An image of three continuously bouncing oil droplets was the winner of this year's competition.
A clown fish floats among the tentacles of a bleaching sea anemone in Thuwal, Saudia Arabia. Morgan Bennett-Smith
Most tornadoes start as funnel clouds, such as this large one in the Yukon, Canada. Lauren Marchant
Blue-spotted mudskippers skirmish in the Mai Po wetlands, Hong Kong. Daniel Field
A lunar halo above the forest of Mogilev, Belarus demonstrates a phenomenon often seen in frosty weather when there is high humidity. Mikhail Kapychka
A white coating is spread by the rotting stems of water lilies in the Ľuboreč water reservoir, Slovakia. Daniela Rapava
Ferrofluids shapeshift under the magnetic field created by two rare-earth disc magnets. Aleks Labuda
A young blue trevally feeds on a purple jellyfish, and guards it against others who may wish to do the same.
Mammatus clouds -- formed when downward currents collide with rising warm air -- seen after a sunset in Wyoming, USA. Cándido R. Vicente Calle
In August 2018, Anak Krakatau in East Asia, is seen here at the start of its eruptive phase. Later, its southwestern flank collapsed and caused a tsunami, which killed hundreds of people in December 2018. James Moore