The Merope Nebula (aka NGC 1435) is a diffuse reflection nebula in the Pleiades star cluster, surrounding the 4th magnitude star Merope. It appears to be about the size of the full moon. It is illuminated entirely by the star Merope which is embedded in the nebula. The nebula appears blue in visible light photographs because of the fine carbon dust spread throughout the cloud. The false color image above was put together using infrared data from the Spitzer Space Telescope. The visible light image below was taken by an amateur astronomer.
Image Credits: NASA / Karol Masztalerz (CC BY-SA 4.0)