December 21 is the winter solstice, the longest night of the year in the Northern Hemisphere. This year though, the world will also witness a spectacular celestial event on this night. In this photo, the Moon, left, Saturn, upper right and Jupiter, lower right, are seen after sunset with the Washington Monument December 17, 2020, in Washington, DC. Both planets will be ’in conjunction’ with each other December 21. Photo: National Aeronautics and Space Administration That is the time when both will be separated by just one-tenth of a degree. This event is happening after 800 years. The last time it took place, it was the time of the High Middle Ages. Here, Saturn, top and Jupiter, bottom, are seen after sunset from Alexandria, Virginia, December 17, 2020. Photo: NASAWhile the two planets will appear to be close to each other, in reality, they will be 450 million miles (724 million kilometres) apart. Here, the Moon, left, Saturn, upper right and Jupiter, lower right, are seen after sunset from Washington, DC, December 17, 2020. Photo: NASAFor watching the event, just wait for an hour after sunset. Then, look onto the southwestern sky with either a binoculars or a simple telescope. Here, Saturn, top and Jupiter, below, are seen after sunset from Shenandoah National Park in Viginia, US, December 13, 2020. Photo: NASA