An extraordinary sight should be visible in the sky tonight as a giant comet passes in front of a star.
Comet Holmes has put on a spectacular display for amateur astronomers for the past three weeks. Tonight it is expected to shine even brighter as it passes in front of Mirfak, the brightest star in the constellation Perseus.
Comet Holmes appears in our skies every several years, usually as a very dim speck of light. But on October 24 astronomers were astonished to see it explode suddenly into a colossal light, a million times brighter than before, and clear enough to see as a fuzzy dot with the naked eye. Although the icy nucleus of the comet is only 1.9 miles (3km) across, the halo of light around swelled to a ball of 900,000 miles (1,45 million km) in diameter, the largest light in the solar system, bigger than the Sun, which is a mere 1.39 million km diameter.