A Nebula is a giant mass of cloud and dust that can be light years across such as the Snake Nebula which is a 3 light years across. They can be visible, although not seen clearly with the naked eye. There are five types or to put it another way, classifications of Nebulas out there, they are HII, reflection, planetary, supernova remnants and dark. These objects of gas can mark the beginnings of or end of Stars and both.
Let me explain, when a star dies, the left over materials can go onto recreate a new star somewhere. An exploding star is believed to be what caused the creation of the Solar System but more on that later.
Whilst most nebulas are invisible to the naked eye, it is possible to just about see the Orion Nebula. The names that Nebulas are given are because they look similar to real life objects, the Witch Head Nebula as seen below is because it looks vaguely like a witches head.
These large nebula areas of gas and dust are collapsing to form new stars. The Eagle Nebula in the constellation of Serpens is an example of where stars are being formed. The process to a fully fledged star system will take many millions or even billions of years before it becomes a solar system like ours. Diffuse Nebulae are some referred to as HII because they consist of highly ionized hydrogen. Ref: SEDS
The area where we are was probably in a Diffuse Nebula before it collapsed and the Sun was formed. In addition to the Sun, there would probably have been another star which went supernova and created the planets and elements that we find in the Solar System.
A reflection nebula is a dark nebula but it is visible because light from a nearby source is being reflected off it hence its name. The source of the light could be either from something that is behind it, another nebula or a star.
A well known Reflection Nebula is the Witch Head Nebula where it is reflecting light off Rigel, a nearby star. The Nebula lies about 800 light years away in the constellation of Orion and is about 50 light years across.
The Nebula is blue in nature because dust that causes their light tends to be more efficiently reflected. The same colour physics that applied to Witch-Head also applies to why our sky is blue. Ref: N.A.S.A.
Despite its name, planetary nebulae aren't anything to do with planets. They get their name from the British astronomer William Herschel, Sir who when he first saw a planetary nebula, he thought it looked like Uranus.
Planetary Nebulae are created when a star comes to the end of its life. When the star collapses, it might not explode like a supernova but expand and die like the Ring Nebula in the constellation of Lyra. The Ring Nebula and a lot of others will contain a white dwarf at the centre. Ref: University of Utah
When a star supernovas, it can create a nebula which is similar to the planetary nebula above. The difference can be explained by the type of star that produced the explosion. With a Supernova Remnant, the star that would produce the explosion would be about 8 or more times our son. Anything smaller would create a planetary nebula. Ref: Cornell. The image is of the Crab Nebula, which despite its name is not in Cancer but is in Taurus.
A pulsar can be found in the centre of a Supernova Remant. The streams that are spun out from the pulsar can light up the nebula. The Crab Nebula as mentioned previously has a pulsar at its core, imaginatively named Crab Pulsar.
The Dark Nebula is so dark and dense that light can not get through. They can be a large concentration of gas and dust that don't reflect the light that reaches them. They are also referred to as Absorption Nebula because they absorp the light that hits them.
The most well known example of a dark nebula is the Horse Head nebula in the constellation of Orion. Although when you look at the horse head images, you will often see the horse head as a stand alone nebula but it is in fact, part of a much larger nebula as the picture besides shows you the whole picture.
An Emissions Nebula is a cloud of ionized gas or plasma which is emitting light normally because of a star that is nearby or is at the centre of the Nebula. These nebula's appear reddish mainly but can appear blue and in violet as well, depending on the light and radiation that is hitting it. The Veil Nebula Nebula is an example of a Emissions Nebula. A Reflection Nebula which seem similar contains dust in addition to the gas. Ref: Answers
An Emissions Nebula produces its own light whereas a Reflection Nebula glows because of light that has come from a source outside the Nebula.
It is theorized that the Solar System was created from a nebula billions of years ago. The universe is 13.8 billion years old and the the generally accepted view is that the Sun and the Solar System is only 5 billion years give or take. Therefore what was happening in the eight billion years between the start of the Universe and the start of the Solar System?
The theory is that the space that we are in now used to be a huge gaseous/dust nebula but then collapsed in on itself by an external event, possibly a supernova event somewhere nearby. The minimum safe distance to quote EarthSky is 50 to 100 light years so its quite possible that that could have happened. An early star could have been the flame to start the nebula to collapse.
