The long ‘o’ sound is generally transcribed as the diphthong /c/ (schwa + upsilon) or /o/ (small case <o> + upsilon) in IPA phonetic symbology. Typical examples are ‘low’, ‘no’ & ‘go’. The short ‘o’ is /Z/ (a turned script A) as in ‘rock’, ‘or’ & ‘hot’. Please note some examples given have variant pronunciations.
The long ‘a’ is generally considered to be the diphthong /ew/ (small letter <e> + small capital letter <I>) as in ‘day’, ‘age’ & ‘face’. The short ‘a’ is /æ/ (an a-e ligature called ‘ash’) as in ‘hat’, ‘cap’ & ‘absent’.
Please note also the long ‘a’ sound is exactly how you utter the 1st Roman alphabet letter ‘A, a’. Similarly the long ‘o’ sound is how you say the alphabet ‘O, o’.