skyfield, while Julian calendar dates are derived using the Meeus algorithm (Meeus 1998). All dates are referenced to the Julian calendar.

Development

ArchaeoSky is under active development, with future updates planned to support further analysis and advanced features.

  • Folkner, W. M., Williams, J. G., Boggs, D. H., Park, R. S., & Kuchynka, P. (2014). The planetary and lunar ephemerides DE430 and DE431. IPN Progress Report, 42-196, Jet Propulsion Laboratory, California Institute of Technology.
  • Magli, G., González-García, A. C., Belmonte, J. A., & Antonello, E. (Eds.). (2019). Archaeoastronomy in the Roman World. Springer.
  • Meeus, J. (1998). Astronomical Algorithms (2nd ed.). Willmann-Bell Inc.
  • Rhodes, B. (2019). Skyfield: High precision research-grade positions for planets and Earth satellites generator. Astrophysics Source Code Library, record ascl:1907.024.
  • Rodríguez-Antón, A., González-García, A. C., & Belmonte, J. A. (2018). An Archaeoastronomical Approach to Roman Urbanism: Orientation of Roman Settlements Across the Empire. Mediterranean Archaeology and Archaeometry, 18(4), 89–95.
  • Ruggles, C. L. N. (Ed.). (2015). Handbook of Archaeoastronomy and Ethnoastronomy. Springer.