A small section of the expanding remains of the Veil Nebula, a massive star that exploded about 8,000 years ago. The entire nebula is 110 light-years across, covering six full moons on the sky as seen from Earth, and resides about 2,100 light-years away in the constellation Cygnus, the Swan. Image taken by NASA's Hubble Space Telescope. Released September 24, 2015. (Photo by Reuters/NASA/ESA/Hubble Heritage Team)

A woman walks on the stairs decorated with an image of two hands shaking to form the shape of the Korean Peninsula to support the upcoming inter- Korean summit, in downtown Seoul on September 17, 2018. South Korean President Moon Jae- in will fly to the North Korean capital on September 18, for his third summit with the North' s leader Kim Jong Un as a rapid diplomatic thaw takes hold on the peninsula despite stalled progress in denuclearisation talks between Pyongyang and Washington. (Photo by Jung Yeon-je/AFP Photo)

A boy holds a machine gun at a military hardware exhibition during a swear-in ceremony for new recruits of the Russian military-patriotic club “Yunarmia” (Young army) in the Black Sea port of Sevastopol, Crimea, October 27, 2018. (Photo by Pavel Rebrov/Reuters)

An army dog stands up as retiring soldiers salute their guard post before retirement in Suqian, Jiangsu province, China on November 29, 2017. (Photo by Reuters/China Stringer Network)

A general view of atmosphere at the annual VOLT Festival in Sopron, 208 kms west of Budapest, Hungary on June 26, 2017. (Photo by Mudra László/Rockstar Photographers)

Female labourers wearing helmets take a break from laying underground electricity cables in Ahmedabad, India, March 7, 2016. (Photo by Amit Dave/Reuters)

Tomomi Ota pushes a trolley loaded with her humanoid robot Pepper as she crosses a street in Omotesando shopping district in Tokyo, Japan, 24 March 2016. Telecommunications and mobile phone carrier SoftBank Corp. opened a robot-staffed store where 10 Pepper humanoid robots welcome customers looking to buy a mobile phone. The store will be opened until 30 March 2016. (Photo by Franck Robichon/EPA)

In this Tuesday, April 16, 2019, file photo, a visitor posing for a photo walks though azalea blossoms at Nezu Shrine during a day of mild spring weather in Tokyo. Nezu Shrine is one of the oldest shrines in Tokyo. (Photo by Eugene Hoshiko/AP Photo/File)