BBC Sky at Night Magazine

DIY Astronomy

Create an indoor view of the night sky by projecting the magazine’s all-sky chart

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This month we’ve got a family friendly project that you can build with minimal tools and basic skills. It’s a planetariu­m projector that projects a view of the night sky onto a bedroom ceiling. It uses a normal LED torch as a light source and the pull-out all-sky chart from our monthly ‘Sky Guide’ (on page 46) to position the pinholes you make for the stars. As well as being fun to make it’s educationa­l, as you can use it to learn how to navigate between the constellat­ions. And by making multiple pinhole ‘slides’ you can demonstrat­e how the sky changes through the seasons.

Filling your room with stars

To use the projector, find a clear space on the floor for the torch in its base. Next, place the box over the torch, lay a night-sky slide on the top and switch on. You could orientate the projector so that the compass points (north, east, south and west) correspond with the edges of the ceiling. It is important to use a torch with a single, small light source (an LED or tiny bulb) and it should also produce a fairly wide beam. Our torch had a ‘Zoom’ feature and we used it on the widest setting. Before starting the project, you need to hold your torch above the chart so that its circular beam of light just spills beyond the chart’s edge, and measure the distance (h) between the torch and chart. You’ll need this dimension (h) for the downloadab­le diagram (see page 5 for details) to mark out your box sides.

The box and slide frames are made from some stiff cardboard. After cutting out, we used a hot-melt glue gun to join the sides, but strong tape would be fine. The inside must not create reflection­s, so we combined sawdust and matt black paint to overcome this. It is easier to paint the insides before gluing the top section on.

The stand will need to suit your torch, but a fairly heavy base with a hole that the torch can be stood in is a simple solution. Two walls made from offcuts of wood hold the box above the torch, so that the top of the torch just reaches the fold line of the box, close to the distance (h) from the slide at the top.

Next, paint the underside of some foil matt black and mount it to a cardboard slide with a glue stick, and you are ready to start making the holes for the stars. You need to work on the foil’s underside or you will find your east and west are reversed when you project the stars: so place the sky chart over the black side of the foil and begin making the pin holes. You need the tiniest holes you can possibly make; we estimate that the resulting stars are about 10 to 20 times the size of the holes you make, so small is beautiful.

You may not want to pick out all the stars on the chart; you might, for example, decide to just include the main constellat­ion stars. If you are very careful you can vary the hole sizes to emphasise bright stars or pick out planets for added effect.

 ??  ?? ▶ Star maker: the completed planetariu­m projector uses the monthly all-sky chart to create an illuminate­d star field
▶ Star maker: the completed planetariu­m projector uses the monthly all-sky chart to create an illuminate­d star field
 ??  ?? Mark Parrish is a bespoke designer. See more of his work at: buttondesi­gn.co.uk
Mark Parrish is a bespoke designer. See more of his work at: buttondesi­gn.co.uk
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