https://neildegrassetyson.com/letters/2001-09-12-the-horror-the-horror/

Excerpt from email sent the next day

When the first plane hit at 8:50, they evacuated the school without incident. I noticed WTC 1 on fire in a high floor upon returning from voting, about 8:55 AM. Large crowds of onlookers were gathering along the base of City Hall Park as countless fire engines, police cars, and ambulances screamed past.

I went home, grabbed my camcorder, went out to the street and started filming. I consider myself to be emotionally strong. What I bore witness to, however, was especially upsetting, with indelible images of horror that will not soon leave my mind.

  1. I first see WTC 1 on fire at a high floor. Not just flames coming out of some windows, but four or five entire floors on fire with smoke penetrating floors still higher.

Upsetting enough, but then…

  1. Among the papers and melted steel fragments fluttering to the ground, I notice that some debris was falling distinctly differently. These weren’t parts of the building that were falling. These were people, jumping from the windows, their bodies tumbling in rapid descent from the eightieth floor. I noticed about ten such falls, morbidly capturing three of them on tape.

Upsetting enough, but then…

  1. A fiery explosion burst forth from a corner of WTC 2 about two thirds of the way up, perhaps the 60th floor. The fireball created an intense radiative impulse of heat from which we all had to turn our heads. From my vantage point, I could not see the plane that caused it, which hit 180° on the other side of the building. Nor did I know at the time that a plane caused it. I first thought it was a bomb, but the explosion was not accompanied by the tell-tale acoustic shockwave that rattles windows. This was simply a low frequency rumble.

As it burst from the building’s corner, the fireball was so large that it extended all the way across to WTC 1. The fact the building’s corner exploded tells me that the ignited jet fuel got focused by the sides of the floor into which the second plane flew, meeting at the corner with increased explosive pressure. The flames were accompanied by countless thousands of sheets of paper that burst forth, fluttering to the ground as though every filing cabinet on multiple floors was emptied.

The fact that the second tower was now on fire made it clear to us all on the street that the first fire was no accident and that the WTC complex was under terrorist attack. Morbidly, I have the explosion on tape and the sounds from the horrified crowd surrounding me. At this point I stopped filming, and went back inside my apartment.

https://neildegrassetyson.com/photos/2001-09-11-world-trade-center-photos/