How we calculate eclipse times

Every time and duration on this site is calculated from the positions of the Sun and Moon for a specific point, rather than copied from other websites.

The model

We use Astronomy Engine, an open-source library based on the same planetary and lunar theories used by professional ephemerides. For each place we search for the local circumstances of the 2 August 2027 eclipse: the four contact times, the moment of maximum eclipse, the fraction of the Sun covered, and the height and direction of the Sun.

Coordinates

Each town page uses a single point near the town centre, shown on the page. Because the path edges are sharp, a few kilometres can change the duration noticeably near the northern or southern limit of the path. For your exact viewing spot, use the calculator on the home page.

Accuracy and limits

The calculation treats the edge of the Moon as a smooth circle. In reality, lunar mountains and valleys let the last beads of sunlight through a little earlier or later, so published figures that model the lunar profile can differ from ours by a few seconds. Near the edges of the path the difference can be larger, which is another reason to aim for a spot well inside it.

Weather figures

Clear-sky percentages come from the long-term satellite cloud climatology published by eclipse meteorologist Jay Anderson. They describe the historical odds for early August, not a forecast.

Corrections

If you find a figure that looks wrong, please write to us through the About page. We check every report against the model and published sources.