I have noticed a regrettable trend toward using the short "e" when pronouncing "the" before words beginning with a vowel: "thuh Earth"; thuh older one". This used to be a cultural symbol (e.g., old movies) of illiteracy and still sounds so to me. Is there any specific recommendation on this other than taste and pleasing the ear?
Meriam-Webster has an excellent suggestion on the pronunciation of "the":
before consonants usually thə, before vowels usually thē, sometime before vowels also thə; for emphasis before titles and names or to suggest uniqueness often ˈthē
In other words, if you want emphasis, go with the long "e"; and if you feel the pronunciation requires it, use the long "e" before vowels.