Comet C/2023 A3 near the mill The 1100 Roe

by Jeroen de Jongh Photography

Windmill De 1100 Roe is a historic windmill in Amsterdam, the Netherlands. The windmill was built in 1674. The 1100 Roe is a ground-sailer, a type of windmill whose sails come down to the ground. This makes it possible to operate the mill from the ground.

The name "1100 Roe" refers to the distance between the mill and Amsterdam's city limits, measured in rods, an old measure of length. One rod is about 3.76 metres, meaning the mill is about 4 kilometres away from the city. The mill was originally built to grind the Osdorper Binnenpolder dry.

Comet C/2023 A3 was independently discovered on 9 January 2023 by two teams: the Tsuchinshan observatory group in China and the ATLAS project (Asteroid Terrestrial-impact Last Alert System) in Hawaii. It is a long-period comet, meaning it will take a very long time to return to the inner solar system.

The comet will reach its closest point to the sun around 28 September 2024. At that time, the comet will be about 0.39 AU (astronomical units) away from the sun, which is less than Earth's distance from the sun. Like other comets, C/2023 A3 probably consists of ice, dust and rock. Comets are relics from the early history of the solar system, and their activity (e.g. developing a tail as they approach the sun) is caused by the sublimation of ice due to solar heat.