If there is a vowel sound after a ‘the’ means that the is pronounced ‘thee’
How to Pronounce “the” in English
Normally, we pronounce “the” with a short sound (like “thuh”). But when “the” comes before a vowel sound, we pronounce it as a long “thee”.
|vowel sound||we write||we say|
|A||the apple||thee apple|
|E||the egg||thee egg|
|I||the ice-cream||thee ice-cream|
|O||the orange||thee orange|
|U||the ugli fruit||thee ugli fruit|
It is important to understand that it is what we say that matters, not what we write. It is the sound that matters, not the letter used in writing a word. So we use a long “thee” before a vowel sound, not necessarily before a vowel. Look at these cases:
|we write||with||we say||with|
|the house||consonant (h)||thuh house||consonant sound|
|the hour||consonant (h)||thee our||vowel sound|
|the university||vowel (u)||thuh youniversity||consonant sound|
|the umbrella||vowel (u)||thee umbrella||vowel sound|
Emphatic the [thee]
When we wish to place emphasis on a particular word, we can use “emphatic the” [thee], whether or not the word begins with a consonant or vowel sound. For example:
A: I saw the [thuh] President yesterday.
B: What! The [thee] President of the United States?
A: Yes, exactly.
This lovely explanation came from http://www.englishclub.com/pronunciation/the.htm