What time is it if Rigel is 25 degrees above the eastern horizon on January 29th?
Place Rigel at 25 degrees above the eastern horizon, halfway between the 20 and 30 degree almucantars. Now set the rule against the sun (i.e. the 10th degrees of Aquarius.) One can see that the rule points to 5:45 PM. It is interesting to note that the sun had not yet reached the astronomical twilight almucantar in this example. Thus, only the brighter stars are visible (fortunately, Rigel is one of the brightest.
