ssh-keyscan returns different values on each invocation

ssh-keyscan -H <<host address>> will return a different value each time it is invoked. the key type remains the same. the public key remains the same. but the first component differs. i had expected the first component to remain the same during each invocation. indeed, i had expected the entire value returned to remain the same during each invocation. i was hoping someone could explain this to me.