Sleep (or lack there of!)

Why do babies like to be up at night?  What's so special about that time of day?  All day long Little One is fabulous.  Sleepy mornings.  Interactive smiles after lunch.  More sleeping in the afternoon.  Bath time and play time in the evening. And then comes the night.  Last night we were up until midnight, then up again from 2-5am.  And NOTHING would calm her down or entice her back to sleep.  Why oh why!  I'm loving being a mommy, but I think I'd love it more if sleep were a more regular part of my life.