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Understanding brightness

The Helix Nebula provides a lesson in how size changes everything.
RELATED TOPICS: MAGNITUDE
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One of the first concepts the novice backyard astronomer needs to grasp is the idea of magnitude. The magnitude of a star defines its brightness and, therefore, its visibility. It’s easy to understand once you get used to the idea that the larger the magnitude number, the fainter the star. Although the brightnesses of clusters, nebulae, and galaxies are also expressed in magnitude, the numbers are deceiving. The Helix Nebula (NGC 7293) in Aquarius is a case in point.

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