EVENING PLANETS Saturn slips into the sunset’s glare after midmonth. The ringed world sets about an hour after sunset tonight. If you have a very good west-southwestern horizon, look for a star low above the treetops. That’s Saturn. By midmonth, Saturn sets about 30 minutes after sunset in bright twilight and is difficult to spot without binoculars. Mars crosses from Libra into Scorpius on Friday. On Oct. 10, Mars is the fourth star of the claws of the scorpion. Look to the southwest, as twilight fades, to spot a ruddy Mars just above Gamma Scorpii, or Dschubba. The next night, …