The Definite Article ال
"When the ل in ال is followed by one of the moon letters, it automatically takes a sukoon and it is pronounced. However, when the ل in ال is followed by one of the sun letters, it becomes silent and it's not pronounced, also a shadda must be written on the sun letter."
My problem is about memorizing these letters. I always connect incorrectly when reading ال with the sun and moon letters. Is there an easy way to know them or do I have to just memorize them?