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The pronunciation of any word in English (or any language at all) is not Universal.  This is because there are many different dialects of The English Language — both throughout America, and also world-wide.  The pronunciations that are presented on GiveMeSomeEnglish!!! are based-upon a combination of both “common usage”, and the most neutral accent used in The International Common Tongue — a.k.a. “American English”.
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Astronaut – For this word:  the “A” is short;  the “t” is pronounced like the “ch” combination (this is due to the placement of the letter “r” directly after it);  the “o” is pronounced as a true-schwa;  the “au” combination is pronounced like the “aw” combination;  and the final “t” is (often) stopped.

– /æS-chrə-naw[t]/ – /ˈæs.tʃɹə.nɔ[t]/ – Notice also that the stress is on the first syllable –

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Learn More About The Word “Astronaut” On Wiktionary

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