What is it when you hit the back of your head and then see sharp bright light out corner eye for about 30minutes?

This symptom is commonly known as "seeing stars" or "starbursts." It occurs when you experience a sudden, sharp impact to the head, such as hitting the back of your head. The medical term for this phenomenon is "phosphenes."

When you hit your head, the impact can cause the retina in your eyes to be stimulated, which sends signals to the brain. These signals are interpreted as flashes of light or star-like patterns. The phenomenon is usually temporary and should subside within a few minutes or hours.

In most cases, seeing stars after hitting your head is not a cause for concern and does not indicate any serious injury. However, if the symptoms persist for an extended period of time or are accompanied by other concerning symptoms, such as dizziness, nausea, or vomiting, it's important to seek medical attention to rule out any underlying injuries or conditions.