28 Tevet 5772
YOM KIPPUR KATAN
...The very end of a month, when the moon is barely visible, is an appropriate time to remind ourselves of what we are to be doing with our lives. We can gaze upwards and see almost none of the moon, knowing that a mere two weeks later, the moon will be full. Similarly, we can gaze within ourselves and see not even a tiny spark of inspiration or desire to strive for greatness. At the same time, we should know that we have the ability within us to shine brightly. Right before we begin a new month, we should inspire ourselves to improve, regardless of the method we employ to do. For this reason, specifically the day before Rosh Chodesh is set aside for a day of self improvement and introspection, thus earning it the name Yom Kippur Katan.
See also Jewish Virtual Library