Note: This documentation is preliminary and subject to change.
This document describes how to build a planetarium for use with
The planetarium provides schools and other groups with a great way to
visualize the panoramic view of the universe provided by WorldWide Telescope.
The planetarium described here is just under 12.5 feet in diameter, and just
9 feet tall. So the first step is finding a suitable location for it! The
materials used are not suitable for an outside location, so the location should
be inside, level and dry. Alternative measurements are given for a smaller (9
feet diameter) planetarium, though all the images
in this document are for the 12.5 feet model. Measurements are given in inches
as this is the most used unit for packing materials and particleboard, which are the
main construction materials used - 48 inch wide corrugated cardboard, and 48
inch wide particleboard paneling are both easy to come by. The Dome Specification Utility
can be used if metric measurements are preferred.
One of the most interesting features of the dome is that it is tilted at an
angle of 20 degrees. This makes construction a little more complex, but the
design gives a much better experience. The idea is that students will feel they
are traveling in a space ship towards a planet such as Saturn, which
would not be the case if the view was vertical. The tilt also gives room for a
reasonable pair of doors, and room for the projector and mirror, without excessive
height. The cost to this though is that constructing the dome support is as
involved as constructing the dome (a geodesic half-dome to be precise) itself.
Costs for materials vary, however a reasonable budget for the dome and
support components is US $700.00 at 2009 prices. In addition to this a spherical
mirror is required, optionally a flat secondary mirror, and a suitable projector. Tools are not included in our
budgeting, as they are common household tools that many teachers and parents
will own already. A laptop running WorldWide Telescope is obviously not included
in the budgeting either.
Note that a number of the tasks involve the use of cutting tools and power
saws, so responsible adult involvement in the project is essential.
Table of Contents
Construction of the Dome
Adding Ventilation and Power
Adding Seating and Carpeting
Setting up the Projector and Mirrors
Run WorldWide Telescope
- Construction of the Dome Support
Construction of the dome, and the dome support can largely proceed in
parallel. To construct the dome support, go through the following procedure:
- Purchase the necessary materials:
Assemble the necessary tools:
- 5 sheets of particleboard, or plywood, 96 inches by 48 inches.
- 17 feet of 2 x 3 inch wood.
- 20 feet of 2 x 2 inch wood.
- 120 wood screws (1 or 1.25 inch).
- 20 heavy duty clips to attach the dome to the support.
- 10 lengths of 1 x 1.5 inch wood, each piece exactly 48
- Two hinges and one handle per door.
- Black 2 inch wide tape.
Understand the shapes involved. Both the dome and dome support are based on a decagon - 10 sided figure - shown in the following diagram:
- Miter saw, or compound miter saw.
- Portable circular saw.
- Hand saw.
- Safety goggles and masks.
- Matt black paint.
- Chalk line, or long measuring rulers.
- Other tools may be helpful: files, screwdrivers, planes, clamps, saw
horses, and so on.
Cut out, or have cut out for you, the 10 side panels in 0.5 inch
particleboard or plywood. The 10 panels are:
The dome is a decagon - each side is 48 inches.|
inside angle is 144 degrees.
The front to back diameter is 147.72
The side to side diameter is 155.32 inches.
After tilting 20 degrees the plan view of the support becomes an
elliptical, rather than regular, decagon. The top edge of each panel is 48 inches, but the widths of the
other panels vary - 48 inches for the rectangular panels. but 47.02 inches
and 45.4 inches for the angled panels.|
The dome support profile.|
Lightly sand and smooth the edges of the wood.
Cut out 20 wooden connecting blocks for the panels, from 2 x 3 (or
Because of the tilt, the blocks are not all exactly the same size. The
thickness of the wood is not that important - it is
the angles that are critical. The more accurate you can cut the angles the
less adjustment will be necessary when the dome support is matched to the
dome. Most miter saws will not cut at such an acute angle as 17 degrees, so
first make a template block with a cut at 73 degrees using a miter saw,
then to cut the 17 degree angle clamp the template block in place,
carefully place the actual block, and then a 90 degree cut will give the
desired result. Note that the two cuts on each block need not meet at an
exact point, though they can. A short flat section between the two angled
cuts is not a problem. With a simple 10 inch miter saw block widths should
be chosen that the saw can cut right through - which limits the thickness to
2.5 inches or so. A compound miter saw will give greater flexibility.
