Neptune: Once Around . ... Credit Copyright: NASA , ESA , Hubble Heritage Team ( STScI / AURA ) Explanation: Neptune rotates once on its axis in about 16 hours. ... Because Neptune's axis of rotation is tilted to its orbital plane by 29 degrees, compared to Earth's 23.5 degrees, Neptune experiences seasons analogous to Earth's . As early summer comes to Neptune's southern hemisphere and winter to the north, Hubble observations have shown cloud activity shifting to the northern hemisphere. ...