In 1681 Flamsteed proposed that the two great comets observed in November and December 1680 were not separate bodies, but rather a single comet travelling first towards the Sun and then away from it. Although Isaac Newton first disagreed with Flamsteed, he later came to agree with him and theorized that comets, like planets, moved around the Sun in large, closed elliptical orbits. Flamsteed later learned that Newton had gained access to his observations and data through Edmund Halley, his former assistant with whom he previously had a cordial relationship.