RISE_HEIGHT_RADII

How high a rise stands, as a fraction of the body's own radius.

0.063 puts the eye 110 km over Luna, which is where the Apollo 8 frame was taken from — low enough that the horizon is a curve rather than a limb, high enough that the parent clears ground the geology has not been built yet. Relative to the radius rather than a fixed height, because the same fraction has to make a picture on Phobos (710 m up) and on Ganymede (166 km).

devtools/src/observatory.ts:315