The competition, which is run by the Royal Observatory Greenwich in association with BBC Sky at Night Magazine, is now in its sixth year and has received over 2,500 entries. Photo: Centre of the Heart Nebula by Ivan Eder (Hungary). Situated 7500 light years away in the “W”-shaped constellation of Cassiopeia, the Heart Nebula is a vast region of glowing gas, energized by a cluster of young stars at its centre. The image depicts the central region, where dust clouds are being eroded and moulded into rugged shapes by the searing cosmic radiation. (Photo by Ivan Eder)

An Israeli army officer gives explanations to journalists during an army organised tour in a tunnel said to be used by Palestinian militants for cross-border attacks, July 25, 2014. (Photo by Jack Guez/Reuters)

The Northern Lights glow green in a spectacular light show above a field of trees frozen solid with snow. (Photo by Jaak Sarv/Solent News & Photo Agency)

A man wearing a mask and dressed in a clown costume rides an electric tricycle while carrying a container in the shape of a rubber duck amid heavy smog in Beijing, China, December 29, 2015. (Photo by Jason Lee/Reuters)

A brilliant sunset makes for a fun silhouette picture by jumping between sand bars at Shi Shi Beach on the Olympic Peninsula Friday July 17, 2015. (Photo by Bettina Hansen/The Seattle Times)

Luling, Louisiana, US. New evidence contradicts previous claims of the relative safety of glyphosate, the world’s most widely used herbicide, which is manufactured here. It is often used in conjunction with seeds that have been genetically modified to tolerate its application, meaning that anyone consuming these crops is eating a genetically modified plant, and whatever residue of the pesticide that remains. (Photo by J. Henry Fair/Industrial Scars/Papadakis Publisher)

A remote-controlled plane in the form of a witch flies over a neighborhood as the sun sets during Halloween in Encinitas, California, U.S. October 31, 2016. (Photo by Mike Blake/Reuters)

A boy and a serviceman pose for a picture during Marines Day celebration in the Black Sea port of Sevastopol, Crimea, November 27, 2016. (Photo by Pavel Rebrov/Reuters)