One way to paradise

Definite Article – اَلْ

In this section we will learn some new vocabulary and we shall also learn the rules relating to the sun and moon letters. The most important point to understand with this rule is that it governs the spoken (pronunciation) Arabic and not the written word.
Arabic has 28 letters. Of these 14 letters are called Solar Letters, and the other 14 are called Lunar letters. In the articulation (speaking) of the Solar letters, the tip or blade of the tongue is involved as in t, n, r, s, etc. The tip or blade of the tongue does not play any part in the articulation of the Lunar Letters as in b, w, m, k etc.
When /alif-lām/ “al” is prefixed to a noun beginning with a Solar letter, the “l” of “al” is assimilated (joined) to the Solar Letter, e.g. al-shamsu (the sun) is pronounced /ash-shamsu/.
No change takes place in writing اَلشَّمْسُ. The assimilation is indicated by the /shaddah/ on the first letter of the noun after “al”.
No such assimilation takes place with the Lunar Letters, e.g. /al-qamaru/ (the moon) is pronounced /al-qamaru/ اَلْقَمَرُ. Here are some more examples of the assimilation of the “l” of “al” to the Solar Letters (don't worry about the meanings of the words yet):

Note that the “a” of “al” is pronounced only when it is not preceded by another word. If it is preceded by a word it is dropped in pronunciation, though it remains in writing, e.g. /wal-baitu/. Here the “a” is dropped and the phrase is pronounced /wal-baitu/ not /wa al-baitu/. To indicate this omission in pronunciation, this sign: () is placed above the /alif/.
The initial vowel (a, i, or u) which is omitted when preceded by a word is called /hamazatu l-wasl/.
We have learnt that the /tanwīn/ is the indefinite article, and it is to be translated as “a” e.g.: بَيْتٌ means a house. This rule does not apply to adjectives like مَفْتُوحٌ "open", and مَكْسُورٌ "broken".