Sum of Rows based on multiple variables

"I'm not sure that the title quite explains what I am looking for:

I have attached a file with sample data. I am trying to (without using a pivot table) find the number of rows (or sum up the number of stars seen) for each group by month.

The results that I am hoping to see are saved within the file as well (as the second data set). Please help if you can. Thank you. "