- 1 at 48 inch by 12 inch rectangle.
- 2 at 47 inch base, with one side at 12 inches and one at 21 5/8 inches.
- 2 at 45 3/8 inch base, with one side at 21 5/8 inches and one at 37
- 2 at 45 3/8 inch base, with one side at 37 1/4 inches and one at 52
- 2 at 47 inch base, with one side at 52 7/8 and one at 62 1/2 inches.
- 1 at 48 inch by 62 1/2 inch rectangle.
Before starting on the angled cuts, cut the 2 x 3 wood into 10 inch lengths
(20 are needed).
Take one of the panels marked "Door" in the preceding images. Cut out
a rectangular door shape, and fit hinges and a handle on the outside. The
door will open to the outside, so there is no need for a handle on the
It is a good idea to take quarter of an inch off the bottom of the doors
before fitting them, to avoid scraping the floor when opening and closing.
In this case ensure there is the supporting 2 x 2 wood across the bottom of
the doorway (to block out the light) shown in the images below.
Block A. Eight of these are needed. After cutting them out mark them
with an "A", as the angles of all blocks are very similar.|
The exact angles here are 72.85 and 17.15 degrees.
Note the 73 degree template block has been marked and clamped to the
Block B. Eight of these are needed. Mark these with a "B".|
The exact angles here are 71.7 and 18.3 degrees.
Make a 72 degree template block to start with. Then cut out
eight B blocks.|
Block C. Only four of these are needed. Mark them with a "C".|
The exact angles here are 70.9 and 19.1 degrees.
Make a 71 degree template block to start with. Then cut out four C blocks.|
Using short screws (1.5 inch wood screws, or similar) assemble the dome
support by screwing one block low down on each panel, and one near but not
at the top (at least 1 inch short of the top of the shortest of the two
panels). Pilot holes for the screws should be drilled first, and the screws
drilled into place but not tightened to the max until the whole support is
Start by laying out all the pieces in place - panels and blocks - flat on
The door height will be more suitable for children than for adults. |
If a larger door is required consider adding an equal amount to the
heights of all the side panels.
order to have a full size door the whole structure can be raised by
making the lower side of the dome support higher than 12 inches.
However, to have a 6 foot door the lower side will need to be around 36
inches, adding a further 2 feet to the height of the planetarium.
Add a second door to
the other side of the dome support - to provide both an "In" and an
"Out", and a fire escape.
|Note the 2 x 2 inch wood used to
strengthen both the side of the door frame containing the hinges,
and across the bottom of the door opening. Use scraps of wood to strengthen
the hinges on the door itself.|
For a rectangular door, consider using a powered
circular saw to cut out most of the door, but use a hand saw to
finish off the cuts. For the rounded door shown in the picture, use
a hand held jigsaw to cut out the shape, after carefully drawing the
arc on the panel.
The rectangular door shown in some of the images
is quite short - due to height restrictions in the assembly area for
the prototype - which is the reason why the rounded door was made as
to make a little more headroom.
On the outside of the top edge of each panel screw in a length
of 1x1.5 inch wood (or similar) that is exactly 48 inches long. This should create a
ledge all the way round the outside of the dome support. Accurately align
the ledge with the top of the panels, but more importantly with the preceding ledges, so that
the supporting surface for the dome does not change height from the end of
one side panel to the start of the next. Start at the tall rectangular
panel, and using 3 screws per ledge, carefully work your way around the dome
Using a 2 inch diameter hole drilling bit (or similar) - drill out a grid of 3 x 4 or
4 x 4 holes to be used to vent the planetarium.
Note the positions of the A, B and C blocks, and that there are two of
them per joint.|
A plan view of the dome support shows it to be an
The first block. Use an A block to connect the shortest rectangular
panel with the shortest angled panel.|
Next add the second
block to this joint.
Then add the matching shortest angled
panel to the other side.
