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ArchaeoastronomyEquinox Observations at Atlatl RockValley of Fire State Park, NV, USA |
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My Visits to Atlatl Rock
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 List of all observations |
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2008, September 12 - first visit of the site: (~ 10 days before astronomical autumnal equinox)
 top of page2010, September 21 - second visit of the site to verify the assumed alignment. (~ one day before astronomical autumnal equinox)
top of page2011, June 24 - third visit of the site (three days after summer solstice)
top of page2015, September 22 to 25 - fourth visit of the site (around astronomical autumnal equinox) This time we were there four days around autumnal equinox and documented the path of the shadow from sunrise until all petroglyphs were in the shadow around 9 am PDT when the shadow tip had moved beyond the cross. I errorneously had assumed that at that time the shadow line would connect the centers of the markers to signal the equinox. This turned out to be wrong. Unfortunately the movement of the shadow line was not observed around noon. It is very probable that like in the observations from 2010 the markers stay always in shadow until the wall is in total self shadow. Camera: Canon IXUS 255 HS (2816 x 1880 pixel; time set to UT); time calibration: eight minutes have to be added to the time recorded in the data of the pictures! If times have been corrected, they are marked with "tc". Astronomical autumnal equinox: 2015-09-23-01:21 am PDT ;
top of page2017, September 17 to 21 - fifth visit of the site (observations all five days before astronomical autumnal equinox (September 22, 2017 at 01:02 pm PDT)) After the experience from the first three visits, this time each day pictures were taken about every 15 minutes. The pictures were taken always from the same point on the stairs starting at least at about 10 am PDT. The point on the stairs from where the pictures were taken was choosen in such a way that the cross was directly visible above one of the struts of the platform to be able to check the proper position. By this it was possible to create a movie from each day that showed the movement of the shadow at least in the two hours before the wall with the Atlatl petroglyphs was in total self shadow. The movies are shown here for each day together with the last picture taken on that day where the shadow edge was clearly defined. Camera: Canon IXUS 285 HS (5184 x 3888 pixel; time set to UT); time calibration (tc): no corretion necessary!
top of page2018, September 13 to 16 - sixth visit of the site (well before the astronomical autumnal equinox (September 22, 2018 at 06:54 pm PDT)) The 2017 observations started on September 17, five days prior to the astronomical autumnal equinox. As it turned out, this was almost too late to observe the shadow reaching the centers of the markes the last time before winter during the primary movement of the shadow shortly before the wall is in total self shadow. Therefore the 2018 observations started 9 days before the equinox to complete the time span with the four days before the 2017 observations had started. Thus, 9 days before astronomical autumnal equinox are now covered which should it make possible to determine the date when the shadow edge reaches the centers of the markers the last time. Like during the 2017 observations, each day pictures were taken about every 15 minutes from the same point on the stairs. Again, the resulting movies are shown here for each day together with the last picture taken on that day where the shadow edge was clearly defined. Camera: Canon IXUS 285 HS (3648 x 2432 pixel; time set to UT); time calibration: one minute has to be subtracted from the time recorded in the data of the pictures! If times have been corrected, they are marked with "tc".
top of page2023, March 24 to April 06 - seventh visit of the site (first observations in spring to verify the reverse order of events as compared to fall) From March 24 until April 6 2023 I documented the shadow at Atlatl Rock each day starting at about 9:00 am PDT until 12:30 pm PDT when the shadow on the petroglyphs was no longer visible as the whole area was in (self) shadow. It turned out, that the best defined shadow line (in Spring) occured at around 10:45 am PDT when the shadow was very stable and straight. This observations in spring that cover the time 4 days to 17 days after the spring equinox (which was on March 20, 2023 at 02:24 pm PDT) complement the observations made sofar only in fall and demonstrate perfectly the symmetry of events in spring and fall. The results have been collected on a separate page. top of page2023, September 17 to 22 - eighth and final visit of the site I documented the shadow at Atlatl Rock each day starting at about 9:00 am PDT until 12:30 pm PDT when the shadow on the petroglyphs was no longer visible as the whole area was in (self) shadow. This added 6 more days to the observations before fall eqinox. The last observation was only 0.5 days before equinox i.e. "on" the day of equinox, as close as none of the observations before. The six pictures taken at ~10:45 am PDT each day: 
 5d.5 before equinox 4d.5 before equinox 3d.5 before equinox 2d.5 before equinox 1d.5 before equinox 0d.5 before equinox Solar Quarter Day Overview of all fall 2023 observations: 
tc : Correction of the Clock Drift of the Camera The time of my camera always had been set to UT. Like almost each clock, this 
clock has a drift
that has to be taken into accout if it is ≥ 1 minute to calculate the proper coordinatesof the Sun (Az, El). If times quoted have been corrected, they are marked with "tc". |
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© 2024 Helmut Steinle
by Helmut Steinle