According to mythological beliefs, Moon was married to the 27 daughters of Daksh Prajapati, who is considered to be the embodiment of Brahma, and the 27 constellations in the Hindu calendar are actually Moon's wives.
Rohini is also one of those constellations and here Rohini is the beloved wife of Moon; He did not have much affection for the other wives and the remaining daughters of Daksh Prajapati had to suffer neglect about which they all told their father. Daksh Prajapati told Chandrama that you are doing this wrong, you are married to all my daughters, so it is your duty to take equal care of everyone.
But Chandrama refused saying that you cannot control my mind and I abandon your other daughters and started taking Rohini with him. Seeing all this, Daksh Prajapati became angry and cursed the Moon with a terrible disease which would make them completely extinct.
To save himself from this, Chandra worshiped Lord Shiva and asked for his help. Then Lord Shiva, who was an expert in Sanjeevani Vidya, said that he could not completely free him from the curse but would help him in maintaining his existence and one day such a thing would happen. The time will come when they will become completely extinct. And saying this, Lord Shiva placed the moon on his head due to which he came back to his normal form (and from here Lord Shiva got the name Chandrashekhar) but as per the curse of Amavasya, he would have become completely extinct.
And from then onwards the Moon adopted all the daughters of Prajapati. But whenever he goes to his other wives, his size gradually decreases but the day he is with Rohini, he is in his full form i.e. on the full moon night.
I really like this story, whenever I look at the full moon, I feel as if the moon is with Rohini today.
Although there are complete studies available in science about the rise and fall of the Moon and how its shape changes, but this story attracts me more.