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Astronomy

Sun Position & Shadow Length Simulator

· Last updated：2026-06-22

Compute the sun’s elevation and azimuth (NOAA algorithm) for any latitude, longitude, date and time, plus the length and direction of the shadow cast by an object of a given height, with sunrise/sunset and a full-day shadow curve

Details

What this tool helps you do

Enter latitude, longitude, a date/time and the height of an object (a pole, a building, a tree), and the tool computes:

  • Sun elevation (altitude above the horizon) and azimuth (compass bearing, 0=N, 90=E) using the NOAA/Spencer solar position algorithm.
  • Shadow length on the ground = object height ÷ tan(elevation), shown both in absolute units and as a multiple of the object height.
  • Shadow direction (the antipode of the sun azimuth — where the shadow tip falls from the object's base).
  • Sunrise / solar noon / sunset in local standard time, including polar-night / midnight-sun detection.
  • A full-day curve of elevation and shadow length, with the selected moment marked, and a top-down shadow plan showing the object, sun ray, and cast shadow.

Algorithm details:

  • Solar declination via Spencer's series; equation of time via the NOAA 3-term approximation.
  • Apparent elevation includes NOAA's piecewise atmospheric-refraction correction (accurate near the horizon).
  • You can choose UTC (input time treated as UTC), or local solar time (time-of-day at the longitude, ignoring time-zone and DST — handy for a "where is the sun at 10am solar time" answer).

Accuracy is ~±0.5° in elevation/azimuth for years 1950–2050 — ideal for solar panel siting, architectural shadow studies, gardening, photography planning, or film/game level design.

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Written by the Elysia Tools team
Length59

Tool usage guide

Learn when to use this tool, what it supports, and how real users apply it.

Key facts

Category
Astronomy
Input types
number, date, select
Output type
html
Sample coverage
4
API ready
Yes

Overview

The Sun Position & Shadow Length Simulator computes the sun's precise elevation and azimuth using the NOAA solar position algorithm for any latitude, longitude, date, and time. It also simulates the exact length and direction of a shadow cast by an object of a specified height, providing sunrise, sunset, solar noon times, and a full-day shadow curve.

When to use

  • Planning solar panel installations to determine optimal tilt angles and avoid shading from nearby structures.
  • Designing architectural layouts or landscaping projects that require detailed seasonal shadow analysis.
  • Scheduling outdoor photography or film shoots to capture specific lighting angles and shadow lengths.

How it works

  1. 1Input the geographic coordinates (latitude and longitude), date, time, and the height of the object casting the shadow.
  2. 2Select the time basis, choosing either UTC with a timezone offset or local solar time to ignore daylight saving adjustments.
  3. 3The simulator applies the NOAA/Spencer solar position algorithm, incorporating atmospheric refraction corrections, to calculate the sun's elevation and azimuth.
  4. 4It outputs the shadow length and direction, alongside sunrise, solar noon, sunset times, and a visual full-day shadow curve.

Use cases

  • Determining the height limits of new fences or buildings to prevent blocking sunlight to neighboring gardens.
  • Calculating the exact time of day when a specific landmark will cast a shadow over a target area.
  • Optimizing agricultural crop placement based on daily and seasonal shade patterns from surrounding trees.

Examples

1. Summer Solstice Shadow Analysis in New York

Landscape Architect

Background

A landscape architect needs to know the minimum shadow cast by a 1.8-meter decorative pillar in a New York park during the summer solstice.

Problem

Determine the shortest shadow length and its direction at solar noon to ensure it does not block a nearby walkway.

How to use

Set latitude to 40.7128, longitude to -74.006, date to 2026-06-21, hour to 12, object height to 1.8, and time zone basis to local solar time.

Latitude: 40.7128, Longitude: -74.006, Date: 2026-06-21, Hour: 12, Height: 1.8, Time Basis: solar

Outcome

The simulator calculates a sun elevation of approximately 72.6° and a shadow length of 0.57 meters pointing directly north.

2. Winter Shadow Projection for a London Building

Urban Planner

Background

An urban planner is evaluating the shadow impact of a proposed 10-meter building in London during the winter solstice.

Problem

Calculate the maximum shadow length at 3:00 PM (15:00) UTC to assess light blockage on adjacent properties.

How to use

FAQ

How accurate is the solar position calculation?

The simulator uses the NOAA/Spencer algorithm, which provides an accuracy of approximately ±0.5° for the years 1950 to 2050.

What is the difference between UTC and local solar time?

UTC uses standard clock time adjusted by your timezone offset, while local solar time calculates the sun's position based strictly on your longitude, ignoring time zones and daylight saving time.

How is the shadow direction determined?

The shadow direction is calculated as the antipode (opposite angle) of the sun's azimuth, indicating where the shadow tip falls relative to the object's base.

Does the simulator account for atmospheric refraction?

Yes, it includes NOAA's piecewise atmospheric-refraction correction, which ensures high accuracy even when the sun is near the horizon.

Can this tool detect polar nights or midnight sun?

Yes, the algorithm automatically detects and displays polar night and midnight sun conditions based on the input latitude and date.

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Input latitude 51.5074, longitude -0.1278, date 2026-12-21, hour 15, object height 10, timezone offset 0, and time basis UTC.

Latitude: 51.5074, Longitude: -0.1278, Date: 2026-12-21, Hour: 15, Height: 10, TZ: 0, Time Basis: utc

Outcome

The tool determines the low sun elevation angle, showing a long shadow extending far to the northeast, along with the full-day shadow curve.