Electric light be made with a screw-thread base, two metal pins, two metal caps or a bayonet cap. The three main categories of electric lights are incandescent lamps, which produce light by a filament heated white-hot by electric current, gas-discharge lamps, which produce light by means of an electric arc through a gas, and LED lamps, which produce light by a flow of electrons across a band gap in a semiconductor. Before electric lighting became common in the early 20th century, people used candles, gas lights, oil lamps, and fires. Cornish chemist Humphry Davy developed the first incandescent light in 1802, followed
Gold Medal of the Royal Astronomical Society 1828. No other woman received the award until Vera Rubin in 1996. Margaret and Geoffrey Burbidge were jointly awarded the 2005 Gold Medal in astronomy, the first joint award since 1886. The medal features an image of the 40-foot telescope constructed by Sir William Herschel, the first President of the RAS. Gold Medal of the Royal Astronomical Society The Gold Medal of the Royal Astronomical Society (RAS) is the highest award given by the RAS. The RAS Council have "complete freedom as to the grounds on which it is awarded" and as such it can be awarded for any reason.