# Research in archaeoastronomy using computational, mathematical, and statistical methods, with free and open source software

[On this page I document and describe some of my work in archaeoastronomy, using mathematical, computational, and statistical methods to rigorously assess the probability that an archaeological site was used as an astronomical observatory.  I will give, as an example, all the programming code and other files I used to analyze a stone circle in the UK known as the "Merry Maidens".]

# Introduction to archaeoastronomy

Introduction

[This post is the first in a series on archaeoastronomy using open source software]

One of my academic hobbies is archaeoastronomy, which includes the study of how ancient peoples observed the sky.  As I will describe in a series of posts on this topic, I pursue my hobby with the use of free data and free software tools like Google Earth and the pyephem astronomical ephemeris calculation library, written in the Python programming language.

# Archaeoastronomy: a short overview of my methodology using open source software

[This post is part of a series of posts on archaeoastronomy using open source software]

My work focusses on using Google Earth, a downloadable free virtual globe and geographic information program, to obtain satellite imagery of aerially-visible archaeological sites world wide that are suspected to have been used for astronomical observations, for instance stone circles and medicine wheels.  The uniqueness of my approach is that it does not require actually having to visit these sites in person to survey them. Continue reading

# Archaeoastronomy: a description of the UK Merry Maidens site

[This post is part of a series of posts on archaeoastronomy using open source software]

The Merry Maidens are a late neolithic ring of stones near St.Buryan in Cornwall in the UK, and is Cornwall Archaeological Unit site SW433245. The site consists of a circular ring of 19 upright stones, approximately 24 m in diameter, and is believed to be remarkably intact.  The stones are not large, with the largest being approximately 1.4m (just over 4 feet) tall. The site is believed to date from somewhere between 2500BC to 1500BC.

Here is a photo of the site (source www.ancient-wisdom.uk):

# Archaeoastronomy: using Google Earth to obtain satellite imagery of archaeological sites

[This post is part of a series of posts on archaeoastronomy using open source software]

I use the free Google Earth software program to obtain satellite images of archaeological sites. If you download the Google Earth virtual globe program to your computer and start it up, in the search bar on the upper left hand side you can search for locations.

# Archaeoastronomy: using XFig to establish site datum points

[This post is part of of posts on archaeoastronomy using open source software]

Xfig is a free and open-source downloadable program for vector graphics widely used in physics.

In Xfig, I upload a satellite figure of an archaeological site, and then overlay circles over features in the site, trying to match as closely as possible their apparent diameter and position.

# Archaeoastronomy: using R to fit straight lines between archaeological site datum points

[This post is part of a series of posts on archaeoastronomy using open source software]

After you have obtained a satellite image of an archaeological site, uploaded the image to the XFig graphical software package, and placed datum points on site features, you can get XFig to output the datum point coordinate information into a text file in Computer Graphics Metafile (CGM) format.

You can then use the free and open-source R statistical programming language to read in the CGM files and fit straight lines between the datum points. R is not only a programming language, but also has graphics and a very large suite of statistical tools. Connecting models to data is a process that requires statistical tools, and R provides those tools, plus a lot more.

# Archaeoastronomy: where on the horizon do the stars, Sun, Moon rise and set? (Part I)

[This post is part of a series of posts on archaeoastronomy using open source software]

In astronomy, the observer’s coordinate system for observing a star (or the Sun or Moon) involves two coordinates, azimuth and altitude.

# Archaeoastronomy: calculating the horizon profile using free online sources of digitized topographic data

[This post is part of a series of posts on archaeoastronomy using open source software]

In order to calculate where stars rise and set on the horizon at a particular location, we need to know what the horizon looks like at that place… are there mountains along the horizon?  If so, they can substantially change the rise or set azimuth of a star, compared to a flat horizon.

The website HeyWhatsThat allows you to enter the latitude and longitude and elevation of any location on earth, and get the horizon profile. Here is what the screen shot of the input page looks like:

# Archaeoastronomy: where on the horizon do the stars, Sun, Moon rise and set? (Part II: correcting for the date the site was constructed)

[This post is part of a series of posts on archaeoastronomy using open source software]

In a previous post, we talked about the coordinate system of a person standing on earth observing a star (what the observer sees are the star altitude and azimuth), and how we can calculate the rise and set azimuths of stars/Sun/Moon at a given latitude if we know the equatorial declination coordinate of the star.  And we discussed that in the R file archeoastronomy_libs.R, there is a function called calculate_rise_set_azimuths() that will calculate the rise and set azimuths at a given latitude for a star with a given declination.

There are lots of places to look up catalogues of star declinations on the internet (for instance, here is one).  The SIMBAD astronomical database has a nice online query tool you can use to make your own custom list of stars. Continue reading

# Archaeoastronomy: the folly of too many lines

[This post is part of a series of posts on archaeoastronomy using open source software]

In these modules, we’ve been considering the problem of archaeological sites that we posit may have been observatories of the rise/sets of celestial bodies. “Site lines” are lines drawn between salient features of a site that we posit might have been used to sight along to look at a particular point on the horizon.

# Archaeoastronomy: was the Merry Maidens site an astronomical observatory?

[This post is part of a series of posts on archaeoastronomy using open source software.  And, to ensure that readers are not kept in undue suspense as they read through the analysis below, the answer is: Yes, it does appear that the Merry Maidens site was used to observe the winter sun solstice, and also was apparently used as part of a larger ceremonial complex along with nearby neolithic sites as a lunar observatory]

Step 1: fit the lines between the stones

If I fit straight lines between the centers of all pairs of stones, even if I only take lines with angular uncertainty of less than 1/10th of a degree, we end up with a total of 167  site lines:

# Archaeoastronomy: compendium of free sources of data and software

[This post is part of a series of posts on archaeoastronomy using open source software]

Satellite Imagery

I use the free Google Earth software program to obtain satellite images of archaeological sites. If you download the Google Earth virtual globe program to your computer and start it up, in the search bar on the upper left hand side you can search for locations.  In this module I describe how I use Google Earth to obtain satellite imagery of a site. Continue reading