Science & history · The Sun and Earth's sky
The Sun's geometry cannot forecast clouds
This site can tell you, to the second, when the Sun will be 18° below your horizon. It cannot tell you whether you will see a single star.
What the calculation knows
The times on these pages follow from the Sun's position and USNO's definitions. Even those come with a warning: real rise and set times depend on unpredictable atmospheric conditions.
What it does not
Clouds, haze, smoke, moonlight and streetlights are separate questions. At Newgrange, where the solstice sunrise has been watched for decades, the staff say it is impossible to forecast what one patch of sky will do at sunrise. Where this site shows a forecast, it says whose it is, for when, and what it covers.
Sources
- US Naval Observatory Rise, Set, and Twilight Definitions (opens in a new tab) for sunrise/sunset and the three twilights; refraction and accuracy caveats · checked 2 October 2026
- Office of Public Works (Clare Tuffy) Behind the Scenes at Newgrange at the Winter Solstice (opens in a new tab) for the lottery since 2000; no forecast can say what a patch of sky will do at 8.58 a.m. · checked 2 October 2026