Because the infrared light used by NASA's Spitzer Space Telescope to photograph this, the North America Nebula, can penetrate dust, the continent for which this "swirling landscape of stars" is named has disappeared from view. "Dusty, dark clouds in the visible image become transparent in Spitzer's view," NASA explains of the phenomenon. "In additiona, Spitzer's infrared detectors pick up the glow of dusty cocoons enveloping baby stars."
The "baby stars" NASA mentions are the clusters of one-million-year-old stars scattered throughout the image. Visible, too, are many slightly older stars (in the three-five million year range). "Some areas of this nebula are still very thick with dust and appear dark even in Spitzer's view and are likely to be the youngest stars in the complex (less than a million years old)," according to NASA.
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