Why can I not alias a column in a view? [duplicate]

Question

I am trying to create a view that provides all quarter starts from a date dimension. Here it is:

CREATE OR REPLACE VIEW quarter_starts AS
SELECT min(day_number_in_epoch) AS day_num FROM date_dimension dd
GROUP BY dd.calendar_year_quarter;

And postgres gives the error:

ERROR:  cannot change name of view column "min" to "day_num"