India's first satellite, Aryabhata, built by the Indian Space Research Organisation, was launched on April 19, 1975, by the Soviet Union. Weighing 360 kg and built to conduct experiments in X-ray astronomy, aeronomics, and solar physics, Aryabhata re-entered the Earth's atmosphere in 1992. The satellite was named after an Indian mathematician-astronomer who is believed to have discovered 'zero'.