Interactive Earth-Moon-object space

Purpose: makes the three-dimensional geometry behind sky direction and distance tangible. Display: freely centred, right-handed equatorial J2000 coordinates (+X to the vernal equinox, +Y to R.A. 6 h, +Z north), with textured Earth and Moon, planets, Sun, nominal current object positions, and the real bright-star sky in the current viewing direction. Earth and Moon phases follow the propagated Sun geometry; faint secondary illumination shows Earthshine on the Moon and moonlight on Earth while retaining subdued surface detail on the night sides. Read: choose Earth, Moon, Sun, a planet, or a current object as the centre; drag to rotate, use the mouse wheel or buttons to zoom from Earth scale to the outer Solar System, and select an object to open its ephemeris. The Earth-north and Sun-direction arrows can be switched separately. The three-axis gizmo and central reticle show orientation and aim; the X/Y/Z controls move that aim through space relative to the selected centre. The movie interpolates continuously between six-hour calculation nodes, has separate Start, Pause, Faster, Slower, and Reverse controls, and keeps its adjustable start and end limits when the calendar time changes. Loop restarts it. Zoom-out reaches at least 100 AU (beyond Eris) and expands farther when a current object requires it.