The existence of Neptune is not solely dependent on direct visual observation by the majority of the human population. Instead, the discovery and confirmation of Neptune's existence are based on scientific observations, mathematical calculations, and a variety of indirect methods. Here are a few key points:
Mathematical predictions: In the early 19th century, astronomers observed irregularities in the orbit of Uranus, which suggested the gravitational influence of an unknown planet. Mathematicians Urbain Le Verrier and John Couch Adams independently calculated the approximate position and mass of this hypothetical planet, which later became known as Neptune.
Observational confirmation: Based on the predictions of Le Verrier and Adams, astronomers conducted targeted observations to search for the predicted planet. In 1846, the German astronomer Johann Galle successfully observed Neptune through a telescope following Le Verrier's calculations, confirming its existence.
Retroactive observations: Once Neptune was discovered, astronomers looked back at earlier sky survey data and realized that Neptune had been inadvertently observed but mistaken for a star on multiple occasions.
Orbital and gravitational effects: The existence of Neptune was further supported by studying its gravitational influence on other celestial bodies. The precise measurements of Neptune's mass, orbit, and gravitational effects on other planets, moons, and even spacecraft have been consistent with its predicted characteristics.
Space missions: The Voyager 2 spacecraft, which flew by Neptune in 1989, provided detailed observations and measurements of the planet, its atmosphere, rings, and moons, further confirming its existence.
While it's true that the majority of the human population has not directly seen Neptune with their naked eyes, the scientific process of observation, prediction, and confirmation, along with the extensive body of astronomical data and measurements, gives us a high level of confidence in the existence and properties of Neptune. This process is at the core of scientific inquiry, allowing us to expand our knowledge about the universe beyond what can be directly observed by individuals.