Candle clocks were used in the past to measure time at night or on cloudy days. Marks were placed on candles indicating hours, and as the candle burned down between marks, it indicated the passage of an hour. Disadvantages included not being able to precisely measure time if the candle was blown out before reaching a mark, and only being able to measure elapsed time rather than telling the exact time of day. The document also discusses how sunrise and sunset times change with the seasons, with days getting longer in summer and shorter in winter.