Surya-Shani: Shani was not obedient to His father Surya, moreover Shani was son of Chaayaa, so Surya Deva did not like Him.
Rahu,Ketu-Surya,Chandra: Surya and Shashi told Narayan that the demon is drinking Amrta, so when Rahu, Ketu took incarnation, they disliked Surya,Chandra.
Guru-Shukra: Both were in childhood the disciples of same Guru Angirasa Rishi. But Angirasa Rishi showed bias and more fondness to his own son Brihaspati. So Shukra did not like Guru. Moreover there are several more accounts of Guru-Shukra enmity in various Scriptures.
Budha-Chandra: Here only Budha see Chandra as enemy whereas Chandra is friend of Budha. Budha dislikes his father Chandra because - Chandra abducted Tara,wife of Guru, and by their union Budha was born. Budha knowing this illegitimate reason of his birth does not like Chandra.
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What are the reasons of other enmity?
Between, Shani-Mangala, Guru-Budha, Chandra-Shani, Shukra-Chandra, Surya-Shukra And others.
Please correct me where I am wrong, but please tell me reasons also.