Philipp Otto Runge’s Farbenkugel (1810). The top two images show the surface of the sphere, while the bottom two show horizontal and vertical cross sections.
From our selection of colour charts, wheels and tables through the centuries: https://t.co/lPctmDI0H6
The sun through a UV lens
This image is a combination of three different wavelengths of UV (171, 193, and 211 Angstroms), taken by the AIA telescope on NASA's Solar Dynamics Observatory (SDO).