The differences between 生日 and 生辰 Recently, I have come across people giving birthday wishes to others using the word 生辰 instead of 生日.

I looked up some online dictionary/translation tools and it turns out 生辰 also means birthday.

So what are the differences between 生辰，生日. By the way, do people also 生天 to mean birthday in Chinese?

Thanks,
生辰 can mean either "birthday"(the day one's birth) or 生日+时辰 (birthday + birth time) as in the phrase 生辰八字. 

Usually, 生辰 just means birthday, but it's more literary. You can probably only see it's used in a book. For example, 而这一日子恰逢其80岁生辰. Normally, people just use 生日 in spoken, but you can say 生辰 when you try to be more literary. 

生天 isn't a correct word for birthday. 生天 in old Chinese is the same as 升天, which means go to heaven.