In Greek mythology, which of the seven Pleiades is the faintest of the stars?

In Greek mythology, Merope is one of the seven Pleiades, daughters of Atlas and Pleione. Pleione, their mother, is the daughter of Oceanus and Tethys and is the protector of sailors. Their transformation into the star cluster known as the Pleiades is the subject of various myths.

Merope is the faintest of the stars because she was the only of the Pleiades to have married a mortal. Her sisters had relations with gods and bore them sons, but Merope married Sisyphus and lived on the island Chios. Merope gave birth to Glaukos, Ornytion, Almus, Thersander and Sinon. The star Merope is often called the "lost Pleiad" because she was at first not seen by astronomers or charted like her sisters. One myth says that she hid her face in shame because she had an affair with a mortal man, another says she went to Hades with her husband, Sisyphus.