If the supernova is the cause, where's the supernova remnant to show for it? There doesn't seem to be a mention on the internet of what supernova remnant could have caused the start of our solar system. The Eagle Nebula, a star forming nebula is large, its about 70 light years by 55 light years according to Space . Given how big the Eagle Nebula is, the nebula that created us could be just as big and a result, it could have created other nearby stars such as Rigil Kentaurus which is better known as Alpha Centauri. Rigil Kentaurus inhibits a number of similarities to the Sun, they're about the same age give or take. It not unusual for a nebula to create multiple stars, that might even be the norm, for example, the Carina Nebula has 14,000 in its region Ref: N.A.S.A..
A star will start off with hydrogen and then convert that gas into helium through nuclear processes. Once all the hydrogen is used up, it'll convert the helium to lithium then keep moving up the periodic table until it gets to Iron (26) at which point it'll go supernova and explode. The heavier elements such as Silver, Gold, Mercury and Lead for example can only be created in a supernova explosion. Therefore the heavier elements would have been created by the exploding supernova and been captured by our collapsing nebula. Ref: Science Learning
Relax, its not going to happen for billions of years, we'll be long gone. In fact, it will not happen, the Sun will not turn into a supernova because according to Harvard is not massive enough. The Sun will eventually collapse back on itself and become a white dwarf. Ref: Live Science
By no means a complete list of Nebuas, the below list is just a sample of the nebulas out there.
|Saturn Nebula||Planetary Nebula||Aquarius|
|Helix Nebula (NGC7293)||Planetary Nebula||Aquarius|
|Heart Nebula||Emission Nebula||Cassiopeia|
|Wizard Nebula (NGC7380)||Nebula||Cepheus|
|Ghost Nebula||Bright Nebula||Cepheus|
|IC 5146||Reflection/Emission Nebula||Cygnus|
|North America Nebula (NGC7000)||Emission Nebula||Cygnus|
|Ghosthead Nebula||Emission Nebula||Dorado|
|Cat's Eye Nebula (NGC 6543)||Planetary Nebula||Draco|
|Witch Head Nebula (NGC1909)||Reflection Nebula||Fornax|
|Eskimo Nebula||Planetary Nebula||Gemini|
|IC 418||Planetary Nebula||Lepus|
|Red Rectangle Nebula||Protoplanetary Nebula||Monoceros|
|Cone Nebula (NGC2264)||Dark Nebula||Monoceros|
|Engraved Hourglass Nebula||Planetary Nebula||Musca|
|Little Ghost Nebula||Planetary Nebula||Ophiuchus|
|Flame Nebula (NGC2024)||Emission Nebula||Orion|
|Horsehead Nebula (NGC2023)||Dark Nebula||Orion|
|The Great Orion Nebula (M42, NGC1976)||Emission/Reflection Nebula||Orion|
|De Mairan's Nebula (M43, NGC1982)||Emission/Reflection Nebula||Orion|
|Messier 78 (NGC2068)||Reflection Nebula||Orion|
|The Little Dumbell, Cork or Butterfly Nebula (M76, NGC650)||Planetary Nebula||Perseus|
|California Nebula||Emission Nebula||Perseus|
|Statue of Liberty Nebula (NGC3576)||Nebula||Sagittarius|
|Red Spider Nebula||Planetary Nebula||Sagittarius|
|Omega Nebula (M17, NGC6618)||Diffuse Nebula||Sagittarius|
|Trifid Nebula (M20, NGC6514)||Emission/Reflection Nebula||Sagittarius|
|Spiculum, Lagoon Nebula (M8, NGC6623)||Emission Nebula||Sagittarius|
|Butterfly Nebula (NGC6302)||Planetary Nebula||Scorpius|
|Cat's Paw Nebula (NGC6334)||Emissions Nebula||Scorpius|
|Eagle Nebula (M16, NGC6611)||Star Forming Nebula||Serpens|
|Merope Nebula (NGC1435)||Reflection Nebula||Taurus|
|Owl Nebula (M97, NGC3587)||Planetary Nebula||Ursa Major|
|Dumbell Nebula (M27, NGC6853)||Planetary Nebula||Vulpecula|