Reddish hydrogen emission regions, called HII regions, are the regions of intense star formation seen to lie mainly along M51's bright spiral arms.
红色的氢发射区域,称为HII区域,是激烈的恒星形成区,主要沿着M51明亮的旋臂可见。
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One result is that M101, also called the Pinwheel Galaxy, has several extremely bright star-forming regions (called HII regions) spread across its spiral arms.