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| Bright nebula are clouds of gas that shine either by reflected starlight or by light emitted due to the interaction of charged particles and interstellar radiation. Dark nebula are clouds of dust or colder gas. You can see them because they form a silhouette against brighter objects behind them along the line of sight. These objects can be very colorful. They are often large and difficult to capture in one CCD frame. Some are relatively bright and easy to image. Others are very dim and have a very low surface brightness. These are much more difficult to image, sometimes requiring hours of exposure time. |
