Wednesday, July 12, 2006

Practice Henge

Charlie, Kin, and I met up at 34th and Park for the second Manhattan-henge event of the year. Charlie had found two dates: 11 July from American Museum of Natural History and 12 July from Astronomy Picture of the Day (APOD). From the looks of this evening's turn out and that the Sun did not set between the buildings/street probably means that folks will turn out for it tonight on 12 July 2006. The hazy sky did not help but I thought that if the Sun did creep into that less-than-two-degree-corridor-between-the-buildings that it would be strong enough to punch through that crud. In fact, the haze could be a benefit to attenuate the Sun's brilliance for sharper photos and brief naked eye views.
While waiting, a few others showed up. John arrived with a video camera mounted on a monopod. He was going to shoot the event for a cable TV program. It turned out to be a practice run for him. A family of 3 showed up, as well. Dad had seen the Sun earlier in the day remarking that it was hardly seen. He was still optimistic that we might see something. Perhaps we'll see them again tonight. Although the event didn't happen the way we expected the meeting of this small group was just as enjoyable.

An empty intersection, looking south. Compare to this.

Back on 28 May, the last Henge event, the Sun set around azimuth 298°32'. This value was determined by using a value for the Sun's elevation at 0°28', and the angular size of the Sun is approximately 31'34".

On 11 July, at 8:20pm the Sun was 0°29' altitude with an azimuth of 299°09'. The Sun's angular size, according to Planetarium for the Palm, is 31'28".

On 12 July, at 8:20pm the Sun will be 0°25' altitude with an azimuth of 299°02'. The Sun's angular size remains unchanged at 31'28".
For both dates the ecliptic is almost 45°. Actually, May appears steeper with possibly a 60° incline as opposed to a 45° for July.

Given the azimuth values, the Sun will set slightly North, 30 arc minutes, which is nearly a solar diameter. From my point of view at 34th & Park, the street corridor is slightly less than my forefinger extended at arm's length. A finger width is estimated to be 2°. I haven't calibrated that measurement to be any more exact ;^D but my guess is that the angular measurement of the street to 1° 45'. That measurement yields a street corridor measurement in terms of solar diameters to be ~3 ½.
This evening we didn't even see a hint of the Sun but it should have passed through our field of view. Unless I missed something the Sun set south of the street opening. Weather conditions don't look promising for tonight but will probably go and check it out to see if a crowd turns out.