Moon represents the automatic response to situations without preceeding conscious forethought (Mercury). You 'feel' it inside before saying or doing something. It's similar to an inherent feeling of 'been there, seen it, done it all before'. This makes it react accordingly to those outer situations confronting it through the characteristics of the sign it is in. In your case....in an Aries manner.
Sun can be more of a 'whooooa'. Is this really what I want? Yet also the drive of 'yes, this is what I want.' It learns through outer experiences to express and be itself, as per natal Sun sign. For you, that's Capricorn.
Aries to Capricorn can be like reigning in impulsiveness and/or just as easily following those inherent instincts, to take the time to achieve what is wanted.
An interesting situation can occur when the Sun of one person is in the same sign as the Moon of another, and each is confronted with its mirror image.
It happened to me when working with a colleague whose Sun sign was my Moon sign, who made the remark, 'I want to be .......'. My instant inner feeling response was followed by the thought, 'but I'm already like that!'
Another colleague and I, same situation, have remained life-long friends. She is still 'so submissive' in many ways that inwardly makes my outer hairs stand on end! She has the typical of the Sun sign complaints that give her much physical pain. I've always felt (though don't ask) that her Sun sign has not lived and shone in the manner it would have desired.
My Moon sign is my mother's Sun sign. I recognise so much of her in me, as well as looking at her image in my mirror.