From Mental Floss, Eight things you might not know about vowels.
My favorite tidbit:
THE MOST COMMON VOWEL IS SCHWA.
The most common vowel sound in English doesn’t even have its own letter in the alphabet. It does have a symbol, though, and it looks like this: ǝ. It’s the “uh” sound in an unstressed syllable and it shows up everywhere, from th[ǝ], to p[ǝ]tato, to antic[ǝ]p[ǝ]tory. You can discover nine fun facts about it here.
The link provided, btw, takes you to Nine fun facts about the schwa. Okay, and there it says:
A schwa is the ‘uh’ sound found in an unstressed syllable. For example, the first syllable in amazing (ǝ-MA-zing), the first syllable in tenacious (tǝ-NA-cious), the second syllable in replicate (RE-plǝ-cate), the second syllable in percolate (PER-cǝ-late), the first syllable in supply (sǝ –PLY), the first syllable in syringe (sǝ-RINGE). That’s a written A, E, I, O, U and even a Y coming out as schwa in the spoken version.