In the 1880s, Giovanni Schiaparelli mapped the planet more accurately, and suggested that Mercury's rotational period was 88 days, the same as its orbital period due to tidal locking.
I 1880'erne kortlagde Giovanni Schiaparelli planeten mere præcist og foreslog, at Merkurs omdrejningstid var 88 dage, det samme som dens omløbstid pga. tidevandslåsning.