# Category Archives: Geography

# The Camera Obscura at the Royal Observatory in Greenwich

# We’ve found the real 0° meridian!

And it turned out to be a that little path next to the Royal Observatory in Greenwich, not the Prime Meridian line. The 0° meridian is what the GPS uses for global navigation, the discrepancy results from the fact that the Prime Meridian was originally measured without taking it into consideration that the Earth isn’t a perfect smooth ball (if the measurements are made inside the UK, as it it was originally done, this does’t lead to as much discrepancy as when vaster areas are included).

# Pathfinding algorithms: Dijkstra’s and Breadth-first search

The photos below show Simon playing with Breadth-first search and Dijkstra’s algorithms to find the most efficient path from S to E on a set of graphs. The two more complex graphs are weighed and undirected. To make it more fun, I suggest we pretend we travel from, say, Stockholm to Eindhoven and name all the intermediate stops as well, depending on their first letters. And the weights become ticket prices. Just to make it clear, it was I who needed to add this fun bit with the pretend play, Simon was perfectly happy with the abstract graphs (although he did enjoy my company doing this and my cranking up a joke every now and then regarding taking a detour to Eindhoven via South Africa).

# Dijkstra’s pathfinding algorithm

“I have first built a maze, then I turned it into a graph and applied Dijkstra’s pathfinding algorithm!”

Simon learned this from the Computerphile channel. He later also attempted to solve the same maze using another pathfinding algorithm (A-Star).

# Thin ice plates behaving like tectonic plates

And some more winter physics: trying to powders snow and ice:

# Newtonian GPS would place you on the wrong planet!

Simon explains why our modern satellite navigation (the Global Positioning System or GPS) is a great experimental proof for Einstein’s relativity theory and what would happen if the software calculated your car’s location using Newtonian dynamics.

Simon learned about this from Ian Stewart’s awesome book “17 Equations that Changed the World”, Chapter 13 (Relativity).

# The rest of the trip to London

Simon loved the Science Museum, even though he did not get to see the Klein Bottles from the museum’s permanent collection (none of them was on display). He particularly enjoyed the math and information age spaces. The Original Tour was a success, too – giggling at all the jokes on the English audio guide, he was bubbling with joy that he could follow everything and was actively studying the map, together with Dad. The only thing Simon really hated to tears was The Tower.

# The skyscraper that set things on fire

Inspired by Matt Parker’s video about the uniquely shaped building at 20 Fenchurch Street in London, Simon was very excited to visit this address. In the video below, made on the pavement in front of the skyscraper, Simon shows the geometric proof (he learned from Matt) of why the building’s shape used to let it set things on fire on extremely sunny days.

# Catenaries

Simon showing us catenaries made of soap, as he brings two plastic bands apart after dipping them in soapy water: