Swami Dayanand Saraswati, in his book Rigvedadi Bhashya Bhumika on the authority of Rigved 1/164/33, uses immoral language to convey the working of the natural phenomenon. You can yourself assess the cheap nature of this allegory, which promotes and glorifies incest.
The Sun or the Sun's sphere is called Savitur (the begetter) and Prajapati (the Lord of creatures). Light and Dawn are like his two daughters. Metaphorically speaking the one which is produced from the other is like the offspring of the latter which is like the parent of the former. The Sun follows fast with his rays his daughter Dawn of a reddish complexion. Having seized her he begets upon her the Day which is like his sun. The Dawn is like the mother and the Sun like the father of this son, because the Sun with his rays, which are like hs semen, begets the Day, his son, upon her, the Dawn. The Dawn is the reddish light on the horizon in the 2 and half hours of night before morning. By the intercourse of the father and the daughter is born a son, the full light of the day. As a son is born by the intercourse of his father and mother, similarly, here (the Day is born by the intercourse of the Sun with the Dawn).
Similarly, the rain-cloud and the earth stand to each other in the relation of the father and the daughter. The earth is produced from the waters, hence, the earth is the daughter of the rain-cloud. The rain-cloud by pouring rain water upon her makes her conceive. That conception results in the production of vegetables, etc. as their offspring. This also is an allegory. This borne out by Vedic texts.
Light of day is my father- protector and begetter - the producer of all activities. There is a mutual relation between the two. This extended or venerable earth is my mother. The rain-cloud and the earth are like two armies arrayed against each other or like the awning and the floor. The father rain-cloud pours the waters upon his daughter - the earth and makes her conceive. This is merely an allegory.
Rigveda i. 164. 33.
The same allegory is described in the following Mantra.
The sun which is called Vahni makes his daughter, the said dawn, conceive by making his semen, the rays, flow into her and begets a son - the Day. Rig III. 31. 1.
[Rigvedadi Bhashya Bhumika, English translation; An Introduction to the Vedas by Ghasi Ram, pp 389-391]
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