Ricky Spears’ Blog
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28
Jul

How to Build a Home Planetarium with Cardboard

About ten years ago I was really into astronomy as a hobby. I don’t do very much stargazing these days, but it is a wonderful hobby that I will probably invest more time in later in life.

Since I am a Christian, I was especially interested in studying Ancient Hebrew Astronomy. I found 3 excellent books on the subject that I used for most of my study:

There are more books available, but these are the ones that I used primarily.

At that same time, I was teaching a 5th-grade Sunday School class. I wanted to teach them these fascinating stories from Hebrew history using the stars. The only problem was that the class met at 10:oo AM on Sunday morning instead of 10:oo PM.

My wife had given me a toy planetarium for Christmas the previous year. I was going to use this in the classroom, but everything got all skewed when it projected on the flat ceiling and walls. I really needed a dome to use it properly.

I couldn’t find a reasonably priced dome that would fit my needs, so I decided to create my own. There were only a few students in the class, so it didn’t need to be very big. I thought that a 6-foot diameter would work well. I had access to some scrap cardboard from work that was white on one side, so I decided to use this as my main material. I would cut out 64 cardboard panels and tape them together to make my dome. It would be made in 4 sections that could collapse and nest together for easy storage. It would have extra tape on the sides of each section and I would use binder clips to hold the sections together.

I had a pretty good idea how to make it, but I didn’t have any idea about what the dimensions on each cardboard piece should be. I hadn’t used trigonometry since I was in high school, but I knew that was the tool I needed. I checked out a trigonometry book from the library and set about to teach myself trigonometry all over again. Although I must admit that I’ve probably forgotten most of it again now, at that time, I’m confident that I understood it much better than when I was in high school because I had a problem to solve with it.

I wrote some formulas that would help me determine the dimensions for each trapezoid, and the dimensions for the triangles near the top. I put these in a paper I called Formulae for Panelized Hemisphere Construction (PDF). It’s been 9 years since I wrote that paper, and I’ve never shared it with anyone until now. If you have ever wanted to make your own panelized dome, I hope this helps. Because it has been so long, I doubt that I can answer many questions. If you have any comments, or you actually use this information for something, I would appreciate it if you would let me know in the comments.

Here are a few pictures of the completed dome in use:

Cardboard Planetarium 1
This is the view of the fully assembled dome as it sat in the corner of our classroom.
You can see the panels clearly, and you can even see the binder clips that held the sections together.

 

Cardboard Planetarium 2
The whole dome rested on a wooden frame made from inexpensive 1×2 lumber.
The church was Bethany Baptist Church in Thomasville, NC, so I called it The Bethany Planetarium.

 

Cardboard Planetarium 3
You can see the projector and the dome in this view. I set the projector on a speaker cabinet
which brought it up to the perfect height.

 

Cardboard Planetarium 4
I didn’t have any way to project other information on the dome, so I printed the constellation
charts from on of my books, blew them up, taped them together, and then taped that to
the support frame. All the students were on one side and they could see this. I used a
laser pointer to point out stars in the picture and on the dome.

 

Cardboard Planetarium 5
This shot shows the projector and the zenith of the dome.
Everything fit together quite nicely.

 

Cardboard Planetarium 6
I couldn’t find any pictures of the collapsed dome,
but I did find one picture that had it sitting in the corner.
The four sections would nest, and and fold up to fit in a small area.

The planetarium sat unused in the corner of my home office for years. A few years ago, I donated it to the Forsyth Astronomical Society. I’m not sure how they are using it today, but hopefully it is still helping to educate some people on the beauty of the night sky.

If you live in a location with a lot of light pollution, building a home planetarium can be a great project for you and your children, and a great way to use that toy star theater the way it was meant to be used.

 

 

15 Responses to “How to Build a Home Planetarium with Cardboard”

  1. 1
    ivie Says:

    wow.. this is awesome. I’m looking for how to make my own planetarium and I find our site. this is a great idea.

  2. 2
    ivie Says:

    sorry I mean you not our…

  3. 3
    rickyspears Says:

    Ivie – Thanks for stopping by! If you build one of these, let me know how it goes!

