Аль
The Arabic definite article is "al-" (i.e. the letter "alif" followed by ). The in "al-" is pronounced if the letter after it is (, lunar), but if the letter after it is (, solar), the after it becomes part of the following letter (is assimilated). "Solar" and "lunar" became descriptions for these instances as the words for "the moon" and "the sun" ("al-qamar" and "ash-shams", respectively) are examples of this rule.