VISUAL MODEL · SIZE AND DISTANCE
Why one view cannot show every true scale
Compare Solar Time's readable overview with actual-size mode and see why one scale cannot show everything.
The physical ratio is larger than a viewport
Earth's diameter is about 12,742 kilometres, while its average distance from the Sun is about 149.6 million kilometres. If Earth were drawn as a two-pixel disc, the corresponding Sun–Earth distance would extend far beyond an ordinary display. Making the orbit fit pushes Earth below one pixel, and including Neptune makes the mismatch stronger.
Textbooks and interactive models therefore separate body scale from distance scale. The important requirement is clarity: identify the adjusted view, provide a way to compare it with a more physical ratio, and avoid presenting decorative spacing as a precise measurement.
Normal view is a comparative diagram
Solar Time's normal view enlarges bodies and manages orbit gaps so the Sun, planets, and major moons remain selectable. It is useful for relative ordering, phases, composition, and parent–moon relationships. It is not a ruler, and a pixel gap in this mode should not be converted directly into kilometres.
Individual size controls also belong to this presentation layer. Enlarging the Moon or Europa makes surface detail and eclipse demonstrations easier to see without changing the astronomical radius stored by the model.
Actual-size mode exposes the disparity
Actual-size mode reduces artificial enlargement and moves spacing toward physical relationships. “Actual size” describes the ratio used by the visualization; it does not mean a monitor contains a literal kilometre-scale system. Projection, field of view, clipping limits, and minimum pixels still matter.
At maximum camera distance, a physically projected planet can cover less than one pixel. Solar Time then uses a point-like representation. The Sun has the largest minimum, giant planets a smaller tier, rocky planets another tier, and moons plus Pluto the smallest. This hierarchy preserves discovery without making every body equally bright.
LOD should change detail, not apparent size
A textured sphere is useful nearby but wasteful when it covers a fraction of a pixel. A point sprite is efficient far away. During the handoff, coverage and brightness overlap smoothly. Otherwise the body can collapse and then grow, or appear to flash when both forms are fully visible.
Lighting must participate too. A backlit sphere may be dark while a navigation point is bright. If the point ignores the sphere's visual state, approaching the body looks like a lamp suddenly switched off.
Try it in Solar Time
- Establish a baseline: press 0, pause, and note the order and orbital phase of three planets. Switch actual-size mode on and off. Those astronomical relationships should remain even though screen size and spacing change.
- Find the visibility floor: set orbit spacing to 100% and move as far back as possible. Compare the minimum point sizes used for the Sun, giant planets, rocky planets, moons, and Pluto.
- Watch a level-of-detail handoff: move slowly toward one selected planet. Its distant point should yield to the textured body without a sudden collapse, flash, or size jump.
- Test lighting continuity: repeat with a backlit body. The navigation point should fade with the body's visual state instead of remaining an unrelated bright marker.
Sources and further reading
- NASA Science — Solar System Sizes
- NASA Science — Solar System Facts
- Solar Time — From clock time to planetary motion