What do the first moon, the second moon, and the moon's shadow refer to respectively?

(1) Original text of the Śūraṅgama Sūtra, Volume Two: 佛告阿难。且汝见我。见精明元。此见虽非。妙精明心。如第二月。非是月影。 

Explanation: The Buddha told Ānanda: The seeing essence with which you can see Me is the origin that illuminates material form. Although this seeing essence is not the subtle, wondrous, luminous original mind, it is like the second moon, not the moon's reflection. 

Here the Buddha says that the second moon refers to the seeing essence's luminous origin, which includes the seeing of the six consciousnesses and the seven consciousnesses, but is not the most subtle and wondrous luminous mind of the seeing essence. That is to say, the seeing nature of the seeing essence's luminous origin is the seeing nature of the seven consciousnesses, not the tathāgatagarbha mind-substance. When the seeing essence is explicitly stated, it refers to the seeing nature of the six consciousnesses, but the seeing nature of the seventh consciousness, the manas, is hidden and not explicitly stated; in fact, it includes the seeing nature of the seventh consciousness. The seeing essence of the seven consciousnesses is neither substance nor form: it is neither the tathāgatagarbha's original substance—having no self-nature and no form or color—nor is it a shadow conjured by the tathāgatagarbha. The shadow refers to the images seen by the seven consciousnesses, which are composed of earth, water, fire, wind, and space. 

Original text of the Śūraṅgama Sūtra, Volume Three: 复次阿难。云何六入。本如来藏。妙真如性。阿难。即彼目睛。瞪发劳者。兼目与劳。同是菩提。瞪发劳相。因于明暗。二种妄尘。发见居中。吸此尘象。名为见性。此见离彼。明暗二尘。毕竟无体。 

Explanation: In the teaching on the falsity of the six sense bases (ṣaḍāyatana), the mark of heaviness (dauṣṭhulya-lakṣaṇa) arising from staring within bodhi is discussed: at the point where the faculties and the strain make contact, the seeing nature of the six consciousnesses arises. This seeing nature, when apart from the sense objects, has no substance; it has no self-nature and no autonomy. The seeing nature of the six consciousnesses at the six faculties is the second moon, the mark of heaviness arising from staring within the bodhi of the tathāgatagarbha. It does not come from anywhere else; it comes directly from within the bodhi of the tathāgatagarbha, arising from the seed of consciousness among the seven great seeds of the tathāgatagarbha. 

The mark of heaviness arising from staring within the tathāgatagarbha is like pressing on one's eyes with the hand: when the eyes become sore, fatigued, and weary, one sees objects with double images—one real and one false. The false one is the second moon, which comes from the real one; without the real there would be no false. To call it false, yet it is real; to call it real, yet it is false. For that false one, saying it is false is not right, and saying it is real is also not right—it is neither real nor false, yet both real and false; the image formed by pressing the eyes is also not a reflection. These marks of heaviness of the tathāgatagarbha are brought about by the manas. If the manas could become tranquil, the tathāgatagarbha would no longer strain, and then all the marks of heaviness—the seeing nature—would vanish and disappear.