What is a Nebula?
What is a Nebula?
A Nebula is named from the Greek word for “cloud”. Nebulae (plural) come in many shapes and sizes and have a way of captivating those that observe and photograph these deep sky objects in space.
“a nebula is a cloud of gas and dust in outer space, visible in the night sky either as an indistinct bright patch or as a dark silhouette against other luminous matter.”
A nebula is a giant, interstellar cloud of gas and dust in space, formed from stars. Nebulae have varying compositions depending how they were formed and where they are.
Examples of nebulae I have photographed from my backyard.
Nebulae usually consist of Hydrogen and Helium, as these are the most common and stable compounds in the Universe. The formation of a nebula can occur when a star undergoes a significant change, such as excess fusion in its core.
In the case of a planetary nebula, the formation of this deep sky object occurs when a white dwarf star explodes explodes during a supernova. The explosion sends interstellar materials into space that can eventually form into a nebula.
The Four Main Types of Nebulae
Emission Nebula / Star-Forming Region
As gravity continues to merge these materials together, the region becomes hot enough to create a new star. The remaining materials may form into Planets that will orbit the star, just as our Solar System was formed.
The Orion Nebula is an emission nebula and star-forming region. It is the most active star-forming region in our Galaxy, and can easily be observed up-close with a small telescope.
The Orion Nebula is a perfect example of a star-forming region or “stellar nursery”.
When early astronomers observed these round, compact nebulae in the night sky – they thought that they must be planets. In reality, planetary nebulae have nothing to do with a planet.
Planetary nebulae are formed when a star dies, and create dramatic formations of radiating cosmic gas. Some great examples of planetary nebulae in the night sky include the Ring Nebula, the Dumbbell Nebula, and the Helix Nebula.
The Dumbbell Nebula photographed using a camera and telescope.
The gas is expanding outwards at an incredible speed, and this movement has been documented in the following timelapse of V838 Monocerotis captured over time by Hubble.
A supernova remnant is a cosmic explosion that has spread the materials from a star across a huge expanse of space. The remnants of this explosion have formed into a nebula, and this nebula type creates some of the most incredible formations in space.
The Veil Nebula is a prime example of Supernova Remnant, as seen as this image captured using a small telescope in my backyard. The Veil Nebula includes several filimentary nebulae, including Pickering’s Triangle.
The Eastern Veil Nebula is a Supernova Remnant.
A Dark Nebula is a cloud of gas and dust that is revealed due to the bright areas of interstellar material and stars behind it. The nebula is silhouetted against a bright background to create interesting shapes and formations.
Examples of dark nebulae include the Coalsack Nebula, and the Horsehead Nebula. This nebula is composed of thick clouds of dust that block the bright emission nebula gas behind it.
The Horsehead Nebula is perhaps the most iconic Dark Nebula in the night sky.
Some deep sky objects combine different types of nebulae in one. A prime example of this type of object is the Trifid Nebula.
The Trifid Nebula consists of an emission nebula, reflection nebula, and a dark nebula in one. It is the perfect example of a combination nebula with a complex and unique structure.
The Trifid Nebula combines an emission nebula, reflection nebula, and dark nebula into one.
All Nebula Types
- Emission Nebula
- Example: Omega Nebula
- Reflection Nebula
- Example: Iris Nebula
- Dark Nebula
- Example: Horsehead Nebula
- Planetary Nebula
- Example: Dumbbell Nebula
- Supernova Remnant
- Example: Veil Nebula
What Causes a Nebula?
Essentially, a nebula is formed when portions of the interstellar material experience a gravitational collapse. Mutual gravitational attraction causes matter in space to gather and join together, forming areas of intensifying density.
Stars may begin to form in the central region of this collapsing material. The ultraviolet ionizing radiation causes the gas surrounding the star to become visible in optical wavelengths (what our eyes can see). These formations can be hundreds of light years in diameter.
Thor’s Helmet Nebula in Canis Major (Emission Nebula).
When it comes to photographing deep sky objects using a camera and telescope, there are three main types of targets to photograph. These are Nebulae, Galaxies, and Star Clusters. Nebulae are my favorite type of deep sky object to photograph due to their large size and varying color combinations and compositions.
Some nebulae have extremely large apparent dimensions, as is the case with the North America Nebula. This massive nebula (120 x 100 arcmins) was named after the shape of the continent it resembles. The photo below shows the location of this giant nebula in the constellation Cygnus.
You can view the images of nebulae I have photographed with my camera and telescope in my astrophotography image gallery. To learn how to take pictures of objects in space, please see my complete beginners guide.