PS 73-130
Ditching SI units to build an ecologically relevant measure of time and space

Thursday, August 13, 2015
Exhibit Hall, Baltimore Convention Center
Ty Tuff, Max Planck Institute for the Science of Human History, Jena, Germany
Barbara P. Buttenfield, Department of Geography, University of Colorado, Boulder, CO
Brett A. Melbourne, Department of Ecology and Evolutionary Biology, University of Colorado at Boulder, Boulder, CO

The sun powers life on Earth and life on Earth organizes itself accordingly. Understanding life’s organizational patterns requires a robust method for tracking the spatial and energetic relationship between Earth and the sun but there is a disconnect between measurements prescribed by the international system of standardizing units (SI) and the natural units of measurement used by organisms. For example, the current system of mapping data to Earth’s surface requires a complicated ‘clock time’ to track Earth’s spin. Anthropogenic measures, like ‘clock time’, lack ecological meaning and so tracking ecological trends from these measures becomes a game of comparing proxy variables representing the sun without capturing the full reality of the Earth/sun connection. I present a mathematical and conceptual framework for mapping the relationship between Earth and the sun using a set of 4 nested coordinate systems to account for relative motion between the two bodies. This integrated coordinate system maps the entire spatial relationship between Earth and the sun and standardizes that spatial relationship through time so that ecological patterns can be better visualized and understood.


It is known that a fixed point on Earth travels in a figure-8 pattern over the course of a year — a phenomenon arising from the combined 23° tilt and elliptical orbit of Earth. Consequently, an individual standing on the surface of Earth watches the sun move overhead in a figure-eight pattern throughout the year, while an individual floating above Earth watches Earth move below them in a mirror-image figure-8 pattern. This specific figure-8 pattern is called the Analemma and it defines the spatial relationship between Earth and the sun and acts as the null model for translating data between the Earth’s surface and areas of solar contact. The movement path of an individual will fall somewhere on a gradient between the Analemma seen from a surface perspective and the reverse Analemma seen from a detached solar perspective. I show that an individual will ultimately take a composite path created from a combination of two opposing Analemmas. Using examples from avian migration, I show that it is possible to deconstruct an individual’s composite path into its constituent attached vs. detached parts and, thus, identify the relative contributions of the sun and Earth in forming ecological spatial patterns.