M27 Dumbell Nebula is a planetary nebula. The red light is produced by the emission spectrum of hydrogen (H alpha). The bluish green light is produced by the emission spectrum of doubly ionized oxygen (O III). The O III spectrum has a very low probability of energy level transition, making it very difficult to replicate in a laboratory on Earth but can be found in diffuse and planetary nebulae. This image was obtained using a broadband filter. Exposure time was set at 20 min to achieve what would have required dozens of hours of accumulated exposure using a small telescope.
2019.07.13 - 2020.02.16