Personal Planetarium?
January 6, 2017 11:08 AM   Subscribe

I'm looking for a home planetarium that will fill a room with stars. I'd like something that projects onto the walls and ceiling, and something that's bright enough so that the stars are visible on a wall 10 feet from the device. The star themselves don't need to be correctly placed, I'm going for the feel of a stary sky rather than being able to identify specific stars and constellations. At the same time I do not want any constelation lines, planets, or really anything except the stars themselves.

This will be used in an art installation, where I want ~5 people at a time to be able to lie on the floor and have the feeling that they are lying in an open field under a stary sky. The products I've found so far seem to fall into one of two categories: relatively expensive devices that project accurate start maps only on the ceiling or inexpensive devices that do project on the walls and ceiling, but are badly reviewed, don't throw much light beyond a few feet, and have blurry stars. Ideally I'd like something more like the second link, but one that is higher quality.
posted by Maastrictian to Science & Nature (12 answers total) 27 users marked this as a favorite
 
Maybe something like a laser light projector? You might be able to get one cheap right now, since a bunch of versions are advertised for "decorating" your house during the holidays. You'll avoid the blurry lights issue, but it may be tough to do an entire room.
posted by troytroy at 11:15 AM on January 6, 2017 [2 favorites]


You could get some sort of rigid hemispherical plastic object (like a bowl), poke a bunch of holes in it with an awl, put it on top of some sort of cylinder, and put a very powerful light inside it.
posted by showbiz_liz at 12:09 PM on January 6, 2017 [1 favorite]


Ooo, Pinterest has lots of tutorials for homemade planetarium projectors, and if you make your own, you can use as powerful a light as you can get your hands on!
posted by showbiz_liz at 12:13 PM on January 6, 2017 [3 favorites]


I have the Uncle Milton Star Theater Pro, which is similar to the Homestar that you posted. I remember it being a midpoint price-wise when I picked it up but I think they're harder to find and more expensive now. I'm very happy with it, the image is large and clear. It covers the ceiling of my bedroom pretty well, but as you mentioned, doesn't reach the walls. You can also get a pretty wide range of replacement disks for it at Miller Engineering, which I do recommend. They're much better than the ones that come pre-packaged.
posted by Phobos the Space Potato at 12:16 PM on January 6, 2017 [1 favorite]


Borrow or rent a computer projector if you don't have one. Download Stellarium (it's free) and project away.
posted by Weftage at 12:58 PM on January 6, 2017 [1 favorite]


It's a little more work, but we did either the Toysmith Nightscapes or a remarkably similar product in our bedroom. It's a relatively low-res overblown projection system (grain of wheat lamp with a transparency sky map), a set of several different sizes of acrylic rod, for making different brightness stars, and glow in the dark paint.

Project the sky on the ceiling, use the rods to put glow in the dark dots on the various different size dot stars, do some random stippling for the Milky Way, and, clean up what you spilled, and...

What it doesn't capture very well is the different color of different stars, but it's still pretty damned cool to look up at night and see the summer sky.
posted by straw at 1:26 PM on January 6, 2017


I wonder if there might be a simpler solution - could you put dots of blacklight paint on the walls and hook up a blacklight bulb?
posted by rebent at 2:10 PM on January 6, 2017


So kinda thinking this out as I go, hopefully this doesn't get too windy and confusing: In order to get a clear image over a longish distance, you need to get a narrow beam of light.

You could do it by focusing the light output with lenses, like in an actual projector, but then you are literally reducing the angle of the beam. This is pretty much what the nice planetarium gizmos are doing, and why they only project in one direction.

You could plunk a colander over a light bulb, but since the unfocused light rays are scattering through the holes every which way, the sharpness will drop off very quickly as the distance to the wall increases. This is why the cheap planetariums suck. If you make the hypothetical colander holes really tiny, you have reduced the amount of scattering so the output will be sharper (this is how squinting and pinhole cameras work) but you'll need a more powerful light source to get the same brightness.

I don't know how lasers work and I'm not even going to try, but they are by definition extremely narrow beams of light. Those holiday decor ones look pretty affordable, but from your question, it doesn't sound like they'll get the look you're going for. Also apparently they only managed to create white lasers in a lab two years ago, which is pretty cool but I don't think they've made it to Home Depot yet.

Long story short, I don't think you will easily be able to get a good cheap planetarium that projects as far as you need in multiple directions. Depending on financial and technical resources, space limitations, and how strict your output requirements are, I might try to go about this a few different ways.

- Get a single projector and figure out how to bend the rays to project over a wider angle. One of showboat_liz's pinterest links goes into a lot of detail on how to build a geodesic planetarium and links to a reaaaaally extensive site and FAQ on wide-angle projections. Looks amazing but also complicated.

- Get multiple projectors and line them up carefully. This seems technically the easiest, especially if you can scrounge projectors from somewhere. One per wall would be ideal, otherwise, you'll get some distortion in the corners. If you use digital projectors, that might be something you could correct for in the image. If you have old analog projectors, maybe there's some way you could hack the Miller Engineering projection discs to work with them.

- It's simple so you might as well try the colander-over-a-lightbulb method. Actually, try multiple colanders with sections blocked out, because then you could arrange them closer to the walls and get by with larger less precise holes and less powerful light sources. I'm skeptical that one powerful central unit would have enough throw, also would be afraid of burning your project down, but multiple ones might do the trick.

- Go at this from the other direction. Poke your stars into big sheets of opaque paperboard or plastic, mount them so they cover all the walls and ceilings with no gaps, and stick some LEDs to illuminate them from behind. This makes my hands hurt thinking about doing it manually, but would be easy if you had access to a laser cutter.
posted by yeahlikethat at 2:22 PM on January 6, 2017 [5 favorites]


I've used GloNation paints before, and the blues and greens do stay bright for several hours. They no longer carry the neutral red and yellow (less than 15 minutes glow for the red), but you might get some mileage out of the others.
Do start with a white background. When you are tired of it, paint over it.
I would not bother with regularly available paints because of the quick disappearing effects.
posted by TrishaU at 2:35 PM on January 6, 2017 [1 favorite]


I've been trying to do something similar to this for a friend's wedding and it's surprisingly challenging! I think the laser light projectors such as the one linked by troytroy above use red and green solid-state laser diodes, rather than filtered white light, so they are pretty much stuck projecting red and green "stars" and there's no easy way to change that. (In other words, there's nothing you can easily rip out of them to make them just project white stars.)

Some stores sell a version that's all blue, rather than red or green (there's also solid green available, I think), which might feel a little less Christmasy, but it's pretty obviously not the same cold blue-white of actual stars or from a conventional planetarium bulb. Depending on how accurate you need to be, it might or might not work.
posted by Kadin2048 at 3:25 PM on January 6, 2017


Ebay has many, many options.
posted by moonlight on vermont at 7:01 PM on January 6, 2017


I'd try for the opposite: instead of projecting lights from the ground, put actual lights on the ceiling. I'd start with a heavy dark cloth, or even something solid like plywood, with pinprick holes in it. Put a source of light behind each hole (I'm thinking a Christmas-style strand of lights with the extras removed, or LEDs, or a regular light bulb that is itself in a container that blocks most light except one small opening).
posted by Questolicious at 7:19 PM on January 6, 2017 [1 favorite]


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