The progression. Moving left and right assemble the dome support
panels from the shortest towards the tallest panel. |
Unevenness in the floor might cause some minor alignment issues. If
this is the final location of the dome, then ensure that it is as
stable as it can be. Minor mismatches in the heights of the panels
is dealt with when screwing in the ledges.
Note the positions of the top joint blocks a
few inches below the rim.|
Clean the dome support area of all sawdust, screws, and any left over
pieces of wood.
Paint the inside of the dome support a flat matt black.
Matt black is used so that as little light as possible is reflected by
the dome support structure.
||A small extractor fan will be added to the dome
support at a later stage, to provide some airflow.|
Paint the outside of the dome any color you like.
Seal all the gaps on the outside. No light should get in through the joints between the
panels, nor around the sides of the door. Use a thick tape to seal the
joints. The door is more complicated, consider attaching a black felt
curtain on the inside to block out any light.
|Make sure to paint around all the
blocks, the door supports, and the top of the ledges. Also paint the
insides of the vent holes, and the edges of the doors. Try to paint to
the bottom of each panel without painting too much of the floor! Use
plastic tarps, or similar, to protect the flooring if necessary.|
To construct a dome support using 36 inch, rather than 48 inch, sides, use
the following table of measurements for the panel sizes. This will create a dome
support for a dome that is just over 9 feet in diameter. The dome support will
have a side to side diameter of 116.5 inches (about 9.5 feet) and a front to
back diameter of 104.1 inches. Obviously use 36 inch long ledge sections, but the blocks that fit
the dome support together have exactly the same angles as for the 48 inch sided
dome support. Note that the door for entry will now be quite short, so consider
adding 12 inches to the height of all the panels, if your location has the
|1||36 inch x 12 inch rectangle.|
|2||35 1/4 inch base, one side 12 inches, other side is 19 1/4
|2||34 inch base, one side is 19 1/4 inches, other side is 30
|2||34 inch base, one side is 30 15/16 inches, other side is 42
|2||35.26 inch base, one side is 42 11/16 inches, other side is 49
|1||36 inch x 49 7/8 inch rectangle.|
Click on the link below to run a utility program that will calculate the triangle and panel sizes required, given three inputs:
- The length of the sides of the equilateral triangles (triangle A).
- The height of the shortest panel in the dome support.
- The tilt angle in degrees. Though 20 degrees is recommended, other angles can be used, and the software can be configured to match.
Note that the utility requires scripts to be run, so if you get a security warning, be sure to Allow Blocked Content.
Note also that angles do not change with the size of the dome.
To construct the dome, go through the following procedure:
- Purchase the necessary materials:
Acquire the necessary tools:
- 40 sheets of corrugated cardboard, ideally with one side already white, 48 x
48 inches. Purchase an extra one or two if mistakes might be made. Alternatively
slightly fewer sheets are needed with 48 x 96 inch cardboard sheets (as three of
the smaller triangles can be cut per sheet) but there is a transport issue with
sheets of this size! So either buy 40 48 x 48 inch sheets, or 15 48 x 96 inch
sheets, plus a few extra as spares.
- 165 large (2 or more inch wide) paper binder clips. This provides three clips
- Black paper sheets totaling 48 inches long by 110 inches wide.
- Matt flat grey (not white) paint.
Very carefully draw out and then cut out the template triangles. Two
sizes of triangle are necessary, labeled as A and B in the following
- Sharp knife.
- Long metal edged scale.
- Sharp point, string, and pencil.
- Paint brushes, cleaning materials, newspaper.
When each triangle is cut out label the outside (not the white side if
white-sided cardboard is used), with the letters A or B.
Mark the lines where the flaps need to be folded with a pencil, then use
a dull point like a ball-point pen to score the cardboard without cutting
it to much. Practice on some scraps to gain some expertise first. Score the
cardboard triangles accurately and fold the flaps out.
Double check you have the correct quantities: 10 of triangle A, 30 of
triangle B, not including the two template triangles (which should be stored
separately and not painted - in case you need to redo one or more
At this stage the inside of the triangles should be painted a flat matt
latex grey. If white cardboard is used this should not take more than one coat of paint.
Make sure that the painting is done in a ventilated area, and appropriate
breathing masks are used. Brown cardboard may take a second coat of paint.
