OneTaskBy Tim King · Updated
Sun Path Simulator
Sun Position by Location and Date, Free
OneTask is free, with no sign-up, and built by one person.
If this tool saved you time, a coffee helps keep new ones coming.
How the Sun Path And Shadow Simulator works
This sun path simulator draws the sun's arc for any place. Enter a latitude, longitude, date and time and this page draws the sun's arc across the sky for that day, the sun's position at the chosen hour and the shadow a vertical pole throws on the ground, all in a 3D scene you can orbit. Fainter arcs show the summer solstice, winter solstice and equinox for comparison, and the rail lists sunrise, sunset, day length, solar noon, the sun's elevation and azimuth and the shadow's length.
Sun path simulator: what the scene shows
The disc is the ground with north, east, south and west marked around the edge. The yellow arc is the sun's path for the chosen date, from where it rises on the eastern side to where it sets on the western, and the yellow ball is its position at the chosen local time. The pole in the centre casts a dark shadow directly away from the sun, and the thin line from the pole's tip to the sun shows the ray that defines the shadow's end. Drag the time slider through the day to watch the shadow swing from west to east and shorten toward noon. The grey arcs, which can be switched off, show the same path on the June solstice, the December solstice and the March equinox, so you can see how high the sun climbs across the year at your latitude.
Location, date and time zone
Latitude is positive north of the equator and longitude positive east of Greenwich, so London is 51.5, −0.13 and Sydney is −33.87, 151.21. The time slider is local clock time; the UTC offset box tells the page what that clock means, and it is filled in from your browser's time zone when the page loads. Set it by hand when you are looking at a place elsewhere in the world: Sydney is +10, or +11 in southern summer; New York is −5, or −4 in daylight saving. An offset that does not match the location shifts every reported time by the same amount but does not change the shape of the arc.
How the position is worked out
The sun's declination and the equation of time come from the standard low-precision solar formulas used in astronomical almanacs, good to a fraction of a degree, and the hour angle follows from the longitude and the time. Elevation and azimuth are then ordinary spherical trigonometry. Sunrise and sunset are the moments the centre of the sun crosses 0.833 degrees below the horizon, which allows for refraction and for the sun's radius, matching the times printed in newspapers. No correction is made for altitude or for hills on the horizon.
Shadow length
A pole of height h under a sun at elevation e throws a shadow of h divided by tan(e). At 45 degrees the shadow equals the height; at 10 degrees it is nearly six times as long; and the rail reports both the length in metres and the ratio, so the figure can be scaled to any object. Change the pole height to match a building, a tree or a fence post to check what it will shade at a given hour, or to test where a solar panel or a garden bed will be in sun.
FAQ
Why does the shadow point north at noon?
In the northern hemisphere the sun is due south at solar noon, so shadows fall to the north; south of the equator it is the reverse. Between the tropics the noon sun can be on either side depending on the date, and on two days a year it is exactly overhead and the pole has no shadow at all.
What happens in the Arctic or Antarctic?
When the sun never sets the rail says so and the day length is 24 hours; when it never rises there is no path to draw and the shadow is absent. The threshold is the same 0.833 degrees used for ordinary sunrise, so a day with a sliver of sun at midnight still counts as sun up.
Does solar noon happen at 12:00?
Rarely. Solar noon drifts with your position inside the time zone and with the equation of time, which adds or subtracts up to sixteen minutes over the year. Daylight saving pushes it another hour later on the clock. The rail gives the true solar noon and the sun's height at that moment.
How accurate are the sunrise and sunset times?
Typically within a minute or two of published tables. The formulas ignore your altitude above sea level and any mountains on the horizon, both of which change the real moment the sun appears, and refraction varies slightly with the weather.
See also: all 3D Science tools, Images, Audio, Video & Screen, PDF, SVG, Simulations & Screensavers, Generative Art, Chart Makers, 3D Model Viewers, Drawing Pads, Mockups & 3D Making, Diagram Makers, Tracker Music.
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