Tonight at 11:27pm, South African time, you need to step outside and look upwards. Bring a camera. As an Urban Astronomer reader, you already know that the Cassini robotic spacecraft will pause in its mission to study Saturn and it's moons to look back home and take a photograph of Earth. The camera's shutter will be held open for 15 minutes (at a billion kilometers distance, Earth is a surprisingly dim dot) so you've got that long to take part in the Day The Earth Smiled festivities by joining the rest of humanity in the largest ever photo-bomb. Go outside, wave, tell people what's going on and get them to wave too. And take pictures of yourself doing this to commemorate the event. TWAN (The World At Night - "a program to create and exhibit a collection of stunning landscape astrophotographs and time-lapse videos of the world’s most beautiful and historic sites against a nighttime backdrop of stars, planets and celestial events", according to their website) are encouraging as many people as possible to take photographs of people waving at Saturn, photographs of Saturn, and anything else related to the event. They plan to merge these images into a giant mosaic, to simulate what Cassini can actually see.
It's all a bit of silly fun, really, since the Earth will appear as only a single pixel in the resulting photograph which will only be ready for viewing after 6 months, but TWAN's effort will allow us to pretend that we can zoom in on that pixel and see ourselves waving back. And if it gets people to look up, notice the sky, and realise that they can easily see the five classical planets with just their own naked eyes, well then we'll have achieved something special.
Meanwhile, you're probably wondering where exactly to look? Luckily, Saturn is easy to find. For South Africans, it will be fairly low in the western sky at the critical time. Just face west, and look for the Moon. Saturn will be a bright beige-brown star almost directly beneath it. The Southern Cross, if you know how to recognise it, will be to the left. If you're not sure, use the planetarium image on the left (click to enlarge) as your guide. Now straighten your hair, get out there and smile!