John Pazmino
 NYSkies Astronomy Inc
 2011 August 21 initial 
 2015 September  12 current 

    It rained and rained during the NYSkies Seminar on August 19th, 
2011. The rain let up before we went for supper but clouds still 
covered the sky as we parted ways for home. 
     Recall that the Seminar on August 19th was a discussion of 
astrolabes, On the way home I had with me a couple show-&-tell 
astrolabes, including my own home-built wood model. That I built, with 
my father's assistance, in summer 1959  and saw its first astronomy 
service at the october 1959 solar eclipse. 
    It was still cloudy in Brooklyn when I got out from the subway and 
waited for my bus. While waiting, the sky started to clear. The clouds 
parted, letting the Moon shine thru. Just below the Moon was a bright 
    There is no star near the ecliptic bright enough to be so obvious 
as this one next to the Moon, It was no star; it was planet Jupiter. 
    I know, by seeing Jupiter earlier in the year, that the planet is 
in Aries about due south of Hamal (alpha Arietis). I did not see Hamal 
for the thin clouds over the Moon and the glare from street lights. 
    My bus arrived. I sat in a front seat to look out the windshield 
at the Moon. The bus for part of its route headed east, into the Moon. 
    The Moon and Jupiter, from familiarity with the local street 
layout, were almost at east, azimuth 80 degrees. Hamal, a little to 
the celestial north, would have been at azimuth 75 degrees. 
    Hmmm, what time was it while I was riding the bus to home? I could 
have looked at the time on my cell phone. Wait! This is a problem for 
the astrolabe! 
    What did I know? 

        Jupiter & Moon were south of Hamal. This star is far north 
    of the ecliptic. The Moon can not pass north of it. 
        I allowed  that all three were in the same ecliptic longitude. 
    This wasn't certain because the Moon moves rapidly to change her 
    longitude substantially within hours. 
        Because the Moon had to be just south of Hamal, maybe in 
    conjunction, I can pass up trying to mark Jupiter or Moon on the 
    rete of my astrolabe. I banked off of Hamal, which is plotted. 
        Hamal, being a bit north of the Moon, was in about azimuth 
    75 degrees. 
        I was in the New York latitude, north 40 degrees, that for 
which the astrolabe                                        was built. 
        The date was August 19th or maybe August 20th if after local 

    I pulled out my wood astrolabe, it being larger with bolder lines 
and markings. It was easier to read on the bumpy bus. I placed the 
regula over August 20 on the mean Sun scale and held it there with a 
paper-clip. August 20 was a labeled date, with no need of 
interpolation. The hour I finally determine would be close to the 0h 
of this date because when I was riding the bus it was already very 
late in the night of august 19th. 
    The astrolabe was now set for the date in mean solar time. If I 
set the Sun at its date along the ecliptic scale, the hour would be 
apparent solar time,  which wanders earlier and later than mean solar 
time during the year. 
    I then rotated the rete-&-regula together to put Hamal at azimuth 
75 degrees. As a quick check, the ecliptic, near Jupiter did sit at 80 
degree azimuth. The astrolabe was now set for both date and a known 
aspect of the stars. 
    The regula pointed to 22:40 on the hour scale of the mater. 
Because the regula was now tracking the Sun, this hour is also the 
mean solar time of the instant date. The hour of the observation was 
22:40 mean solar time, one hour andtwenty minutes before the midnight 
between the 19th and 20th. 
    Not quite.
    This hour is in standard time. In August we are in daylight 
savings time, one hour ahead of standard time. Astronomers ignore 
daylight time but for this exercise I did want to  prevailing clock 
hour.  I was heading home on my bus at 23:40 EDST on August 19th. 
   You do ask what other riders thought of this gadget, as much an 
dart board or game spinner. I explained to the lady next to me that 
it's a wireless tablet computer. That seemed to satisfy her curiosity.