The brightest luminary in the sky, causing the change of day and night on Earth, is the Sun. The second brightest luminary can also be easily observed during the day, and in the night sky it surpasses all other luminaries combined in brightness. It is the only natural satellite of the Earth, the Moon. The third luminary is the brightest point (star-like) object. This object can also be observed (albeit stratum) during the day. It is the brightest of the planets Venus.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.