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At 52 degees North, the nominal declination South of which stars would not appear above the horizon is 38 degrees South, which is simple enough. But you will never actually see stars ON the horizon due to the light being absorbed by the atmosphere. A general rule of thumb is that stars are not visible until they are an altitude in degrees above the horizon equal to their magnitude. So, a 4th magnitude star would need to be 4 degrees above the horizon before it it seen. In consequence, a 4th magnitude star would need to have a declination North of 34 degrees South to be seen at latitude 52 degrees North.

Geoffrey Kolbe