Thara /Taara dosham
Simply means undesirable inter constellational (Nakshatra) relationship while analyzing marriage compatibility between the couples and for fixing muhurtham for marriages
When the birth stars of the Sthree and Purusha are same as Bharani,Aslesha,Swathi,Jeshta,Mo ola,Sathabisha,Dhanishta, And Purva bhadrapada are undesirable
Purusha Nakshatra happens to be the 3rd.,5th,and 7th. from Sthree Nakshatra Undesirable
Mrigairas,Chitra and Dhanishta (Siro rajju)and Rohini,,Ardra,Hasta,Swathi,Sravana and Sathabisha (Kanta rajju)are mutually undesirable
Bharani, and Revathi are undesirable to Purva bhadrapada and Dhanishta, U.palguni and U.bhadrapada are undesirable to Visaka and Citra
These are only a few examples. There are many similar inter constellational (Nakshatra) relations considered as undesirable
While deciding muhurthas in case the the tara balam happens to be bad (1,3,5 and 7) and the tara falls in First Navakam for Janma Tara, Second Navakam for Vipat Tara, and Third Navakam for Pratyak Tara and in any Navakam for Naidhana has to be discarded as Undesirable Thara dosham
