A couple of weeks ago I spend 4 days in a local elementary school with an inflatable planetarium.  I did shows during the day for all of the classes in the school (20 shows in all) and then did brief, 12 minute public shows in the evenings(18 of those).  In all, 600+ people saw a show in the dome.

Mac Desktop on Portable Planetarium Dome
After a couple of the public shows, I gave the audiences a peek behind the scenes. Here's my Mac desktop on the dome, warped by the mirror.

I have to say, I had an amazingly good time – the teachers and students were wonderful – and the kids had amazing questions.  But I’ll talk about that another time…  What I want to talk about today is the geeky end of the whole thing – and how it’s possible to set up a portable, inflatable digital planetarium.

The Dome

The dome, made by Go-Dome, is inflated much like a bounce house at a fair, except that it has no floor – it just sits on the floor of the room it is set up in.  You roll it out on the floor and it inflates in a couple of minutes.  The kids (and adults) really enjoy squeezing through the airlock to get inside.

Inflatable, Portable Planetarium set up in the elementary school.
The dome set up and ready for an audience.

The Projection and the Mirror

The projection technology I used is very cool.  It was originally developed by Paul Bourke, an Australian academic who works on 3d, dome projection and related ideas. The problem with digital projection in domes traditionally is that it either requires many projectors, blended together, or a very very expensive custom fisheye lens.  Paul realized that a single projector aimed at a 1/2 hemisphere mirror would cover almost the entire dome.  He then figured out the warping process that’s necessary to pre-distort the images to be projected, so when the are distorted by the curvature of the mirror, they come out right on the dome.   If you’d like to know more about this process in detail, check out Paul’s pages on spherical mirror dome projection.

I used a commercial implementation of Paul’s technology from Discovery Dome.  It encloses the  (fragile) mirror in a case which opens up.  The projector goes under the mirror facing forward, the light bounces off a flat mirror, and then off the spherical mirror on to the dome.  This keeps the projector out of the way….

Inside the inflatable mirrordome planetarium
Here's a look at the back of the dome - the funny looking thing towards the upper right is the spherical mirror setup. I'm to the right behind the computers.

The Computers

All of the images were generated from my MacbookPro, and I used a Macbook for control of certain things on the projection computer – more on that later.

The software I ran is an open source project called Nightshade, which is a fork of Stellarium specifically for use in domes.  By using a combination of live keyboard commands in Nightshade and running scripts written in Nightshades scripting language that I wrote, I had a very powerful and flexible planetarium that I could use interactively to take the shows where ever the kids questions lead.

That interactivity is where the 2nd computer came in – running scripts in Nightshade requires going several levels deep in a menu and taking more time the I wanted.  That is for all the scripts except the demo which runs from a keyboard shortcut.  So I wrote a shell script to give me a menu of my scripts and rename whichever one I wanted to run “demo.sts.” so I could run it with the hotkey.

The only problem is that when Nighshade is running, it takes over the displays completely – no way to have a terminal open to run my script in.  So I brought the Macbook – I used it to SSH into the Nightshade computer and run my shell script.  So I used the Macbook to select scripts, and the MacbookPro right in Nightshade to do everything else.

It’s kind of a hack, but it worked great.

Try it yourself

By the way – If I’ve gotten you interested in trying to do something like this on your own, you can home build your own planetarium.  I particularly like the instructions on the Microsoft WorldWide Telescope site. You can use this with Nightshade, or with the MS WorldWide Telescope – which I highly recommend.  In fact I would have used it in my shows if I had known about it at the time – it’s not a replacement for Nightshade (in my view) but a great compliment to it, and an amazing piece of work.  Lots of fun on your desktop to – you don’t need to run it in a planetarium.

Me in front of the Go-Dome inflatable planetarium
Here I am in front of the dome at the end of a long day of shows.

On to the Planets

Now I’m moving on to another astronomically related projection project – I’m creating giant projections that will accompany the Portsmouth Symphony Orchestra’s performance of Holst’s suite The Planets.  The Performance will be on June 6th at The Music Hall in Portsmouth, NH.  I’m going to be blogging about my design process along the way, so keep an eye out for that, coming up soon.

Planetariums are magical places for many of us – I’d love to hear stories about your first or most memorable planetarium visit in the comments!

  • Wow! That’s so COOL!!! I want one of those in my house! Could you sleep inside one of them?

    • admin

      yep – you can sleep in one – it’s about 15 feet across which is quite spacious inside – we can put 20 kids and 3 or 4 adults mostly laying on the floor for a show…

      check out that link to the MS WorldWide Telescope page – you really can build that dome yourself and have one at home – the only real difficulty is ceiling height.

      It’s so much fun!

      Andy

  • Wow! That’s so COOL!!! I want one of those in my house! Could you sleep inside one of them?

    • admin

      yep – you can sleep in one – it’s about 15 feet across which is quite spacious inside – we can put 20 kids and 3 or 4 adults mostly laying on the floor for a show…

      check out that link to the MS WorldWide Telescope page – you really can build that dome yourself and have one at home – the only real difficulty is ceiling height.

      It’s so much fun!

