Light exists on a spectrum of frequencies extending from gamma rays at the highest frequencies to radio waves at the lowest, though human eyes are sensitive to only a narrow range of frequencies in the middle known as the visible spectrum. The different colors we see correspond to the different frequencies of light within that range. Given that there are so many frequencies of light, one might wonder why our eyes didnt evolve to be sensitive to more frequencies.

Gamma rays from space collide with Earth's atmosphere, which converts some of their energy to heat and creates a distinctive cascade of subatomic particles down toward the ground. However, the rays themselves are entirety absorbed before they can reach Earth's surface. Thus, Earth would appear to be pitch black to eyes that were only sensitive to gamma rays. Similarly, the majority of frequencies of light that are higher or lower than those in the visible spectrum—such as ultraviolet and most infrared frequencies, respectively—are mostly or entirely absorbed by Earth's atmosphere.

One reason we see the frequencies we do is that visible-spectrum light generally passes through our atmosphere without being absorbed or reflected. Another reason is that the Sun, in some respects an average star, emits most of its light at frequencies in the visible spectrum, whereas a hot star emits most of Its light at ultraviolet frequencies and a very cool star emits most of its light at infrared frequencies. Indeed, to remarkably high precision, the human eye to most sensitive to the exact frequency in the yellow part of the spectrum at which the Sun is the brightest

Even if there are living beings on other planets, it is not likely that they would see mainly at very different frequencies than we do. Virtually all gases that are abundant in the cosmos tend to allow frequencies in the visible spectrum to pass through while absorbing other frequencies, and all but the coolest stars put out much, If not most, of their light in the visible spectrum. If there are Irving beings on other planets, they probably see at roughly the same frequencies as we do, though there may be occasional exceptions.