How to Use SunCalc.org to Check Sun Position, Sunrise/Sunset, and Shadow Length

SunCalc.org is a free browser-based sun calculator that shows, for any place and date, the sun's path across the sky along with sunrise, sunset, culmination, altitude, azimuth, and shadow length. You set a location on an interactive map or by entering coordinates, pick a date, and drag a time slider to watch the sun move. It works for planning photography, checking whether a spot gets shade at a given hour, sizing a solar panel setup, or just understanding how the sun behaves at your latitude across the year.

Setting Your Location

The calculator needs a place before it can compute anything. You have two ways to give it one:

• Click the map. The interactive map centers on your chosen point, and the coordinates update automatically.
• Enter coordinates directly. Use the Lat and Lon fields to type a latitude and longitude, then apply them with the Set Lat/Lon control.

After the location is set, confirm the time zone (TZ) and the DST setting. These matter because sunrise and sunset are reported in local clock time — if the time zone or daylight-saving flag is wrong, every time in the output shifts. The panel also shows the location's height (elevation) and a UTM coordinate, which are useful if you're matching the tool against survey or mapping data.

Picking a Date and Moving Through the Day

Use the month selector (Jan through Dec) and the date range controls to choose the day you care about. Then move through the day with the time slider:

• Drag the sun on the slider with the mouse, or
• Use the arrow keys on your keyboard for finer steps.

The colors on the time slider represent the sunlight phase during the day, so you can see at a glance when it's dark, when the sun is low, and when it's high. There's also a LIVE mode that tracks the sun in real time; click STOP-LIVE to end it and return to manual control.

Reading the Output

Once a location and time are set, the panel reports the day's key solar events and the sun's current position:

The shadow length figure is tied to an object height you specify (the "at an object level [m]" input). Set the height of the object — a person, a building, a pole — and the tool returns how long its shadow will be at the selected time. This is the number to check when you want to know whether a wall, tree, or neighboring building will shade a spot at 3 p.m. in June.

Understanding the Sun-Path Curve

The map draws the sun's trajectory as a thin yellow curve. Two things to read from it:

• The curve itself is the sun's path for the selected day.
• The yellow band around it shows how that path shifts across the whole year — the spread between the shortest and longest days.

The closer a point on the curve is to the center of the display, the higher the sun is above the horizon. So a curve that bulges far toward the center means a high summer sun; a flatter curve hugging the edge means a low winter sun. Comparing the band's edges tells you how much the sun's path changes between seasons at your latitude.

Reverse Calculation and Photovoltaic Data

Two extra features handle more specific tasks:

• Reverse Calculation works backward from a shadow to the object or angle that produced it — useful when you've measured a shadow and want to infer the sun position or object height.
• Photovoltaic section reports solar constant, air mass, and irradiance for the selected location and time. These are the inputs you'd want when estimating how much sunlight a panel would receive, rather than just where the sun is.

The panel also lists astronomical values such as declination, right ascension, GMST, GHA, JDE, and DeltaT, plus the dates of the equinoxes and solstices. These are reference figures for anyone doing more precise solar or astronomical work.

Printing and Saving Results

The tool offers three print options: Print – Current Data, Print – Data this day, and Print – Current Map. Use these to keep a record of a specific moment, a full day's solar table, or the map view with the sun path drawn on it.

Practical Notes

• If times look off by an hour, recheck the DST setting first — it's the most common source of confusion.
• The shadow length depends entirely on the object height you enter, so set that before reading the number.
• The site also links to companion tools for the moon (mooncalc.org), planets (planetscalc.org), and satellites (orbtrack.org) if you need the same kind of position data for other objects.
• A German-language version is available at sonnenverlauf.de.