Nebulae are often the sites of star formation. In fact, all stars, planets, and solar systems are formed from nebulae. A nebula may lie undisturbed for many millions or billions of years as it waits for just the right conditions. Eventually, the gravity from a passing star or the shock wave from a nearby supernova explosion may cause swirls and ripples within the cloud. Matter begins to coalesce into clumps and grow in size. As these clumps get larger, their gravity increases. Gravity continues to pull in matter from the nebula until one or more of the clumps reach critical mass. The clumps are forming protostars. As gravity squeezes even tighter, the core temperature eventually reaches 18 million degrees. At this point, nuclear fusion begins and a star is born. The solar wind from the star will eventually blow away all of the excess dust and gas. Sometimes other smaller clumps of matter around the star may form planets. This is the beginning of a new solar system. Several nebulae have been found to be stellar nurseries. The Eagle Nebula, and the Orion Nebula are both sites of active star formation.
The Eagle Nebula
The Orion Nebula
There are a few nebulae that can be seen with the naked eye and many more that can be detected with a good pair of binoculars. A telescope is required to bring our fine details. Unfortunately, the human eye is not sensitive enough to bring out the rich colors of most nebulae. It is the photograph that does the most justice to these incredible objects. Until recently, time exposures on film were the best way to bring a nebula's true colors. Today, digital photography has simplified the process. New tools like the Hubble space telescope are giving us views of nebulae that have never been seen before. Areas of active star formation have been identified in many galaxies that were once thought to be inert.
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