Although the temptation is to use a pure white paint, this will reflect too
much of the projection. A flat, light grey should give the best results. It
is not necessary to paint the flaps completely, but paint over the edges of
the triangles and into the flap area to ensure good coverage.
Use the full width of the 48 inch sheets.
To draw the triangle
you can use a sharp point with a string 48 inches long, and draw two
arcs. Where the arcs intersect is the tip of the triangle. Alternatively
calculate the height of the triangle (41.57 inches) - measure this along
both edges of the cardboard, then draw a line from one side to the
other, and mark the center - 24 inches along the line.
After cutting out the template, 10 triangles
of type A are needed.
Note that the triangle
is 48 inches on all sides, and that the flaps are in addition to this.
This is possible on a sheet of cardboard only 48 inches wide by having
the tapered flaps shown at the corners.
After cutting out the template, 30 triangles of type B are needed. This
will require 30 48 x 48 inch sheets, or 10 48 x 96 inch sheets, as three
triangles can be cut from the larger sheet.
13/16ths is a good
approximation for .82 inch. The height of the triangle is 34.25 inches.
Note that the triangle is 48 inches on one
side, and 41.82 on the other two sides, and that the flaps are in
addition to this.
After the cardboard is painted it may bow to varying degrees. When the
paint is dry consider stacking the triangles, perhaps with half facing the
opposite direction, with a weight carefully placed on top to help counteract
the bowing effect of the paint. In any case when the flaps are turned out
this will tend to flatten out the triangles again considerably, so the
bowing is not the serious issue that it might first look.
Optional step. Make black shades to block out light along the edges of
the pentagon. There are 55 sides internal to the dome, and 10 sides around the base.
The 55 internal edges are a mix of 48 and 41.8 inches. Cut out strips of
black paper long enough that two overlapping pieces will cover the whole
edge. Obviously shorter pieces can be used for the 41.8 inch sides. The
internal strips should be 2.25 inches wide (assuming cardboard that is one eighth of an inch wide), with a fold at 1 and 1.25 inches
along their full length. If the cardboard you have used is not one eighth of an inch wide, then the thickness of the square folds should simply be twice the
thickness of the cardboard. The folds need to be very straight for the shades
to fit neatly onto the edges. If a single fold is used the shades will tend
to keep the binder clips out from the join, which weakens the structure and
is prone to error. The reason why this step is optional is that to get
straight folded edges can require paper folding equipment that might not be
readily available. The images show a folding machine and the completed
shades. For the external 10 sides around the base, the paper strips should
be 3 inches wide, folded at 1 and 2 inches along the entire length of the
fun - though is usually done on a flat level surface!|
Time to get out those paper clips. Start with all the triangle Bs. These
are used to make the pentagons. Very carefully align the shorter edges of
the B triangles, place one or more of the black shades along each joint, and clip together a pentagon. Note that joining the last side
will lift the center of the pentagon about 9 inches. Ensure there is enough space around so
that these pentagons are not stepped on.
A paper folding machine is the best approach to getting very straight folds.
If such a folding machine is not available, try other long
straight edges such as a metal ruler.
First mark a sheet of black paper where it needs to be cut and folded. Then fold the sheet twice to create
the quarter inch square end. Then cut out the strip. Repeat until every
edge has two shades.
The image shows a quarter inch fold for
the triangles, and a one inch fold for the base.
A pentagon with shades attached.
With a lot of labor assistance (a minimum of five people works well), assemble the dome in the order shown in
the following diagram:
||The outside edges of the pentagon should all be the longer 48 inch
The 30 triangle Bs should be assembled into six pentagons.
Admire your work! The dome should now be reasonably rigid.
Ensure all the flaps of the lower edge are bent out, and carefully lift the dome
onto the support - with each of the 10 corners supported by an assistant
(hence the need for a minimum of five people). Do not lift the dome at any
time other that at its corners. Obviously the corners and 48 inch
edges of the dome should match the ledges of the dome support exactly.
Use the 20 heavy duty clips to attach the dome to the support, two clips per
Note that the central polygon is the very last piece to be assembled.
The dome will be quite floppy until this is done, and a lot of hands are
helpful at this stage.
