Alpha Piscium renders its sky using the Unreal Engine Sky Atmosphere technique — a physically-based model that simulates Rayleigh scattering, Mie scattering, and ozone absorption through separate, individually tunable coefficients. Volumetric light shafts (god rays) are computed with epipolar sampling, which projects the atmosphere along radial lines emanating from the sun, dramatically reducing the cost of high-quality light shaft rendering compared to naive ray marching. Together these systems produce a sky that responds correctly to every time of day, from the crisp blue noon to the deep orange haze of sunrise and the ink-blue clarity of midnight.Documentation Index
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Scale
Atmosphere Scale
Atmosphere Scale
Altitude scale factor. A value of 1 means 1 block = 1 km; a value of 1000 means 1000 blocks = 1 km. Raise this value if the atmosphere looks too thin or if fog fades out too rapidly at low altitudes.
Distance scale factor. A value of 1 means 1 block = 1 km; a value of 1000 means 1000 blocks = 1 km. Adjusting this independently from the altitude scale allows the horizon haze to change without affecting the sky gradient height.
Ground Albedo
Ground Color
Ground Color
The ground albedo is the color of light that bounces off the terrain back into the atmosphere. It tints the horizon and affects the overall sky color, particularly at low sun angles.
Red component of the ground albedo color (0–255). Affects warm horizon tones at sunrise and sunset.
Green component of the ground albedo color (0–255). Affects the mid-tone of light reflected from the terrain.
Blue component of the ground albedo color (0–255). Affects the cool blue tint at twilight.
Light Shafts (Epipolar Sampling)
Epipolar Light Shaft Quality
Epipolar Light Shaft Quality
These settings control the quality of the epipolar-sampled volumetric light shaft pass. Higher values improve quality but increase GPU cost proportionally.
Number of epipolar slices used for volumetric lighting. Valid values: 256, 512, 1024, 2048. Higher values produce more detailed light shaft boundaries at greater performance cost.
Number of samples per epipolar slice. Valid values: 128, 256, 512, 1024. Controls how finely each slice is sampled along the ray toward the sun.
Samples for the volumetric light shaft ray march (god rays). Valid values: 4–32. Higher values create smoother, more detailed rays.
Shadow samples evaluated within light shaft rays. Valid values: 1–16. Higher values improve shadow accuracy inside god rays.
Shadow samples used specifically for depth break correction in light shafts. Valid values: 8–64. Prevents halos where light shafts intersect geometry at depth discontinuities.
How soft and diffused the light shaft edges appear. Valid values: 0–10. Higher values create wider, more atmospheric rays; lower values produce sharper beams.
Enables depth break correction for light shafts. When enabled, prevents light shaft halos that appear where foreground geometry meets the sky at depth boundaries.
Sky Rendering
Sky View Resolution and Samples
Sky View Resolution and Samples
Resolution of the sky view LUT (look-up texture). Valid values: 128, 256, 512, 1024. Higher values improve sky color gradient accuracy, especially near the horizon, at the cost of GPU memory and compute.
Number of integration samples for sky transmittance calculations. Valid values: 16, 24, 32, 40, 48, 56, 64. Higher values improve accuracy for the sky color during complex lighting conditions.
Mie Scattering (Haze & Fog)
Global Turbidity
Global Turbidity
Mie scattering is responsible for the whitish haze that fills the atmosphere near the horizon and around the sun. Higher turbidity values create a denser, mistier atmosphere reminiscent of humid or polluted air. The actual turbidity value applied is 2^x, where x is the setting value.
Base Mie turbidity (overall atmospheric haziness). Range: 0.0–8.0. The actual coefficient is 2^x. A value of 0 gives a near-pristine clear sky; higher values produce heavier haze.
When enabled, turbidity is automatically modulated by time of day, applying the per-time values below. Disable to use only the global turbidity value across all hours.
Per-Time-of-Day Turbidity
Per-Time-of-Day Turbidity
When
SETTING_ATM_MIE_TIME is enabled, these values override the global turbidity at each time of day. All values use the 2^x scale and range from 0.0 to 8.0. Default values reflect a natural diurnal haze cycle with peak haziness at sunrise and midnight.Atmospheric haze during early morning hours, before sunrise. Actual value: 2^x.
