Why are most stars invisible to the naked eye in a clear daytime sky?

Answer: Scattered sunlight makes the sky much brighter than faint stars.

Stars stop emitting light when sunlight reaches them. — Stars keep emitting light whether it is day or night where we stand. Daylight changes the brightness of our sky, not the stars’ energy production. Their faint light is difficult to distinguish against that bright background.

Earth’s air blocks starlight but lets sunlight through. — Air does not selectively block light just because it came from a distant star rather than the Sun. Sunlight scattered by the atmosphere creates a bright background. Stars remain beyond it, but their contrast is usually too low for our unaided eyes.

Scattered sunlight makes the sky much brighter than faint stars. ✓ — The atmosphere scatters sunlight across the sky, producing a bright background that overwhelms most stars for unaided eyes. After the Sun sets and the sky darkens, many become visible. Earth’s rotation also changes which stars are above the horizon; it is not the same set overhead all day and night.