SELECT r_z___arcsecond__ FROM table_15318324_1 WHERE r_y___arcsecond__ = "−0.247"
Berapa banyak nilai r z (arcsecond) yang sesuai dengan nilai r y (arcsecond) −0.247?
CREATE TABLE table_15318324_1 (r_z___arcsecond__ VARCHAR, r_y___arcsecond__ VARCHAR)