I am brand new to electronics and built this from scratch to better understand capacitors and transistors. With the switch left, the positive 9V charge charges C1 very rapidly with no resistor in the way. Charge cannot reach the LED though, because there is no charge on the base of Q1. After flipping the switch, C1 begins discharging more slowly than it charged because of R1 and a higher RC time. With a charge on the base of Q1, enough current flows through Q1 to light the LED. As the capacitor discharges, voltage on the Q1 base drops causing declining amperage to and dimming of the LED.
