# What is this dark line in the Florida sky? **URL:** \ **Category:** Factual Questions\ **Created:** [August 3, 2013, 7:15pm UTC](https://boards.straightdope.com/t/what-is-this-dark-line-in-the-florida-sky/665267 "2013-08-03T19:15:51Z")\ **Posts on this page:** 6\ **Page:** 2
**Author:** ![JWT\_Kottekoe](https://avatars.discourse-cdn.com/v4/letter/j/3ec8ea/32.png) [@JWT\_Kottekoe](https://boards.straightdope.com/u/JWT_Kottekoe)\ **Post date:** [August 4, 2013, 4:33am UTC](https://boards.straightdope.com/t/what-is-this-dark-line-in-the-florida-sky/665267/21 "2013-08-04T04:33:58Z")
Thanks, Fubaya. Until I read your post, I was planning to link that same page, which I discovered several months ago after a friend told me about contrail shadows. ---
**Author:** ![moriah](https://avatars.discourse-cdn.com/v4/letter/m/b2d939/32.png) [@moriah](https://boards.straightdope.com/u/moriah)\ **Post date:** [August 4, 2013, 4:40am UTC](https://boards.straightdope.com/t/what-is-this-dark-line-in-the-florida-sky/665267/22 "2013-08-04T04:40:24Z")
> [@Fubaya](#): > > [Here](http://contrailscience.com/contrails-dark-lines-chemtrails/) is a site which might help explain it. Scroll down to number 3, the edge shadow or volumetric shadow. There’s even a video of similar shadows he took in his kitchen that should be familiar to everyone. We’ve all seen them, just not in the sky. Might explain it? That’s open and shut, thanks! ---
**Author:** ![cmyk](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmyk/32/3353_2.png) [@cmyk](https://boards.straightdope.com/u/cmyk)\ **Post date:** [August 5, 2013, 12:50am UTC](https://boards.straightdope.com/t/what-is-this-dark-line-in-the-florida-sky/665267/23 "2013-08-05T00:50:18Z")
> [@njtt](#): > > I am still not understanding how, if it is a shadow, it can be seen without being cast on something. The sky would be pitch black in broad daylight if the atmosphere didn’t absorb and scatter light (or if we didn’t have one). This is a common volumetric effect, and what we are seeing is the occlusion of sunrays through the thickness of the atmosphere. What we think of as typical shadows is only the planar projection/occlusion of this light onto another surface; say, your body casting a shadow on the sidewalk. However, if you were to fill the area with fog, you would see a similar occlusion of rays projecting from your body to form the cast shadow. In this picture, we’re seeing only the occlusion as projected through something opaque in the atmosphere—not what’s casting it, or any planar projection we commonly think of as a shadow. ---
**Author:** ![jtur88](https://avatars.discourse-cdn.com/v4/letter/j/e9c0ed/32.png) [@jtur88](https://boards.straightdope.com/u/jtur88)\ **Post date:** [August 5, 2013, 3:54am UTC](https://boards.straightdope.com/t/what-is-this-dark-line-in-the-florida-sky/665267/24 "2013-08-05T03:54:59Z")
Would a shadow of a contrail appear vertical, reaching the horizon? A contrail is horizontal, and would have to be long enough to reach the horizon in order to cast a shadow at the horizon, and the contrail would be visible there, too. A vertical shadow would require a vertical planar surface upon which to cast the shadow. ---
**Author:** ![Elendil\_s\_Heir](https://avatars.discourse-cdn.com/v4/letter/e/7cd45c/32.png) [@Elendil\_s\_Heir](https://boards.straightdope.com/u/Elendil_s_Heir)\ **Post date:** [August 5, 2013, 4:14am UTC](https://boards.straightdope.com/t/what-is-this-dark-line-in-the-florida-sky/665267/25 "2013-08-05T04:14:13Z")
> [@Mangetout](#): > > It looks like a crepuscular ray (or rather, a shadow) - I’ve seen pictures like that before, although with that many other clouds visible, there would normally be more rays. The first rule of crepuscular rays is we don’t talk about crepuscular rays. Sheesh. ---
**Author:** ![cmyk](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmyk/32/3353_2.png) [@cmyk](https://boards.straightdope.com/u/cmyk)\ **Post date:** [August 5, 2013, 6:21am UTC](https://boards.straightdope.com/t/what-is-this-dark-line-in-the-florida-sky/665267/26 "2013-08-05T06:21:57Z")
> [@jtur88](#): > > Would a shadow of a contrail appear vertical, reaching the horizon? A contrail is horizontal, and would have to be long enough to reach the horizon in order to cast a shadow at the horizon, and the contrail would be visible there, too. > > A vertical shadow would require a vertical planar surface upon which to cast the shadow. This all depends on angles and alignments. At just the right angle everything could alight to cast a column that appeared as a vertical shaft, keeping in mind these are the shafts of light occluded, and not the shadow projecton cast as if on some wall in the sky. [Previous page](https://boards.straightdope.com/t/what-is-this-dark-line-in-the-florida-sky/665267.md?page=1)