Capture a shadow cast by the planet Venus

An indoor astronomy project with a huge payoff: capturing a shadow cast by the light of the brilliant planet Venus.

A view out of the window with the shadow-casting Venus symbol attached to the glass. Venus’s light had to pass through tree branches on the way. Credit: Pete Lawrence
Published: March 26, 2020 at 11:00 am
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Venus’s brilliance comes about because it is a planet covered in reflective clouds which is close to the Sun and Earth. A good challenge is to see whether you can capture something that has rarely been photographed or seen visually: a shadow cast by Venus’s light.

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Although Venus is quite brilliant, its delicate shadow is easily lost due to extraneous lighting. Creating a dark environment to isolate the shadow is quite hard and requires thought.

Try and pick a night when the sky is clear and the Moon is not about. You’ll also need a relatively flat west to northwest horizon.

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For this to work you’ll need to be able to see Venus against an astronomically dark sky. This will occcur around 22:00 BST (21:00 UT) at the start of April 2020 and 23:15 BST (22:15 UT) at the month’s end.

A room with a west-facing window is ideal, but if one is not available, the next best thing is a cardboard box with one open end.

A shadow viewing screen can be made out of sheets of white paper fixed to a wall or used for lining the inside of a box. The shadow casting target is your choice; a cut out of the word ‘Venus’ or perhaps its planetary symbol + .

If you’re using the box option, ensure the target is rigidly fixed so it can’t move in a breeze.

As Venus is essentially a point source, the resulting shadows all appear sharp when cast on the wall. (Camera settings: ISO 12,800, 20” exposure at f/5.6). Credit: Pete Lawrence
As Venus is essentially a point source, the resulting shadows all appear sharp when cast on the wall. (Camera settings: ISO 12,800, 20” exposure at f/5.6). Credit: Pete Lawrence

Next, unless you’re in a really dark environment with crystal-clear skies, a camera will be required to record the shadow. A DSLR or MILC camera is ideal.

Set to a high ISO, a low f/number and use a remote shutter release to avoid camera shake. A tripod allows you to point the camera easily.

Illuminate the screen before your attempt, manually focusing on it as accurately as you can.

Do a test exposure of a few seconds up to tens of seconds. You may need to stretch the image using a photo editor
– open levels and adjust the sliders to just encompass the histogram peak – to reveal the shadow.

A useful technique is to make a time-lapse. As Venus sets, this reveals the shadow slowly creeping up the screen.

The non-shadowed area may change colour as the atmosphere makes the planet’s light slightly redder as it approaches the northwest horizon.

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Pete Lawrence is an experienced astronomer and a co-presenter of The Sky at Night. This article originally appeared in the April 2020 issue of BBC Sky at Night Magazine.

Authors

Pete Lawrence, astronomer and BBC The Sky at Night presenter.
Pete LawrenceAstronomer and presenter

Pete Lawrence is an experienced astronomer and astrophotographer, and a presenter on BBC's The Sky at Night.

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