There are an enormous number of stars in the universe. A digital camera aimed at the nighttime sky will have many stars in every pixel of the camera's focal plane. Which of the following reasons does NOT contribute to the darkness of the night sky?
1. The universe is expanding and the frequency spectrum of the light from stars moving away from Earth is "red-shifted" and diminished in intensity.
2. The universe is permeated with electromagnetic waves, but very little is in the visible part of the spectrum.
3. A star's solid angle on Earth's surface is very small, due to its distance away from us.
4. Dark matter between the stars and Earth absorbs the starlight.
5. The universe is young (only 13.8 billion years old) and many stars would be so far away that their light has not had time to reach us.