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--- un:nebula [2024/04/17 06:01] – [1.1 Bright nebula] asad
+++ un:nebula [2024/04/17 06:04] (current) – [1. Types of nebulas] asad
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 Nebulas can be either **bright** or **dark**.  Bright nebulas are seen against the background of a darker sky, but the dark nebulas are seen in silhouette against a brighter background. There are two types of bright nebulae: emission and reflection. The gas in an emission nebula radiates its own light, but the reflection nebulas are seen mainly because they reflect the light coming from nearby stars.
+Sometimes protoplanetary disks are also called protoplanetary nebulas, the gas and dust surrounding a protostar that will soon give rise to planets and asteroids. However, the usage getting out of fashion and these objects are now mainly known as //proplyds//.
 ==== - Bright nebula ====
 === Emission nebula ===
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 ==== - Dark nebula ====
+They are also known as absorption nebulas because they absorb the light coming from neighboring stars. The absorbed visible light is then either scattered or re-emitted at infrared wavelengths. A famous example is the Horsehead nebula which is seen below in the infrared vision of Hubble.
 {{:un:horsehead.webp?nolink&600|}}