Nebulae

Types of Nebulae

There are five different types of nebulae. The nebulae captured by most astrophotographers are all located within the Milky Way. The targets below are from the Messier Catalogue as well as Caldwell, New General, Sharpless, and Index Catalogues. I try to spend at least three hours on each nebula before I’ll consider it worthy to print, although it depends on the brightness and position in the sky. Some targets might need only 30-minutes while others will need 10 hours or more.

• Emission Nebulae are clouds of ionized gas that emit their own light. Most of these targets are made of hydrogen gas, making them easier to image using a Hydrogen Alpha (Ha) filter, which captures its signature red color. Another common wavelength emitted is Oxygen-III (OIII) and produces a teal color. Both wavelengths can be captured at the same time using a color camera and a dual-band filter.
• Planetary Nebulae are actually a sub-type of emission nebulae. The term “planetary” may be confusing because they don’t have anything to do with planets. The name was coined due to their brightness and shape through a telescope, similar to planets.
• The opposite of emission nebulae are Reflection Nebulae. Instead of emitting their own light, these are just gas clouds that reflect the light from nearby stars. These targets tend to lean toward the blue color spectrum, and can sometimes to located close to other emission nebulae.
• Dark Nebulae, or absorption nebulae, are interstellar gases that are thick enough that light cannot pass through or reflect off them. These targets are visible to us if their gases are in between us and a brighter nebula or star cluster.
• Supernova Remnants appear when a large star becomes a supernova. This creates shockwaves of ionized gas that expand outward at great speeds.