When building the dome try to align the points and edges as
accurately as possible before proceeding to the next.
The critical stage in assembly is having enough hands inside the
dome to complete all but the top pentagon.
Because of the
difficulty in clipping in the top pentagon, consider having someone
stand on a stepping stool and held in place by a second person,
whilst the first leans over the dome and clips in the five last
sides. The people on the inside need to support both the last top
pentagon, and all the sides - at the same time.
Only when the last top pentagon is clipped into place does the dome
Open up a door and go inside!
height of the dome when it is on the floor and before it is tilted is just under 6.5
feet. After the 20 degree tilt the height is about 6 feet. Add to this
the height of the center of the dome support (just over 3 feet), and the
height of the planetarium is a few inches over 9 feet.
To construct a dome to fit the 36 inch side dome support, triangle A should
be an equilateral triangle with 36 inch sides. Triangle B should be an isosceles
triangle with a 36 inch base and two sides of 31 3/8 inches.
The height of a planetarium of this size is around 7 feet. The following images shows the relative sizes of the domes.
|48 inch triangle planetarium||36 inch triangle planetarium|
Adding ventilation to the planetarium will make the experience more pleasant for most people.
Electric power will be needed to power the external fan, and also obviously to power the internal projector.
- Purchase or acquire a small extractor fan (the fan must be capable of going into reverse - to extract the air - rather than just blow
- Using black foam-board, or a similar material, construct a box as shown in the image below.
- Power up the fan and check that the ventilation system works.
- Run a black power cable (25, 30 or even 50 feet) through one of the ventilation grill holes and up and over one of the doors so that the power outlets are available to the projector
that will be sitting on a shelf between the two doors. Consider using safety hooks
(cup hooks that close with a spring), or similar small hooks, to guide the power cable. Ensure that it
does not cross the floor at any stage inside the dome support, where it could be tripped on.,
and follows a safe path to the power outlet outside of the planetarium. If the
power cable or hooks are not black, then consider painting the hooks and
covering the cable inside the planetarium with black tape.
The cable in this image has
been left red to show its course. Covering the cable with black tape for
the inside section ensures minimal reflectivity.
Ideally the viewers inside the planetarium will be seated entirely below the base line of the dome - this is to ensure that no part of them blocks the
reflection from the mirror onto the dome surface. In practice this may be difficult to achieve, especially if height was an issue during construction. The
suggested layout is to lay black carpet tiles across most of the floor of the planetarium, with perhaps a few seats set at the back near the projector.
Shorter viewers sit at the front and middle of the planetarium, on the carpet,
taller viewers can use the seats at the back. The exact layout depends on the
number of viewers you plan to accommodate at any one time - all carpeting and no
seats, or all seats and no carpeting, are obviously options too.
The seats, similar to all items under the dome, should be as matt black as
High Quality Mirrors
- The mirror needs to be a half-dome spherical mirror as shown in the image below.
The cheapest of these are often made of plastic for use as safety mirrors in
parking garages for example, and if so are not very expensive, but do refer to
the note on High Quality Mirrors.
Experimenting with different sizes of spherical mirror.
The smaller, approximately 9 inch radius, worked well in our tests.
- The projector should provide as high a definition as possible. Ideally the
projector should be capable of full HD, 1920 x 1080p HD for example (which gives
a 16 x 9 aspect ratio). Such a projector will require a DVI or HDMI cable
to connect to the laptop. DVI is recommended as there is no use for the
audio connection in the HDMI cable. Alternatively a VGA projector could be used,
obviously with a VGA cable for the laptop connection.
A DVI cable.
- The mirror should be placed in the direct center on the highest side of the dome support, angled downwards at an angle of 20 degrees, and its base
should be at the same height at the base of the dome. The support for the mirror can be made out of wood, cut to give a 20 degree angle, or other options
can be used to provide some fine adjustment should it be necessary or helpful. In the image below a second tier keyboard support (for a music keyboard)
has been cut and drilled to provide a mirror support that can both take a variable size of mirror, and have the angle of the mirror finely adjusted.
