Dark Nebulae

A dark nebula is a cloud of dust and gas as all nebulae are and are similar to reflection nebulae. The main difference is the perspective of the observer. If the illuminating star is in front of the dust cloud, then we see a bright reflection nebula, but if the cloud is in front of the star and the star's light cannot penetrate the cloud, then a dark nebula is formed.

The most famous example of a dark nebula is the Horsehead in Orion. Located north of the Great Orion Nebula, the Horsehead is a protruding dark cloud that forms the silhouette of a horse's head. The nebula sits near the gas cloud that forms the reflection nebula IC 434. The nearby star Sigma Orionis illuminates the nebula. The gas that forms both the dark nebula and the reflection nebula are probably the same dust and gas cloud. That portion which forms the Horsehead sits between Earth and Sigma Orionis while that area which forms the reflection nebula sits behind it. The geometry of this arrangement is not unlike what causes Mercury or Venus to show us more and more of their dark sides as they move from behind the Sun to a position in front of it.

Dark nebulae are among the most difficult objects in all the heavens to observe because frankly, they're dark. Your only hope of being able to find one is if the source that silhouettes it from behind close enough and bright enough to create the required contrast without being so bright that it washes out the dust cloud. Finding such nebula can be the ultimate test of your observing skills.

Now let's take what we learned about distant groupings of stars and the various nebula that represent the birthplaces and tombstones of stars and go and explore them. We'll see what makes them special and why they are important to us. Open clusters represent some of the youngest stars in the galaxy and diffuse nebulae represent the birthplace of those young stars. Planetary nebulae show where stars of modest mass puff away most of their mass as they die a relatively placid death. Supernovae remnants are where the universe's most cataclysmic deaths take place. Let's go explore some of them.

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Telescopes Mastery

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