Here's why:
* Stress: The emphasis in the word "Saturday" falls on the second syllable, "ur". This makes the first syllable "Sat" unstressed.
* Vowel Reduction: In unstressed syllables, vowels often become reduced to a schwa sound (ə). This is the case with the "a" in "Sat".
So, while the word is spelled "Saturday", it's pronounced more like "Sat-ər-day".