What is a nebula? How to instantly know what the new Webb Telescope images show

By Ronna M. Reed On Jul 24, 2022

The South Ring Nebula, captured by the James Webb Space Telescope (JWST).

NASA, ESA, CSA and STScI

It’s one of the most common words used by astronomers – and two of them appear in the first packet of images from the James Webb Space Telescope – but do you know what a nebula is?

If you think you do, you probably don’t.

This is because the word nebula actually has several different meanings. Boring, right? A symptom of “blurry spots” in the night sky being gradually revealed by better and better telescopes, the history of astronomy has left us with several completely different types of nebulae.

Here’s everything you need to know about this most beautiful word and the often weird and wonderful objects it refers to:

Why there are several types of nebula

A nebula – which comes from the Latin word for cloud – historically refers to something in the night sky that is neither a planet nor a comet. In short, a fuzzy spot in telescopes until the 20th century.

Many of those blurry spots turned out to be something else. For example, the Andromeda Nebula became the Andromeda Galaxy. However, the term nebula always refers to a cloud, especially of interstellar dust and gas.

One of the largest images ever taken by NASA’s Hubble Space Telescope of the Crab Nebula, shows … [+] Remains expanding six light years from a supernova explosion of a star, released December 2, 2005. Japanese and Chinese astronomers witnessed this violent event nearly 1,000 years ago in 1054, with, perhaps, Native Americans. The orange filaments are the remnants of the star and consist mostly of hydrogen. The rapidly rotating neutron star embedded in the center of the nebula is the dynamo that powers the strange bluish glow from within the nebula. The blue light comes from electrons whirling at near light speed around the neutron star’s magnetic field lines. The neutron star, the crushed ultra-dense core of the exploded star, ejects twin beams of radiation that appear to pulse 30 times per second due to the neutron star’s rotation. (Photo by NASA via Getty Images)

NASA via Getty Images

1. Planetary Nebula

The remnants of a supernova star are called a planetary nebula. Why? Their blue-green appearance is reminiscent of Uranus and Neptune. In a planetary nebula, the remnant core of a collapsed giant star – now a white dwarf – is producing enough energy to make its surrounding shell of gas glow.

Famous examples of a planetary nebula include:

This photo taken on September 25, 2019 shows the Orion Nebula, also known as Messier 42, M42 or … [+] NGC 1976, in the Milky Way.

Barcroft Media via Getty Images

2. Diffuse Nebula

Diffuse nebulae are a stage in the circle of life in the Universe. They are areas of cosmic gas and dust that give birth to stars. These star forming regions are among the most exciting objects to observe in the night sky and are often the targets of space telescopes. Since they emit their own light, these clouds of dust and gas are often also called emission nebulae.

Famous examples of a diffuse nebula include:

M45, the Pleiades star cluster, in a series of exposures to test image stacking with HDR … [+] techniques. I photographed the group in a series of 1, 2, 4 and 8 minute exposures, four from each exposure, all using the Nikon D750 and TMB 92mm refractor. A set of 1, 2, 4 and 8 minute exposures were stacked in Camera Raw using its HDR mode to create a new merged DNG file. I did this for four sets of 1-8 minute exposures, then processed each of the HDR stacks with shadows and highlights in ACR to bring out faint detail while retaining detail in the bright core . Each of the 4 HDR stacks was then combined in Photoshop and processed with Curves, S&H, B&C, etc. So in total. (Photo by: Alan Dyer/VW PICS/Universal Images Group via Getty Images)

Universal Images Group via Getty Images

3. Reflection Nebula

Clouds of dust and gas illuminated by nearby stars are called a reflection nebula. This scattering of light is sometimes called “cloudiness” and is best seen in the open Pleiades star cluster, which is easily visible to the naked eye from September to March.

Famous examples of reflection nebulae include:

The Pleiades (M45) in the constellation Taurus.
Witch Head Nebula (IC 2118) in the constellation Orion.
Ghost Nebula (IC 63) in the constellation Cassiopeia.

The Horsehead Nebula, Barnard 33 in the constellation Orion.

Getty

4. Dark Nebula

They are dark, dense clouds of interstellar dust that completely block visible wavelengths of light from objects behind them, including stars. The spaces between stars can tell us a lot about the night sky like the stars themselves, and many cultures have developed constellations based around these dark spots.

Famous examples of a dark nebula include:

Coalbag Nebula (TGU H1867) in the constellation Crux.
North American Nebula (NGC 7000) in the constellation Cygnus.
Horsehead Nebula (Barnard 33) in the constellation Orion.

I wish you clear skies and big eyes.