wHEN DID I GET HOME? ------------------ John Pazmino NYSkies Astronomy Inc firstname.lastname@example.org www.nyskies.org 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 star. 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 midnight. --------- 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.