A hammer candle is defined here as 1) the lower shadow (wick) is at least twice the length of the main body and 2) the close is in the top half of the range.
A shooting star has the opposite conditions 1) the upper shadow is at least twice the size of the main body and 2) the close is in the lower half of the range.
These candles should not be used by themselves but used in context ie with Bollinger bands, RSI or other oscillators they can form part of a mean reversion system.