A rare total solar eclipse is set to sweep across Europe and the Arctic, with parts of northern Spain briefly turning from day to night as the Moon blocks out the Sun. Millions of people in Spain will have some of mainland Europe's best views of the celestial spectacle, which will begin around sunset when the sun, moon and Earth align. Millions more across Europe, Canada, the northern US and northwest Africa will see a partial eclipse. Beyond the spectacle, scientists say eclipses offer valuable insights into the Sun and our universe. Meanwhile, Spain is also facing concern over heat and wildfires as the event approaches.