1,332. Will the Moon be Visible?
Hilchos Kiddush HaChodesh 17:12
Next, go see in which constellation the third longitude falls. If it is in Pisces or Aries, add one-sixth of its value to the third longitude. If it’s in Aquarius or Taurus, add one-fifth. If it’s in Capricorn or Gemini, add one-sixth. If it’s in Sagittarius or Cancer, leave the third longitude alone, neither adding nor subtracting. If it’s in Scorpio or Leo, subtract one-fifth of the third longitude’s value. If it’s in Libra or Virgo, subtract one-third. The result of these operations to the third longitude, or from leaving it alone, is called the fourth longitude. Now go back to the first latitude and take two-thirds of its value. This is called the correction of the latitude. Determine if the moon’s latitude is to the north. If it is, add the correction of the latitude to the fourth longitude; if the moon’s latitude is to the south, subtract the correction from the fourth longitude. The result of these operations to the fourth longitude is called the arc of visibility.
Hilchos Kiddush HaChodesh 17:13
Now let’s try to see if the moon will be visible on Friday night, 2 Iyar of the (Rambam’s) current year. First, determine the sun’s actual location, the moon’s actual location and the moon's latitude for desired year (sic - apparently “time” is correct) using the methods we have discussed. You will find that the sun’s actual location is 7 degrees, 9 minutes in Taurus (7, 9). The moon’s actual location is 18 degrees, 36 minutes in Taurus (18, 36). The moon's latitude is 3 degrees, 53 minutes (3, 53) and it is to the south. This is our first latitude.
Next, subtract the location of the sun from that of the moon, which gives us 11 degrees, 27 minutes (11, 27). This is our first longitude.
Since the moon is in Taurus, the visibility difference for the longitude is one degree. Subtract this from the first longitude and we get a second longitude of 10 degrees, 27 minutes (10, 27). The latitude’s visibility difference is 10 minutes. Since the moon's latitude is to the south, the 10-minute visibility difference is added to the moon's latitude, which gives us a second latitude of 4 degrees, 3 minutes (4,3). Since the moon is in the 18th minute of Taurus, take one-quarter of the second latitude for the moon’s circuit. Therefore, at the desired time, the circuit will be one degree, one minute. The seconds don’t matter.