Experiments with Venus

Try out these activities while the Evening Star is shining bright in our skies

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Venus is well-placed in the evening twilight this month, an intense blaze of light, difficult to miss in clear skies. It's an interesting object astronomically, showing subtle atmospheric markings through the eyepiece, as well as displaying striking changes in phase and apparent diameter.

It's interesting for another reason too. Being so intensely bright - the brightest of all the planets - it's essentially a point source at low magnification, and ideal for demonstrating experiments with light. When placed in a dark sky, it's possible to experience its light casting a shadow- okay, it's a dim shadow, but it's one that can be photographed. Being very close to a point light source, the shadow cast is really sharp and well-defined too.

To record this elusive effect, you'll need to be somewhere where there are no other light sources. Even a bright sky can interfere. A west or northwest-facing window is ideal, as long as you can turn all of the lights off. If you can't do this, use a large cardboard box with the opening pointed at Venus. Either way, you'll need a screen on which the shadow will be cast. This can be as simple as a light-coloured wall or several large white sheets of paper.

You'll need a shadow-casting subject as well. This can be a shape cut from card pasted on a window or suspended in front of the box. Then it's simply a case of pointing a camera at the screen, focusing and taking your shot. A high ISO is recommended to keep the exposure times short; take too long and the razor-sharp edge of the shadow will blur as Venus moves relative to the horizon.

Make a rainbow