As of March 2018, Photo Ephemeris Web shows the “ six-degree shadow circle ” as you adjust the timeline.
This short video explains:
What is the ‘Six-degree shadow circle’? from Crookneck Apps on Vimeo.
Shadow and Direction Indicators
When adjusting the time slider in the TPE web app, additional directional lines and a reference circle appear around the primary location pin. These indicators provide visual context for sun and moon position, direction, and shadow behavior at a given moment in time. These lines also display when you hold down the Shift key.
This article explains how to interpret these indicators and how they relate to light and shadow planning.
Set & Rise Direction Lines
The thick orange and blue lines extending from the pin indicate:
- Thick Orange Line: Sunrise and sunset directions
- Thick Blue Line: Moonrise and moonset directions
The thinner orange and blue lines represent the current azimuth (horizontal direction) of the sun or moon from the selected location. As the time slider is moved, these lines rotate to reflect the changing position of the sun and moon across the sky.
Current Location Direction Lines
When adjusting the time slider, you’ll see two additional lines and a circle. These thinner lines show the current position of the sun or moon if you were standing at the red pin and looking outward. As you move the time slider, these lines adjust accordingly, showing the sun and moon’s progression from east to west. Here’s what they represent:
- Thin Orange Line: This line shows the direction in which sunlight projects past the red pin, indicating where a shadow would be cast.
- Thin Blue Line: Similar to the orange line, this shows the direction of moonlight projection, useful for night photography or alignment purposes.
The thicker gray lines represent relative shadow lengths throughout the day. As sunset or moonset approaches, these lines lengthen, indicating longer shadows.
Terrain & Shadow Lines
For this demonstration, we’re using the Bonneville Salt Flats in Utah, one of the flattest places on Earth, to discuss shadows. The additional lines primarily relate to shadows cast on flat ground. It’s important to note that shadows cast on sloping terrain will differ in length due to simple geometry.
The 6-Degree Reference Circle
The circle centered on the pin is a visual reference tied to solar elevation. Its size is arbitrary and scaled to the map display.
When the sun’s shadow line reaches the radius of the circle, the sun is approximately six degrees above the horizon — and the circle turns orange. This elevation is commonly associated with the beginning of “ golden-hour ” lighting conditions, when shadows lengthen and contrast increases.
The circle functions as a reference guide rather than a physical distance measurement.
Moonlight and the Horizon
While the circle color doesn’t change for the moon, knowing when the moon is low in the sky can be useful. The horizon illusion makes the moon appear larger when near the horizon, especially when juxtaposed with known objects. Additionally, moonlight takes on a golden hue due to atmospheric scattering and refraction.
These shadow lines and the circle appear as you adjust the time slider. Once you release the slider, they disappear, returning to the default display. Holding the slider keeps them visible for further examination.
Next up: Using Photo Ephemeris Web, Part 7: 3D Celestial Sphere