Atmospheric haze at sunrise — the peak turbidity time by default, creating vivid warm colors.
Atmospheric haze during morning hours after sunrise, as the sky clears.
Atmospheric haze at noon — the default clearest point of the day.
Atmospheric haze during afternoon hours. Set lower than noon by default for crisp afternoon light.
Atmospheric haze at sunset, producing warm orange and red color tones.
Atmospheric haze during early night hours.
Atmospheric haze at midnight. Higher default value creates a slightly murky night sky.
Mie Coefficients
Mie Coefficients
These multipliers scale the underlying Mie scattering and absorption coefficients independently of turbidity, allowing fine control over how haze looks without changing its density.
Mie scattering multiplier. Range: 0.0–5.0. Controls how brightly haze scatters light. Higher values produce a brighter, more luminous haze around the sun and near the horizon.
Mie absorption multiplier. Range: 0.0–2.0. Controls how much light is absorbed by haze particles. Higher values darken the haze, creating murkier, heavier atmospheric fog.
Rayleigh Scattering and Ozone
Rayleigh and Ozone Coefficients
Rayleigh and Ozone Coefficients
Rayleigh scattering multiplier. Range: 0.0–5.0. Controls the intensity of the blue sky color produced by molecular scattering. Higher values deepen and saturate the blue sky; lower values produce a paler or more white sky.
Ozone absorption multiplier. Range: 0.0–5.0. Simulates the ozone layer’s effect of absorbing yellow-green wavelengths, which enhances the blue and purple hues visible in the sky dome during sunrise and sunset.
Sun
Sun Appearance
Sun Appearance
Size of the sun disc. A value of 1.0 represents the realistic solar radius. Valid values span from 0.0078125 to 1024.0 (scale multiplier). Larger sun discs produce softer, wider shadow penumbras via PCSS.
Distance of the sun in astronomical units (AU) relative to the real sun distance of 149.6 million km. Valid values span from 0.0078125 to 1024.0. Changing distance while keeping radius constant alters the apparent angular size of the sun.
Angle of the sun’s arc across the sky in degrees. Range: −90.0 to 90.0. Negative values tilt the sun’s path toward the northern horizon (as seen from northern hemisphere perspective); positive values tilt it toward the south. Default −20° provides a natural non-overhead sun path.
When enabled, uses the actual solar color temperature of 5772 K for an accurate warm yellow-white sunlight color. When disabled, the value from
SETTING_SUN_TEMPERATURE is used instead.Color temperature of sunlight in Kelvin. Range: 1000–50000 K. Only active when
SETTING_REAL_SUN_TEMPERATURE is disabled. Lower values (2000–3000 K) produce warm amber sunset light; higher values (8000+ K) produce cool blue-white light.Moon
Moon Appearance
Moon Appearance
Size of the moon disc. A value of 1.0 represents the realistic lunar radius. Valid range: 0.0078125–1024.0 (scale multiplier).
Distance to the moon relative to its real-world distance of 384,399 km. Valid range: 0.0078125–1024.0. Affects the moon’s apparent size in the sky.
Reflectivity of the moon surface. Range: 0.01–1.0. The default of 0.12 is physically accurate — the real Moon reflects approximately 12% of incoming sunlight. Higher values create brighter nights.
Moon Tint Color
Moon Tint Color
The moon tint multiplies the reflected moonlight color. The default values (R 0.8, G 0.9, B 1.0) produce a slightly cool blue-white tone characteristic of real moonlight.
Red component of the moon color tint. Range: 0.0–1.0.
Green component of the moon color tint. Range: 0.0–1.0.
Blue component of the moon color tint. Range: 0.0–1.0.
Stars
Star Map Settings
Star Map Settings
Alpha Piscium renders stars from a real star catalog. These settings control how the catalog data is interpreted and displayed.
Overall brightness of all stars. Range: 0–16. Higher values make faint stars more visible and the night sky more dramatic.
Extra brightness boost applied only to the most prominent catalog stars. Range: 0–8. Creates more realistic apparent size variation between bright and dim stars.
Gamma/contrast applied to the star brightness distribution. Range: 0.1–2.0. Lower values compress the range, making faint stars more visible. Higher values increase contrast between the dimmest and brightest stars.