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

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.

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:

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:

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.

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.

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