When breaking news footage, protest clashes, or military missile strikes appear on social media, bad actors frequently misrepresent archival footage as recent events or claim morning strikes occurred in the dead of night. While digital files can be stripped of EXIF timestamps, the physics of our solar system cannot be forged. If a photograph contains visible sun shadows cast by vertical structures, an investigator can pinpoint the exact time of day to within five minutes.

The premier open-source tool for calculating solar geometry is SunCalc (suncalc.org), alongside client-side astronomical calculators like Dawat’s Solar Chronolocator. This step-by-step tutorial teaches you how to calibrate true north, measure shadow azimuth rays, and solve for capture timestamps.

┌────────────────────────────────────────────────────────────────────────┐
│             ASTRONOMICAL CHRONOLOCATION VECTOR GEOMETRY                │
├────────────────────────────────────────────────────────────────────────┤
│                           SUN POSITION (Azimuth θ, Elevation α)        │
│                                    \                                   │
│                                     \                                  │
│                                      \  Ray of Sunlight                │
│                                       \                                │
│                                        ▼                               │
│                         [Vertical Pole / Wall (Height H)]              │
│                                        │                               │
│  Shadow Vector (Azimuth + 180°)        │                               │
│ ◄──────────────────────────────────────┴── Ground Plane                │
│             Shadow Length (L)                                          │
└────────────────────────────────────────────────────────────────────────┘

1. Deconstructing the SunCalc Interface

When you open suncalc.org, you are presented with a map overlay featuring colored rays radiating from a central pin:

┌────────────────────────────────────────────────────────────────────────┐
│                      SUNCALC VISUAL RAY LEGEND                         │
├────────────────────┬────────────────────┬──────────────────────────────┤
│ RAY COLOR          │ ASTRONOMICAL MEANING│ INVESTIGATIVE FUNCTION      │
├────────────────────┼────────────────────┼──────────────────────────────┤
│ Thick Orange Line  │ Current Sun Azimuth│ Points in direction of sun   │
│                    │                    │ at the selected time slider  │
├────────────────────┼────────────────────┼──────────────────────────────┤
│ Thin Black Line    │ Shadow Direction   │ Points in EXACT direction    │
│                    │ (Direct Opposite)  │ shadows will fall on ground  │
├────────────────────┼────────────────────┼──────────────────────────────┤
│ Yellow Curve       │ Daylight Sun Arc   │ Shows 24-hour solar path     │
│                    │                    │ across the sky on that date  │
├────────────────────┼────────────────────┼──────────────────────────────┤
│ Golden / Red Rays  │ Sunrise / Sunset   │ Pinpoints dawn/dusk azimuths │
└────────────────────┴────────────────────┴──────────────────────────────┘

[!IMPORTANT] The single most common mistake in amateur chronolocation is confusing the Sun Direction (Orange Line) with the Shadow Direction (Black Line). Shadows always point 180 degrees away from the sun:

$$\text{Azimuth}{\text{shadow}} = (\text{Azimuth} + 180^\circ) \bmod 360^\circ$$}

2. Step-by-Step Chronolocation Workflow

Step 1: Geolocate the Exact Ground Coordinates

Before you can determine the time, you must know the exact location. Identify the scene using satellite imagery (Google Earth, Bing Maps, or Sentinel Hub) and lock down the decimal latitude and longitude (e.g., 36.7538, 3.0588).

Step 2: Establish True North Calibration

Find a permanent vertical reference object in the photo that is also visible on satellite maps: - A light pole or flagpole. - The corner of a flat-roofed rectangular building. - A street curb running parallel to the scene.

Align the satellite view so that True North is oriented straight up ($0^\circ$).

Step 3: Measure the Shadow Vector Angle

Measure the angle of the cast shadow relative to True North using a digital protractor or QGIS line measurement tool: - If a flagpole shadow points toward the northeast at $45^\circ$, the sun must be shining from the southwest at $45^\circ + 180^\circ = 225^\circ$.

Step 4: Calculate the Object-to-Shadow Height Ratio

Measure the vertical height of the object ($H$) and the horizontal length of the cast shadow on flat ground ($L$). The solar elevation angle ($\alpha$) is calculated via basic trigonometry:

$$\tan(\alpha) = \frac{H}{L} \implies \alpha = \arctan\left(\frac{H}{L}\right)$$

• If a 10-meter utility pole casts a 10-meter shadow ($H/L = 1.0$), the solar elevation angle is $\arctan(1.0) = 45^\circ$.
• If the shadow is twice as long as the pole ($H/L = 0.5$), the elevation angle is $\arctan(0.5) \approx 26.6^\circ$.

3. The Critical “Time Zone Trap”

The primary pitfall in published investigative reports is time zone desynchronization:

1. SunCalc Defaults to Browser Local Time: By default, SunCalc calculates times in the local time zone of the investigator’s computer, not the location being analyzed. If an investigator in New York looks at an event in Kabul, Afghanistan, the default slider displays Eastern Time.
2. Daylight Saving Time (DST) Transitions: Check whether the target country observed Daylight Saving Time on the historical date of the event. Many nations (such as Turkey, Russia, and Iraq) abolished seasonal time changes entirely.
3. Always Report in Both Local and UTC: When filing an evidentiary report, state both the local solar time and Coordinated Universal Time (UTC) to eliminate cross-border ambiguity.

4. Evidentiary Verification Checklist

Before publishing conclusions based on shadow chronolocation: - Surface Slope Audit: Confirm that the ground where the shadow fell was flat. Shadows falling down a hillside or across stairs distort length measurements and produce false elevation angles. - Verticality Check: Ensure the shadow-casting pole is truly perpendicular ($90^\circ$) to the ground plane, not tilted by wind or collision damage. - Twin-Time Ambiguity (Morning vs. Afternoon): Because the sun passes through identical elevation angles twice each day (once climbing in the morning, once descending in the afternoon), you must use the shadow azimuth ray to eliminate morning/afternoon confusion.