Sun and moon letters

In Arabic and Maltese, consonants are divided into two groups: the sun/solar letters (Arabic: حروف شمسية ḥurūf shamsiyyah, Maltese: konsonanti xemxin) and moon/lunar letters (حروف قمرية ḥurūf qamariyyah, Maltese: konsonanti qamrin).

Sun letters (red) and moon letters (black) in Arabic

In those languages, all nouns start with the word "al" (الـ) in Arabic or "il" in Maltese. Both words mean "the." If a sun letter comes after the consonant, the "l" sound in "al" or "il" is dropped and is replaced by whatever sound the letter makes. However, if a moon letter comes after, the "l" sound in those words stays.

In Arabic, the word for "the sun" is ash-shams because the "sh" sound is a sun letter. Meanwhile, the word for "the moon" is al-qamar because the "q" sound is a moon letter.

Rule

Below is a chart of the sun and moon letters in Arabic.

Sun letters	ﺕ	ﺙ	ﺩ	ﺫ	ﺭ	ﺯ	ﺱ	ﺵ	ﺹ	ﺽ	ﻁ	ﻅ	ﻝ	ﻥ
	t	th	d	dh	r	z	s	sh	ṣ	ḍ	ṭ	ẓ	l	n
Moon letters	ء	ﺏ	ﺝ	ﺡ	ﺥ	ﻉ	ﻍ	ﻑ	ﻕ	ﻙ	ﻡ	ه	ﻭ	ﻱ
	'	b	j	ḥ	kh	ʻ	gh	f	q	k	m	h	w	y

Writing

The ال 'al-' is written down in Arabic regardless of how it is pronounced. In the case of sun letters, a mark called the shaddah (ـّـ) is written over the sun letter. For moon letters, a mark called the sukun (ـْـ)is written over the letter ل lam in the al-.

Examples

Sun letters			Moon letters
الشَّمْس	'ash-shams'	'the sun'	الْقَمَر	'al-qamar'	'the moon'
الثِّقَة	'ath-thiqah'	'the confidence'	الْمُرْجَان	'al-murjān'	'the coral'

Maltese

Below is a chart of the sun and moon letters in Maltese.

Sun letters	ċ	d	n	r	s	t	x	ż	z
Moon letters	b	f	ġ	g	għ	h	ħ	j	k	l	m	p	q	v	w

If a word starts with any of the moon letters, the word il- stays the same. However, if it stats with a sun letter, the word il-changes to iċ-, id-, in-, ir-, is-, it-, ix-, iż-, iz-.

If a word begins with two consonants, it changes to "l-i-." For example, skola (school) becomes l-iskola (the school).