Hi Aravind, Famous for Abbey Falls, Talacauvery and Golden Temple (Namdroling Monastery), Coorg in Karnataka would serve your purpose in this case. The place is considered as one of the best hill stations with clear skies in Karnataka. You can enjoy a romantic night in jungles or normal stargazing in Coorg.
Another option can be Paradise Beach in Gokarna, a less visited placed place where you can wrap yourself in a sleeping bag and simply stargaze. Best,
Ishita