Which heavenly bodies are commonly invisible due to their smaller size?

Meteoroids are indeed commonly invisible due to their smaller size. Meteoroids are defined as small rocky or metallic bodies in outer space, significantly smaller than asteroids, which are typically larger and can be observed more easily. When discussing visibility from Earth, meteoroids often enter the Earth's atmosphere and become meteors, which can create visible shooting stars. However, the actual meteoroids themselves are not typically detected unless they are large enough to create a noticeable event upon entering the atmosphere or unless they are captured by telescopes specifically designed to observe such small objects.

In contrast, asteroids and comets can often be observed because they are larger and can reflect sunlight, making them visible from Earth with the right conditions. Stars are enormous celestial bodies that emit their own light and can be seen from vast distances, making them very visible compared to the minuscule size of meteoroids. Thus, meteoroids' smaller size contributes directly to their relative invisibility compared to these other types of celestial bodies, highlighting the reason why they are usually not seen unless specific observational conditions are met.