The Clouds Appearance control contains settings for the on-screen appearance of an object's clouds.
The checkbox on the left of the control determines whether the cloud layer of the object is displayed. Turning off the visible atmosphere can allow the user to see the surface more clearly.
The color setting on the right of the control sets the color of the clouds. For known terrestrial planets in the Solar System, including Venus, Earth, and Mars, the Default color of the planet's atmosphere is set by the Universe Sandbox database to match the known appearance of these planets. For other terrestrial planets, the atmosphere color is randomly generated.
The Clouds Appearance control is located in the Layers section of the Appearance tab of an object's properties panel.
Expanding the Clouds Appearance control reveals a number of settings related to the cloud speed and appearance.
When set to Simulated, the Speed at Equator of each cloud map will be simulated based on the object properties. When set to Custom, the user can set the speed of each cloud map.
Map 1 or 2
An object's clouds are represented graphically by two overlapping cloud maps, to create a variety of patterns. The user can select from several different map options for each of the two clouds maps, or hide the map completely by selecting "None".
The Rotational Period of a cloud map represents the time needed for the map to rotate once around the object. The Rotational Period, P, is related to the Speed at Equator, v, by
where R is the Radius of the object.
Speed at Equator
The Speed at Equator of a cloud map represents its tangential speed across the surface, measured at the equator. When the Cloud Speed is set to Simulated, this speed will be simulated based on the object properties. The Speed at Equator, v, is calculated by
where ΔP is the difference in pressure between the equator and pole (estimated from the Surface Pressure and the Minimum and Maximum Temperature of the surface), Δy is the distance between the equator and pole (equal to one-quarter of the object's circumference), ρ is the Atmosphere Density, and C is the Coriolis factor, equal to
where Ω is the object's rotation speed (calculated from the Rotational Period) and φ is the latitude where the Coriolis effect is measured, in this case 45°.
At lower object rotation speeds, this model will predict higher and higher cloud speeds. The maximum allowed Speed at Equator for clouds is capped at the atmosphere's Speed of Sound.
The cloud Coverage represents how much of the surface is obscured by clouds. A Coverage of 0% will produce no visible clouds, while a Coverage of 100% will almost completely cover the surface.
The cloud Opacity represents how opaque the cloud layer is. An Opacity of 0% will produce no visible clouds, while an Opacity of 100% will produce thick, opaque clouds.