The celestial sphere

celestial sphere Introduction Looking up at the night sky, you might get the impression that the stars are all at the same distance from you as if they were on the surface of a sphere. This imaginary sphere is called the celestial sphere. Although we know that the...

Theory problems and solutions from Thailand 2007

IOAA problems Introduction The very first IOAA took place in Chiang Mai, Thailand in 2007. 21 countries competed. You can find the archived website of the competition here. If you find these problems too hard, you might want to start with some of our easier problems,...