Build Your Own Venusian Transit Machine

Previously (“Transit of Venus”) to honour Captain James Cook’s epic effort in 1769 to observe the transit of Venus from Tahiti I mentioned that I’m going to attempt to observe the last transit of Venus this century; well, I’m probably going to have lost my eyesight (or worse) by the next chance in 2117. I have been playing around with various options and have settled on a camera obscura design, the prototype of which has worked surprisingly well. Here’s how to make one, so you can be ready for the big moment on 6th June 6am (AWST)/8am (AEST) when Venus passes in front of the sun.

You will need:

1. A north or east facing area to observe the rising sun. I’m using a balcony but you’re free to use a patio, or perhaps even a small clearing in a forest. The view of the sunrise is the key thing.

2. A box containing 24 bottles of Monteith’s Summer Ale

3. A small hand mirror

4. A sharp pencil

5. A dressing mirror

6. A comfortable chair

7. An accurate timepiece

8. A copy of Kernighan & Ritchie’s landmark C programming language 2nd edition

9. A fresh lime

First, carefully open the box of summer ale and set the content aside in a cool place for later. Next, take the sharp pencil and poke a hole in the centre of the base of the box no more than 3mm thick. Position the box so that the base is directly facing the sun. This should result in a thin beam of sunlight shining through the hole you just created.

Quickly, take a sharp knife and slice open and drink the juice of the lime. This is important, since it will reduce significantly the possibility of suffering from scurvy during the observation, a detail Cook was only too aware of. Take the hand mirror and prop it up on Kernighan and Richie’s excellent tome at an angle such that the beam is directed onto the large dressing mirror. Finally align the large mirror so that the beam travels onto a wall in a shaded area, such as a darkened bedroom. The key thing here is to use the mirrors to lengthen the journey to the viewing wall as much as possible, which will give the pinprick of light more time to broaden out into a larger image. From experiment, a 3mm wide beam travelling for 30m yields a sun image roughly 25cm across, which should be ample to observe the disc of Venus.

Finally, and optionally, recline in the comfortable chair and open a refreshing ale to celebrate viewing one of nature’s rarer spectacles. Good luck!