What is Nebula and how it works ?

We have something known as Dark nebulae. They are so called because the interstellar clouds are so dense that they block any light from background stars and/or reflection nebulae

Dark nebulae can be observed against the backdrop of light. Dark nebulae are capable of blocking light because the dust particles which are of the size of sub-micrometer have coats of frozen nitrogen and carbon monoxide that can block light at visible wavelengths.

Dark nebulae are invisible without the backdrop of light such as Milky Way, it never means that they are not important. They can give birth to planets, stars, moons etc. Great Rift and Coalsack Nebula are two examples of dark nebulae that are visible to naked eyes as they appear as darker patches against the bright background of our Milky Way.

About 5 billion years from now, our Sun will become a nebula

The nebula closest to Earth is the Orion nebula which is at a distance of 1,300 light years from us. The nebula stretches to a distance of 25 light years.

Until 1920s, scientists used to classify distant galaxies as nebulae

Some nebulae may have parts of other nebulae inside them. A typical example is the Gum nebula which contains the Vela nebula inside it.

Nebulae outside the Milky Way are referred to as extra-galactic nebulae.

Planetary nebulae have average temperature ranging between 8,000 Kelvins and 23,000 Kelvins (7726.85 degrees Celsius and 22726.85 degrees Celsius). However, closer to the surface of star, the temperature can be as high as 100,000 Kelvins or 99726.85 degrees Celsius.

It is estimated that there are at least 10,000 planetary nebulae in our Milky Way Galaxy. However, so far only 2,000 have been detected.

A planetary nebula has a life span of tens of thousands of years, which though very high is actually very insignificant compared to astronomical standards.

Planetary nebulae are primarily composed of carbon, neon, nitrogen, oxygen and other elements that have more or less the same weight as the predominant ones. Small amounts of metals and helium are also present in planetary nebulae.

Planetary nebulae expand at a rate of 20 km per second per second. This expansion rate can be as high at 30 km per second per second (km/s2).

Planetary nebulae expand at a rate of 20 km per second per second. This expansion rate can be as high at 30 km per second per second (km/s2).

The gas cloud of a planetary nebula has a density ranging between 103 to 106 particles per centimeter. This density decreases as the age of the nebula increases.

Nearly 90% to 95% of the light emitted by a planetary nebula is green, i.e. the light has a wavelength of 500.7 nm. This green color comes from the oxygen ions present in a particular state inside the nebula

Nebula M27 was the first planetary nebula that was discovered on July 12, 1764. It is a Dumbbell nebula and is located at a distance of 1,200 light years from our earth.

The Pillars of Creation of the Eagle Nebula no longer exist. They were destroyed some 6000 years ago by a nearby supernova explosion. The reason we still see the non-existent Pillars of Creation is that they were actually located at a distance of 7,000 light years from us. Since light takes time to travel, what we see is actually an image from the past.

The light that had already traveled for (7000 – 6000 = 1000 light years) before the supernova explosion took place is still reaching us. Thus, we will continue to see the Pillars of Creation till 2995 CE (remember that NASA first detected the Pillars of Creation back in 1995 using Hubble Space Telescope).

Nebulae that are outside the confines of our Milky Way are known as extra-galactic nebulae.

A nebula (Latin for "cloud" or "fog";[2] pl. nebulae, nebulæ, or nebulas) is an interstellar cloud of dust, hydrogen, helium and other ionized gases. Originally, the term was used to describe any diffuse astronomical object, including galaxies beyond the Milky Way

The Andromeda Galaxy, for instance, was once referred to as the Andromeda Nebula (and spiral galaxies in general as "spiral nebulae") before the true nature of galaxies was confirmed in the early 20th century by Vesto Slipher, Edwin Hubble and others.

Most nebulae are of vast size; some are hundreds of light years in diameter.

A nebula that is barely visible to the human eye from Earth would appear larger, but no brighter, from close by

The Orion Nebula, the brightest nebula in the sky and occupying an area twice the diameter of the full Moon, can be viewed with the naked eye but was missed by early astronomers.