get_categories() returns an array of object?

After reading some topics on Codex, I found out that I can use $cats=get_categories(); to obtain an array of categories.
But each of the array is an object.
By referring to the examples I got to know that the object has a field like this: $cat->cat_name

What if I want to know other fields in this object?
Is there anything I can refer to?

I’ve also got questions like this when using WP_Query to query some thing.
I didn’t know what to do with the result of the query, either.