The earth must have a huge cavity, this is the conclusion of one of the most famous scientists of his time in 1692: Edmond Halley, renowned astronomer and mathematician, explorer of the comet named after him. Halley compared the mass and density of earth and moon, using formulas by Isaac Newton. The one, however, had miscalculated. And so Halley is wrong. He assumes that the two celestial bodies are made of the same material, and concludes that the earth has no core, but must be hollow on the inside. He considers strong auroras, which caused a sensation in 1716, to shine from within the planet.