  4. 4
    snd_jin Says:

    It’s so great!!!!!!!!!!!!
    I’m looking for a way to make
    a portable planetarium, smaller one
    like a lamp.
    I’ve never thought one could make their own planetarium before, but you did.

  5. 5
    Jack Says:

    I plugged your formulae into OpenOffice spreadsheet, my results are way off, but all numbers are correct, any suggestions? I am looking for ways to make a 10-12 foot dome. This could be usable if I can get the formulas working.

  6. 6
    rickyspears Says:

    Jack – As far as I know, the formulas are correct in my document. If you can send me your spreadsheet, or at least send me the formulas as you have them in your spreadsheet, I can see if I can find the error.

  7. 7
    Jack Says:

    Sorry about delay getting back to you.
    Here is the first formula as entered into the spreadsheet;
    =SIN(90-(90/D5)*0)*D3
    where D5= 4(lat sections)
    and D3 = 36 (Radius)
    The result of this calc is 32.1838798896

    This is the second version of spreadsheet entry and I am still wrong. Guessing that OpenOffice is doing the order different maybe???

  8. 8
    rickyspears Says:

    Jack – When I wrote this I was just using a basic calculator with trig functions and not a spreadsheet program. However, I just entered this formula into both Google Docs and Excel and I got the same result you did. It took me a few minutes to realize that the trig functions all assume the angle is in radians instead of degrees. So, since my formulas assume degrees, you’ll need to use the RADIANS() function to convert those results to degrees. So, the formula in a spreadsheet would become
    =SIN(RADIANS(90-(90/D5)*0))*D3
    The result of this is correct: 36.

    I hope this helps! Good luck!

  9. 9
    Jack Says:

    OK, that worked! However, when you change C to the other three values ou end up with:
    35.82
    35.30
    34.44
    Sorry to be such a pain! I like math but could never get my head around it so resolving the problems here are difficult to say the least! Once I get the spreadsheet working I will send it to you so you can include it here is you so please.

  10. 10
    rickyspears Says:

    Jack – I think you’ve got a problem in your formulas for R1, R2, and R3. I’ve set these up in a Google Docs Spreadsheet and it gives the same results I have in my paper:
    https://docs.google.com/spreadsheet/ccc?key=0AgVsF7Mwf0vudFdKYzFnZTg3VXdHSUtqSU16WWQtaHc

  11. 11
    Jack Says:

    Ok, found my problem! I was trying to use the Longitude number, funny thing is in the first calc it came up with the same answer so I never checked my formula.

  12. 12
    Jack Says:

    I worked up a spread (of sorts) in Open Office. Available to you if you want it.

  13. 13
    rickyspears Says:

    Jack – I’m glad you got that all figured out! If you’ll send it to me at rickyspears at gmail dot com I’ll put it in Google Docs or SkyDrive, link to it from this post so others can find it and ue it, and credit you as the developer.

  14. 14
    Jack Says:

    Just sent you the spreadsheet. Hope it works for you.

    Do you know if it would be possible to change the shape of the structure from a half sphere to more of a bowl shape? flattened than what it is now?

  15. 15
    rickyspears Says:

    Jack – Man, I hate that it has taken me over four months to respond to this. I’ve had a very hectic summer and fall and I’m just now getting to a bunch of emails and tasks that I had put on the back burner.

    Excellent work on the spreadsheet! I’ve uploaded your spreadsheet to my Google Docs so people can find it here: https://docs.google.com/spreadsheet/ccc?key=0AgVsF7Mwf0vudHJpYy1BYzY1MEJCdFlsVVVrd3RWbFE
    They can then download it to work with it.

    By the way, for other’s benefits, here are the notes you sent in the email when you sent the spreadsheet:
    ——————–
    Quick explanation, if I can remember, Enter variables in blue cells. Red cells are weights of various components. Probably should be reweighed by each user. The clips are the black and silver paper clips like you used in your construction. I wanted to have an idea how heavy the entire structure would be, so I needed to included clip weight. The only thing I did not account for was the ‘flanges’ on each panel. I would have loved to have the program redraw each panel but I am not savvy enough in spreadsheets to do that.
    ——————–

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