Sun and moon letters
In Arabic and Maltese, the consonants are divided into two groups, called the sun letters or solar letters (Arabic: حروف شمسية ḥurūf shamsīyah) and moon letters or lunar letters (حروف قمرية ḥurūf qamarīyah), based on whether or not they assimilate the letter lām (ﻝ l) of a preceding definite article al- (الـ). These names come from the fact that the word for 'the sun', al-shams, pronounced ash-shams, assimilates the lām, while the word for 'the moon', al-qamar, does not.
When followed by a sun letter, the /l/ of the Arabic definite article al- assimilates to the initial consonant of the following noun, resulting in a doubled consonant. For example, for "the Nile", one does not say al-Nīl, but an-Nīl. When the definite article is followed by a moon letter, no assimilation takes place.
The sun and moon letters are as follows:
The letter ج jīm is pronounced differently across the varieties of Arabic, most often representing a coronal consonant such as [d͡ʒ] or [ʒ]. However, in Classical Arabic, it represented a palatalized voiced velar plosive, /ɡʲ/ or a voiced palatal plosive /ɟ/. As a result, it was classified as a moon letter and it never assimilates the article. In varieties where ج is pronounced [ɡ], the sun letters still form a natural class since they comprise all coronal consonants.
In the written language, the ال al- is retained regardless of how it is pronounced. When full diacritics are used, assimilation may be expressed by putting a shaddah on the consonant after the lām, and non-assimilation by placing a sukūn over the lām.
|Sun letters||Moon letters|
|الشَّمْس||ash-shams||'the sun'||الْقَمَر||al-qamar||'the moon'|
|الثِّقَة||ath-thiqah||'the confidence'||الْمُرْجَان||al-murjān||'the coral'|