Why is outer space black when almost all areas of the sky is covered by stars? Like the Hubble Space Telescope has proven us, everywhere in the sky there is stars
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Surprisingly, through observations made on the New Horizons mission, outer space is not black and might be brighter than we think. (Lauer 2021, "New Horizons Observations of the Cosmic Optical Background", The Astrophysics Journal)

Researchers went through images taken by the spacecraft's simple telescope and camera and looked for ones that were incredibly boring, the so-called "blank space" images, and subtracted all known source of light, including lights from stars, scatter light from the Milky way, and even light from hypothesized galaxies, and they are still left with plenty of unexplained light almost equivalent to the number of known lights.
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Why is this light not visible when looking up at the sky?
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The unexplained light observed by the New Horizons spacecraft isn't easily visible when looking up at the sky for several reasons:

1. Human eye sensitivity: The human eye has limited sensitivity to low light levels. The unexplained light detected by the New Horizons spacecraft is very faint, and it's below the threshold of what our eyes can typically detect.

2. Light pollution: In most populated areas on Earth, artificial light from cities, streetlights, and other sources creates light pollution, which can significantly reduce the visibility of faint celestial objects. This light pollution can make it difficult to see the dimmest stars and other faint sources of light in the night sky.

3. Atmospheric interference: Earth's atmosphere absorbs and scatters some of the light from celestial objects before it reaches the ground. This effect is more pronounced for fainter sources of light, which makes it even harder for us to observe the unexplained light sources detected by the New Horizons spacecraft.

4. Distribution of the light: The unexplained light is spread out over the entire sky, and it doesn't come from specific point sources like stars or galaxies. This diffuse nature of the light makes it difficult to distinguish it from the background sky.

It's important to note that the unexplained light detected by the New Horizons spacecraft is still an ongoing area of research. Scientists are trying to understand the origin of this light and its implications for our understanding of the universe.
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