"There is a bird in the sky."
Translation:आसमान में पक्षी है ।
Good question. पक्षी आसमान में है would mean "The bird is in the sky." Hindi sentences typically begin with what is called the topic of the sentence. The topic is usually a definite thing, person or place that the rest of the sentence describes. It's the component of the sentence that the narrative flows from.
In "There is a bird in the sky", "the sky" is definite, and the presence of a bird adds information about the sky. So "the sky" is the topic of the sentence, and when translating into Hindi, it comes at the beginning: आसमान में (एक) पक्षी है।
In "The bird is in the sky", the narrative is about the bird, and it flows from "the bird" to "the sky", hence the topic is "the bird", and therefore this time it comes first: पक्षी आसमान में है।
Oh, I see. पक्षी and पंछी can be used to refer to any bird. चिड़िया, as far as I know, is only loosely used for birds in general (kind of like the English "fowl"—not saying चिड़िया and "fowl" are synonymous) but is mostly used when talking about small birds. So, a house sparrow, a bulbul, a swallow, a sunbird, etc. can all be called चिड़िया but I don't think a peacock, a goose, or a flamingo can. This article says चिड़िया derives from the Sanskrit word for male sparrow "चटकः".