On this day in 1999 – December 10th – the European Space Agency (ESA) launched the Newton X-Ray Multi-Mirror Telescope (XMM-Newton).
XMM-Newton, named after Sir Isaac Newton, was tasked with investigating interstellar X-ray sources, performing narrow- and broad-range spectroscopy, and performing the first simultaneous imaging of objects in both X-ray and optical (visible and ultraviolet) wavelengths.
On this day in 1546 – December 14th – Tycho Brahe was born.
The Danish astronomer was the greatest ever observer in the days before the telescope. His extensive collection of accurate observations made it possible for Kepler to work out the orbits of the planets.