The 9/11 Forum

It seems we need a closer look at the time of the "WTC7 explosion".
Let's do some calculation.

angle of Murray Street = 120.87°


some relations:


a = 118px
b = 339px
green angle = solar azimuth - Murray St angle

For all possible sun position that casts a shadow that reaches down to the sidewalk but don't cast a shadow on the sidewalk we can say:

SIN(green angle) = a/d
SIN(solar azimuth - Murray St angle) = a/d

ARCSIN(a/d) + Murray St angle = solar Azimuth
ARCTAN(b/d) = solar elevation

d is all we miss but we can say that

d min = a

For all possible d>a we get combinations of solar azimuths and elevations:


Now we just need to find out which combination fits any possible combination on 11th Sep. 2001!


The orange curve represents the way of the sun on 9/11 between 9:00am and 12:00am.
The blue curve represents all possible combinations of azimuth and elevation for a shadow that reaches down to the sidewalk but don't cast a shadow on the sidewalk.
The intersection of both curves is at 10:18am (but without Daylight saving time!!!).



Finally we should estimate the possible failure of the result.
May be the image from the video is somehow distorted or the perspective distorts the relation of a/b.
It's about 1px per minute for the length of a. In other words, if a would really be a=108px then we would get about 10:08am and for a=128px we would get 10:28am.
The green marquise has a special feature: a round corner. The viewing angle doesn't matter! We always see the right relation between the hight of the wall and the width/radius of the green marquise.

The Google Earth image shows the green marquise just 101px wide. For this relation we get a time between 10:00am-10:10am.

A later time than about 10:20am would require a much wider marquise than measured in both images but since the green squares below the marquise don't show any visible distortion a later time can be excluded.

There is another way to confirm the time. The video pans to the opposite side of the street. For a short moment a lens flare effect becomes visible that points directly at the position of the sun.

This frame...

...shows the facade. The left edge of the frame is approximately aligned with the corner of the building. The roof line is visible too.
The corner of the roof corresponds to a solar azimuth of about 150° and therefore a time of 10:40am. Furthermore we see that the vertical lines are bowed.

Obviously the video was shot using a wide angle optic that caused some pillow distortion. That distortion stretches the horizontal axis and shortens the vertical axis. Therefore the relation of wall height and the width of the marquise should also be distorted in that way.

If so then we get an earlier time than 10:18am.

The lens flare effect points at an azimuth of about 140° (about 10:10am).


Nevertheless, there is a major mistake in all these times because Manhattan had Daylight Saving Time.
That means it is 1 hour later already and about
11:10am EST.



What time is it?

It seems it's 11:11am.

10:18 a.m. to Collapse of WTC 1 at 10:28:22 a.m.
"By shortly after 10:18 a.m., the fire spreading toward the west on the north side of the 92nd floor was approaching the edge of the face. Despite the presence of flames over a significant length of the floor, the fire appeared to be burning with a low intensity at separated locations, with essentially no smoke coming from nearby open windows. An event took place within the tower at 10:18:48 a.m. that generated a pressure pulse with sufficient magnitude to force a large amount of smoke from the open windows on the 92nd floor, along with smaller amounts from open windows on other floors on the north face and on the other faces of the tower. While it seemed likely that the pressure pulse was generated by some sort of collapse within the tower, e.g., a portion of the core settling or a partial floor collapse, it has not been possible to determine the nature of the event or even its general location based on the visual record."
- NIST NCSTAR 1-5 p17

Now with the (partial) release of the NIST Cumulus video database, we have some more views of the event. WPIX chopper from West, CBS chopper from SW, Onno de Jong from NE, Craig Braden and others from North, and Main/Ballou from East.



(has some 4x speed) Additionally I took the videos and joined the 3 available 4:30 length clips for each video starting around 10:17 and running until after 10:28 ... adjusting to double speed.











Video release details/download: http://911datasets.org/index.php/Release_14_-_NIST_Cumulus_Video_Database

Sorry if all those videos seemed like spam At least they all show the pressure pulse.

More specifically, the Craig Braden video, (download avi) in the first few seconds, shows 10:18 am seconds before the pressure pulse, zoomed in on what appears to be a fire on that floor.

I watched Achimspok's video again - WTC1 Collapse South - dust - and came to the part where it said the pressure pulse started the fire. That appears to be wrong. But the rest of the video is great!