Soap Bubble Structures by Kym Cox. Bubbles optimise space and minimise their surface area for a given volume of air. This phenomenon makes them a useful tool in many areas of research, in particular, materials science and “packing” – how things fit together. Bubble walls drain under gravity, thin at the top, thick at the bottom, which interferes with travelling lightwaves to create bands of colour. Black spots show the wall is too thin for interference colours, indicating the bubble is about to burst. (Photo by Kym Cox/2019 Science Photographer of the Year/RPS)

Jack, a Lurcher from Dogs Trust Salisbury, walks past a window display of models in a Dogs Trust shop window in Salisbury, as part of a campaign to discourage the impulse buying of dogs ahead of Valentine's Day, on February 10, 2014. (Photo by Matt Alexander/PA Wire)

Solid Light, an exhibition of the immersive works of Anthony McCall, opens at Tate Modern in London on June 25, 2024. Installations use beams of light projected through a thin mist to create large three-dimensional forms. (Photo by Guy Bell/Alamy Live News)

Three prostitutes lean out of a window in Santiago, Chile, in an attempt to entice customers inside, circa 1950. (Photo by Three Lions/Getty Images)

A Lion peers out of a window on Fitzwilliam Square, Dublin, Republic of Ireland on October 25, 2022. (Photo by Dara Mac Dónaill/The Irish Times)

People are reflected in a shop window as they walk along a street in a shopping district in Tokyo, Japan June 25, 2015. (Photo by Thomas Peter/Reuters)

A bank employee exits the bank through a window broken by attackers, in Beirut, Lebanon, Wednesday, September 14, 2022. (Photo by Hussein Malla/AP Photo)

Penitentes, or nieves penitentes (Spanish for “penitent-shaped snows”), are a snow formation found at high altitudes. They take the form of tall thin blades of hardened snow or ice, closely spaced with the blades oriented towards the general direction of the sun.