Elevation
—
degrees above the horizon — 0° is sunrise or sunset, 90° is directly overhead
Loading the selected sky.
- Visible light—
- UVA—
- UVB—
Where the sun is
The sun's angle above the horizon at this moment, and what that angle puts in the light reaching you.
Sun through the day
How the angle moves from sunrise to sunset, and which hours actually carry vitamin D and sunburn.
The black line is the sun's height through the day; the two bars beneath it show what that height delivers. The sunburn bar starts earlier and finishes later than the vitamin D bar — the shaded columns are those hours, when you can still burn and synthesis has already stopped.
The background colour is the sun's own colour at that height.
Why the sun's arc tilts
The sun's daily path across the sky dome at the two solstices, and the cone it has to enter before vitamin D synthesis has light to work with.
The two solid arcs are the sun's path on the June and December solstices; the dashed one is the date you have selected. The cone sits at 45°, and the circle on the ground has the figure's own height for its radius: the sun is inside the cone exactly when your shadow is shorter than you are. Slide the latitude below — past roughly 20°N the December arc stops entering that cone for months on end, and past roughly 67°N it stops clearing the horizon entirely.
This scene needs WebGL, which this browser has not made available. The hours below are the same numbers the picture would have drawn, from the same astronomy.
- 45° cone — shadow at your height
Hours above 45°
Every day of the year
The same reading repeated for all 365 days, at any latitude — where the vitamin D window opens, and where it closes.
Each cell is coloured by how high the sun is at that moment, and the dashed line rings the region where enough UVB reaches the ground for vitamin D synthesis to run. Drag the latitude slider upward and watch that region close: past roughly 37° a hole opens through the middle of the year — months during which the sun never climbs high enough, on any day, at any hour.
Your day in words
A plain-text summary of the selected day, written for the skin type you pick below.