Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. In this breathtaking view from the space shuttle Endeavor , the Sun is just visible peaking over towering anvil-shaped storm clouds . The silhouetted cloud tops mark the upper boundary of the troposphere, the lowest layer of planet Earth's atmosphere . Sunlight filtering through suspended dust causes this dense layer of air to appear red. In contrast, the blue stripe marks the stratosphere, the tenuous upper atmosphere, which preferentially scatters blue light.
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