I have a data frame called data, which has a column Dates like this,
                 Dates
0  2015-05-13 23:53:00
1  2015-05-13 23:53:00
2  2015-05-13 23:33:00
3  2015-05-13 23:30:00
4  2015-05-13 23:30:00
I know how to add a column to data frame, but how to divide Dates to 
          Day         Time
0  2015-05-13     23:53:00
1  2015-05-13     23:53:00
2  2015-05-13     23:33:00
3  2015-05-13     23:30:00
4  2015-05-13     23:30:00