Whereas I will muddy the waters a little, and explain that 'ann an/am' is 'in' as a complete phrase. It is not "in the" in any way, and it has the same meaning as just using 'an' (in). "In the" is 'anns + appropriate article'. In this case, 'anns an'. Do also note that it is Ògmhios, with accent and capital, since months are proper nouns and accented letters are not the same as unaccented.