five o'clock
When she joined him a few minutes later in the deck-chamber the three-quarter disc of Jupiter was rapidly approaching the full . Its phases are invisible from the Earth owing to the enormous distance ; but from the deck of the _ Astronef _ they had been plainly visible for some days , and , since the huge planet turns on its axis in less than ten hours , or with more than twice the speed of the Earth 's rotation , the phases followed each other very rapidly . Thus at twelve o'clock noon by _ Astronef _ time they might have seen a gigantic rim of silver-blue overarching the whole vault of heaven in front of them . By five o'clock it would be a hemisphere , and by five minutes to ten the vast sphere would be once more shining full-orbed upon them . By eight o'clock next morning they would find Jupiter `` new '' again . They were now falling very rapidly towards the huge planet , and , since there is no up or down in Space , the nearer they got to it the more it appeared to sink below them and become , as it were , the floor of the Celestial Sphere . As the crescent approached the full they were able to examine the mysterious bands as human observers had never examined them before .