What does it mean to collect the aura of heaven and earth and the essence of Xiao Yi?

As the ancients said, immortals absorb the aura of heaven and earth and gather the essence of the sun and the moon in order to live a long life. In fact, this sentence is well-founded. The so-called atmosphere of heaven and earth refers to the weather (air) and the earth's atmosphere. The weather is sunny, and the ground gas is cloudy. The intersection of weather and atmosphere forms everything. Oxygen is the most basic element to maintain our life, which is handled by the sun and the moon.