Mandatory Credit: Photo by Peter Greig/Bav Media/Shutterstock (10712329c) Comet NEOWISE over Stonehenge, Wiltshire, in the early hours of Monday morning. Comet NEOWISE over Stonehenge, UK - 12 Jul 2020 The comet which was discovered on 27 March 2020 by the NEOWISE space telescope, will make its closest approach to Earth on July 23, passing the planet at a distance of 103 million km - about 400 times further away than the moon. Comets are 'cosmic snowballs of frozen gases, rock and dust that orbit the Sun', leftover from the formation of the solar system, according to NASA.Their size can range from a few miles wide to tens of miles wide - but as they orbit closer to the sun, they heat up and spew gases and dust into a glowing head that can be larger than a planet.As these substances stream off the comet, they form a spectacular gas and dust cloud that tails behind them for millions of miles - and can often be seen from earth with the naked eye.