Solar and Lunar letters in Arabic !

When reading in Arabic, there is something called "Al Al-ta'reef" "ال التعريف" which is same as "the" and its attached to the beginning of any noun.

sometimes when attaching "Al" then reading the word you find it difficult to pronounce the "L" clearly and sometimes not, thus the letters are divided into two groups

A group where you can pronounce the "L" easily "lunar letters":

if you attached the "Al Al-ta'reef" to the word "moon" in Arabic you will find it very easy to pronounce the "L":

القمر => Al Qamar

A group where you can't "Solar letters":

attaching the "Al Al-ta'reef" to the word "sun" in Arabic

الشمس => Al Shams

you find it much more easier to pronounce it without the "L" like saying "A Shams"

Conclusion:

Lunar letters are:

أ، ب، ج، ح، خ، ع، غ، ف، ق، ك، م، هـ، و، ي

Solar letters:

ت، ث، د، ذ ،ر، ز، س، ش، ص، ض، ط، ظ، ل، ن

hope this helps a bit :)