Sunlight is scattered by Earth's atmosphere. Blue wavelengths (~475 nm) scatter more than other colors due to Rayleigh scattering, making the sky appear blue to our eyes.

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what

What is the largest organ in the human body?

The skin is the largest organ, covering 1.5–2 square meters in adults and weighing about 3.6 kg. It has three layers: epidermis, dermis, and hypodermis.

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when

When did the universe begin?

The universe began approximately 13.8 billion years ago in an event called the Big Bang — an expansion from an infinitely dense, hot singularity. The cosmic microwave background radiation is its "afterglow."

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where

Where is the driest place on Earth?

The Atacama Desert in Chile is the driest non-polar place — some areas have received no measurable rainfall in recorded history. NASA uses it as a Mars analogue due to the extreme aridity.

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which

Which animal is the fastest?

The peregrine falcon is the fastest animal overall at 389 km/h in a hunting dive. On land, the cheetah reigns at 112 km/h — though it can only sustain top speed for about 460 meters.

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whose

Whose theory was E=mc²?

Albert Einstein derived E=mc² in 1905 as part of his Special Theory of Relativity. The equation means a tiny amount of mass contains enormous energy — forming the basis of nuclear physics.

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how

How big is the observable universe?

The observable universe has a diameter of about 93 billion light-years and contains an estimated 2 trillion galaxies. Despite being 13.8 billion years old, the expansion of space makes it much larger.

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