Today there is just grass and shrubs to reflect the midday sun towards the back of the thermometer box.

As Craig Kelly said: "The fact that it's disappeared shows that it was never installed – someone at the BOM just happened to grab a random solar panel and place it at such an unexplained position…"

So much for expert rigorous science accurate to a tenth of a degree.

Kelly explains that this site is nearly invisible:  "The only way you can see it is by holding a camera above your head – it's not visible to the eye – even if you were 6'6" and standing on your toes you can't see over the fence – and the Observatory is closed to the public for some unknown reason."

Perhaps the BOM just thought no one would notice, and "it's for a good cause, eh?" We can't have the punters thinking Sydney was cooler today than in 1883.

As I said:

The solar panel was exactly due south of the Stevenson screen on exactly the right day. If, hypothetically, someone wanted to leave a reflective object pointed at the box at midday, that'd be the place to do it.

Look for the handy BOM guidebook:

"How to create temperature records with spare parts lying around the house"