- The projector needs to be placed pointing up at the mirror so that the image
is reflected off the mirror to fill the dome, but not the dome support. For this
a solid support system is needed that will safely hold the projector at an angle
of about 20 degrees, and provide fine turning adjustment. One good solution to this
is to use a solid music or conductors stand (as shown in the image below). These
can be found reasonably cheaply (around $50) and are surprisingly sturdy. Find
one that enables adjustment in both side to side, and up and down directions,
and is variable in height from around 24 to 40 inches.
It should also have lockable wheels - if it has wheels - in order
for its position to be reasonably secure after alignment.
Even though a music stand is designed to hold just paper,
a sturdy one can easily support and hold a projector at an angle.
- An alternative to the primary projection described in step 4, is to use a secondary mirror. Use of a secondary mirror has the advantage that the
projector and support are no longer near the center of the dome using up valuable spectator space. However the downside to using a secondary mirror is
that it involves additional cost (of the secondary mirror itself, and some
shelving), and complicates the alignment - the projector, secondary mirror, and spherical
mirror now all have to be aligned simultaneously and correctly.
To use the secondary mirror method of projection, first install a
shelving system that enables a variation in the height of the projector.
The shelf itself should be about 24 inches wide and 13 inches deep -
though this does obviously depend on the size of the projector you
intend to use.
Place the projector on the shelf so that the lens is centered -
which is why the shelf should be 24 inches wide, and not simply the
width of a projector.
The secondary mirror should be aligned
the top of the music stand. Heavy duty Velcro (or
similar) can be used to attach the mirror.
The fine alignment of the three main elements
(projector, secondary mirror, spherical mirror) will involve some
minor adjustments to the angles of each to get a complete image
projected onto the dome.
Note how close the secondary mirror
is to the projector. Just enough room is needed so that the
reflected image clears the projector itself and finds the spherical
This system frees up the center of the dome quite
Most mirrors reflect light from two surfaces, the inside and outside faces of
the glass or plastic. Unfortunately this means that there will be two images in
view on the dome for each single object in the simulated sky - the intended
image and a second fainter image slightly offset from the first. This problem is doubled if a secondary mirror also with two reflective surfaces is used - in this case there will now be four images on the dome, the intended one and three fainter ghost images. This problem can be eliminated with the use
of high quality first surface mirrors. These mirrors, both flat and spherical, have only one reflective surface, so even when a secondary mirror is used no unwanted ghost images
appear on the dome. Of course the issue here is cost, first surface mirrors are a few times more expensive than normal mirrors.
The use of first surface mirrors is recommended if your
- Connect a laptop computer to the projector, and if possible to the internet.
Without an internet connection you will be restricted to showing the tours and
collections files that are stored locally on the laptop, so in this case run all
the tours you might need once (which stores them locally) whilst connected to
the internet, before removing the connection and moving to the dome.
- Run the WorldWide Telescope Windows Client on the laptop. The Web Client
(based on Silverlight) does not currently support the dome warping software,
so make sure you are using the downloaded Windows Client version, and that
the version number (which can be verified in the About WorldWide
Telescope dialog) is 184.108.40.206 or later. It is recommended that you
use a Windows based laptop (Windows XP/Vista/7) for simplicity, but you can
use a Mac laptop with a Windows partition.
- Select Full Dome from the View menu,
then select Dome Setup to bring up the following dialog:
For most modern projectors the aspect ratio is 16:9, so set the Dome
Type to Mirrordome 16:9. If you are using an older VGA projector,
then the aspect ratio may well be 4:3, so set this value to Mirrordome 4:3. Refer to the Configuration section of the
WorldWide Telescope User Guide for details if your projector is neither of these.|
Set Dome Tilt to 70 percent. This value
contains the center of interest in vertical degrees.
high resolution projectors (1920 x 1080 or similar) select
Large Textures, otherwise leave this unselected.
- In the Full Dome menu ensure Full Dome has a tick beside it.
- If you wish to control the presentation by looking at the laptop, then you are good to go
- the mouse movements and clicks on the laptop screen control the view. If you wish to control the presentation by looking at the
dome projection, then select Detach Main View to Second Monitor. Consider using an XBox controller in this latter case,
as input control has now be passed to the dome view and controlling the
presentation with a mouse can be awkward.
- Invite your students and peers!