h a l f b a k e r yAssume a hemispherical cow.
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He proposed it in May 13, 2005. But when did he do dat. |
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Ah, but [nineteenthly], yours doesn't seem to project the
constellations on the walls. This does. |
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Obligatory misreading: anatomically. |
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Gastronomically correct disco ball.... all sorts of healthy food orbits at a safe distance the dreaded black hole of McDonald's and KFC's toxic muck. |
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//the dreaded black hole of McDonald's and KFC's
toxic muck.// |
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After eating a McDonald's, I feel cheap and dirty. It's
fantastic. |
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I would think this was worth doing twice. |
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This is going to be challenging to make. |
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If you want Orion (for instance) to be two metres tall
on a wall 3 metres away from the ball, and if you
allow an error of 1cm in placing each star, the mirror
for it will have to be accurate to within 0.2 degrees. |
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// but [nineteenthly], yours doesn't seem to project the
constellations on the walls. // |
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It's clear if you read the annotations that the intended
effect was the same, though it wasn't stated as clearly,
and if implemented exactly as described would not have
worked. Putting reflective paint on a sphere would have
resulted in diffuse reflected light, not points, and
painting the constellations accurately on the ball would
have resulted in distorted constellations. |
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For this idea to work really well, you actually want
almost a point light source and slightly concave mirrors
to refocus the light back to a point when it hits the walls.
Of course in a square room, the distance from ball to wall
or ceiling varies, so the focus will be off a bit, but could
be improved slightly over the large dots that flat mirrors
on a disco ball create. |
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To make this thing with the required degree of accuracy, one would use the method described in the <link> for DIY solar furnace making. i.e. each mirror is mounted on screws, and each mirror in turn is tweaked to point at the required point. I suppose you start with a planetarium projector to indicate the points of the constellations on your walls. Then you aim each mirrorball mirror in turn at one of the constellation stars. For particularly bright stars, aim two mirrors at the same spot. |
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You would do this with just a hemisphere, which will reflect your spotlight source onto the entire room interior. This also allows for access to the screws on the inside. |
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Repeat exactly the same with the second hemisphere, before finally affixing them together. |
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Yes the fact that the mirrors are not all in the same spot will mean the pattern varies with distance from the ball. But I would think that in a normal, approximately spherical room, the effect would be minimal, and you could simply calibrate the ball to your room size. |
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//a normal, approximately spherical room// -
excellent! Now I want to see where [pocmloc] lives. |
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Note that if you placed this outdoors next to a building, during sunny days the starfield would move along the building ...as if the whole Earth happened to be rotating?! |
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Simple version: chrome-plated sphere with shrink-wrap transparency: black, with little clear spots. |
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Idea: 3D-print the whole thing (or each hemisphere.) The resulting sphere is covered with precisely-angled facets. Then coat with adhesive, and hand-place the mirror-chips onto all the sticky facets. |
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Or: 3D-print the master mold (the concave shell.) Then use it to vacuform many, many replica earth-hemispheres. Then sell them as a kit, along with a big bag of mirror-chips and a roll of double-stick tape. |
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Half-price for the Northern Hemisphere only! :) |
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Ball with internal laser source and fiber-optic cables to lenses on surface in a precise pattern to yield and accurately projected image (true colour can be attained by using RGB laser and filters on lenses). Spaces between the lenses occupied by PV material. |
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Shine a light at this ball and the power is converted to run the laser, which then projects fine points of light. Of course the light will be below the level at which it could cause retinal damage by limiting power and/or slight defocus. |
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Since this would be a ball that hangs from the ceiling and requires a light to be pointed at it, causing spots to be projected on the walls, I'd say it qualifies as a disco ball, though an oddball version. |
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I have just realized that the mirror version of this idea
would result in distorted constellations no matter what.
Think of the angles of incidence and reflection from a single
point source of light at various points on a sphere in front of
the light source. |
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