What defines a deep sky object?

Deep sky objects are characterized by their great distances from Earth and are typically not visible to the naked eye without the aid of telescopes. These objects include galaxies, nebulae, and star clusters, which exist beyond our solar system, often at vast distances that render them faint and difficult to observe without magnification.

The correct answer emphasizes the nature of deep sky objects as remote entities, highlighting the necessity of telescopic assistance for observation. This classification sets them apart from celestial bodies that are easily visible within our solar system, such as planets and the Moon, which can be seen with the naked eye, or stars that are generally recognized as visible points of light in the night sky. Additionally, deep sky objects can encompass a wide variety of formations and phenomena located far beyond the limits of our solar system. Thus, they require telescopes for detailed observation and study, further reinforcing the definition provided by the choice.