Why is Rosh Chodesh of some months the day after the new moon, opposed to the night of the new moon?

I was looking through my calendar earlier and had to keep double checking because the new moon falls on the night of February 27th however Rosh Chodesh Adar is on the night of February 28th. I also noticed the same thing for every Rosh Chodesh from Iyyar to Elul, why? Is it related to the standardisation of the Hebrew Calendar?