 From Jupiter 's surface — or rather , from just above its cloudtops — Amalthea would appear very bright , shining with a magnitude of − 4 @.@ 7 , similar to that of Venus from Earth . At only 8 arcminutes across , its disc would be barely discernible . Amalthea 's orbital period is only slightly longer than its parent planet 's day ( about 20 % in this case ) , which means it would cross Jupiter 's sky very slowly . The time between moonrise and moonset would be over 29 hours . 
