I'm trying to learn how to read Arabic and I noticed that sometimes the letter Laam (ل) is either silent or takes the pronunciation of the following letter, as in this text from Wikipedia:
As-salāmu ʿalaykum (Arabic: السَّلَامُ عَلَيْكُمْ [asːaˈlaːmu ʕaˈlajkum]) is a greeting in Arabic that means "peace be upon you".
To me it looks like "al-salamu ..." and not "as-salamu ...".
What is the general rule here?
Update: This question is similar to another question about "sun and moon letters". The body of that question answers this one, and builds upon it by asking the reason for the convention.
There seems to be little interest in reopening this question (which has already been answered to my satisfaction). I just wanted to reference my Meta Stack Exchange question that references this one and collects other examples of what I might consider "false duplicate" pairs: When are questions which build upon each other considered duplicates?