A year of sky
A year of sky This is what a year of skywatching yields. Throughout 2021, astronomer Cees Bassa used an all-sky camera to take an image of the sky over the Netherlands every fifteen minutes. Combined into what’s known as a keogram, the images show the daytime sky (mostly blue, with more white on cloudy days) and nighttime sky (mostly black, with more white on moonlit nights) progressing horizontally each day, stacked vertically to show the entire year. You can see the changes in the length of the days and nights throughout the year taking the shape of an hourglass. Cees Bassa/Netherlands Institute for Radio Astronomy