      Andy

  • Nice article! Kids love planetariums, and it is a great thing to share with them. We have been touring portable planetariums to schools for more than twenty years and have shared the same experience you describe with thousands of schools. We call our program Skydome, and since we try to make it available to an entire school in one day we use a larger dome than yours. Ours is thirty feet across and allows up to 100 kids per show.
    I am intrigued by your projector! Very cool take on this problem. We use a Digitalis projector which works well with the larger dome. We looked into the Godome and though it is a great design, we felt it was too small for our needs.
    Isn’t it cool to see the kids faces and the awesome looks inspired by the night sky?

    • admin

      It is VERY exciting to see how engaged and “starry eyed” the kids get when they just see the inflated dome, and then to have that build from there as the stars come out and they start to learn.

      They system I used is borrowed – so it’s what they had… but it does work very well.

      I think that if I had the money and I was going to buy a system for the sort of work you do, I would be likely to go with either the Digitalis system or the SkySkan Definity system – Definity is awesome but expensive. Digitalis is great, and based on Nightshade – the same software I used for this outing – it works very well, but it doesn’t have the flexibility of the Digital Sky 2 software that runs the Definity systems – with that you can actually fly just about anywhere in the universe.

      From looking at your website it looks like you’re using a starlab dome with your Digitalis projector. If so, I’d take another look at GoDome They make up to 9 meter domes (29.5 ft). The entryway also saves a HUGE amount of time in load/unload rather then the starlab tunnel. I haven’t used one, but if I was going to buy a new GoDome, I’d get one with 3 or 4 tubes around the base to get the spring line further up off the ground (and above the kids heads – that way you really get the full hemisphere to project on. I’ve always felt the image was somewhat compressed vertically with the one I’ve used (that doesn’t have the tubes).

      Thanks for your comments!

      Andy

  • Nice article! Kids love planetariums, and it is a great thing to share with them. We have been touring portable planetariums to schools for more than twenty years and have shared the same experience you describe with thousands of schools. We call our program Skydome, and since we try to make it available to an entire school in one day we use a larger dome than yours. Ours is thirty feet across and allows up to 100 kids per show.
    I am intrigued by your projector! Very cool take on this problem. We use a Digitalis projector which works well with the larger dome. We looked into the Godome and though it is a great design, we felt it was too small for our needs.
    Isn’t it cool to see the kids faces and the awesome looks inspired by the night sky?

    • admin

      It is VERY exciting to see how engaged and “starry eyed” the kids get when they just see the inflated dome, and then to have that build from there as the stars come out and they start to learn.

      They system I used is borrowed – so it’s what they had… but it does work very well.

      I think that if I had the money and I was going to buy a system for the sort of work you do, I would be likely to go with either the Digitalis system or the SkySkan Definity system – Definity is awesome but expensive. Digitalis is great, and based on Nightshade – the same software I used for this outing – it works very well, but it doesn’t have the flexibility of the Digital Sky 2 software that runs the Definity systems – with that you can actually fly just about anywhere in the universe.

      From looking at your website it looks like you’re using a starlab dome with your Digitalis projector. If so, I’d take another look at GoDome They make up to 9 meter domes (29.5 ft). The entryway also saves a HUGE amount of time in load/unload rather then the starlab tunnel. I haven’t used one, but if I was going to buy a new GoDome, I’d get one with 3 or 4 tubes around the base to get the spring line further up off the ground (and above the kids heads – that way you really get the full hemisphere to project on. I’ve always felt the image was somewhat compressed vertically with the one I’ve used (that doesn’t have the tubes).

      Thanks for your comments!

      Andy

  • Yeah, we used to use Starlabs when we started but they were just not large enough so we contracted with a private company to make similar but much larger ones specifically for us. If Godome does make ones as large as you say we might have to look at those when the time comes to replace ours (as they wear out).

    Thanks for the info!
    Geoff

  • Yeah, we used to use Starlabs when we started but they were just not large enough so we contracted with a private company to make similar but much larger ones specifically for us. If Godome does make ones as large as you say we might have to look at those when the time comes to replace ours (as they wear out).

    Thanks for the info!
    Geoff

  • admin

    Oh, I see.

    The godome surfaces work very well for digital projection – I think it’s quite a nice product.

    I would not get the light weight version though – extra weight = extra durability.

    Andy

  • admin

    Oh, I see.

    The godome surfaces work very well for digital projection – I think it’s quite a nice product.

    I would not get the light weight version though – extra weight = extra durability.

    Andy

  • Ada Abiaka

    great stuff. I dont know much about planetariums. My company has an annual science interactive exhibition for kids. This year we would like a planetarium because our theme is on light, optics and vision. Its very nouvell where i live. Need advice that is easier for non techie to understand. check us out on http://www.inspirekidstoday.org
    Ada

    • Hi Ada,

      I’m not sure how to help you – unfortunately setting up a planetarium is either expensive, technical or both….

      Best thing would be to find a company in your region that travels with a portable dome system and could bring it to your event…

      If you tell me where you’re located, I might be able to get you in touch with someone…

      Andy

      Sent from my iPad