# How does this July 4th optical illusion work? **URL:** \ **Category:** Factual Questions\ **Created:** [July 5, 2014, 1:43am UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384 "2014-07-05T01:43:09Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [July 5, 2014, 1:43am UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/1 "2014-07-05T01:43:09Z")
Every time I watch fireworks, I’m struck by the fact that the explosions I see always appear as if they’re blowing outward, toward me. It never looks like we’re seeing one of those things from behind. Nothing ever seems to be receding into the distance. How can I understand this effect? How can I see it more “realistically”? (I’m not sure I want to, but I want to be _able_ to) It always seems as if the fireworks are set to show their thing, facing me (and everyone who’s sitting near me). How to explain this impression? ---
**Author:** ![running\_coach](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/running_coach/32/15836_2.png) [@running\_coach](https://boards.straightdope.com/u/running_coach)\ **Post date:** [July 5, 2014, 1:53am UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/2 "2014-07-05T01:53:09Z")
Actually, there are pieces moving towards and away from you. It just doesn’t seem to be the case because you’re far away relative to the size of the “bloom” and it’s up in the dark sky with no background to judge against. ---
**Author:** ![USCDiver](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/uscdiver/32/354_2.png) [@USCDiver](https://boards.straightdope.com/u/USCDiver)\ **Post date:** [July 5, 2014, 2:10am UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/3 "2014-07-05T02:10:06Z")
Here ya go, this is what it looks like to be in the middle of the explosions [![](https://img.youtube.com/vi/a9KZ3jgbbmI/maxresdefault.jpg "Fireworks filmed with a drone") ](https://www.youtube.com/watch?v=a9KZ3jgbbmI) ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [July 5, 2014, 2:30am UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/4 "2014-07-05T02:30:53Z")
It is not an illusion, the glowing sparks really are coming (more or less) towards you. Some will be blown the other way too, but it is behind what is coming your way, so you don’t notice it so much. Also, the sparks are falling _downwards_, and you are down below where the rocket burst, so, again, they _are_ coming towards you. Most of the motion you see is falling, only a small part comes from momentum from the relatively feeble explosion by which the sparks are distributed. ---
**Author:** ![jtur88](https://avatars.discourse-cdn.com/v4/letter/j/e9c0ed/32.png) [@jtur88](https://boards.straightdope.com/u/jtur88)\ **Post date:** [July 5, 2014, 2:32am UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/5 "2014-07-05T02:32:09Z")
Your eye tells you that it is moving toward you because it is getting larger, like a truck approaching in the other lane on the highway… ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [July 5, 2014, 4:42am UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/6 "2014-07-05T04:42:53Z")
In combat, you don’t want to see it like it is in the video. ---
**Author:** ![Ornery\_Bob](https://avatars.discourse-cdn.com/v4/letter/o/da6949/32.png) [@Ornery\_Bob](https://boards.straightdope.com/u/Ornery_Bob)\ **Post date:** [July 5, 2014, 6:52am UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/7 "2014-07-05T06:52:18Z")
What jtur88 said. ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [July 5, 2014, 8:42am UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/8 "2014-07-05T08:42:44Z")
> [@Ornery\_Bob](#): > > What jtur88 said. No, it isn’t that at all. If it were, it would appear that the explosion as a whole is coming towards you, including the central point from which it originates. That is not how firework explosions look at all. It looks as though the individual sparks are coming towards you, and they look like that because most of them actually _are_ coming towards you. ---
**Author:** ![Novelty\_Bobble](https://avatars.discourse-cdn.com/v4/letter/n/a3d4f5/32.png) [@Novelty\_Bobble](https://boards.straightdope.com/u/Novelty_Bobble)\ **Post date:** [July 5, 2014, 9:39am UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/9 "2014-07-05T09:39:15Z")
I’m confused. When I see fireworks explode it looks to me like some of it is coming towards me, some of it is going away. That is what is happening after all. I’m looking at an expanding ball of sparkly glittery stuff. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [July 5, 2014, 11:33am UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/10 "2014-07-05T11:33:06Z")
Yeah. Maybe I’m missing something here, but a firework explosion is a big expanding sphere. No matter where you are, it IS coming towards you. There’s no “behind” to be at. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [July 5, 2014, 12:30pm UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/11 "2014-07-05T12:30:56Z")
It seems as if there should be some sense that 1/2 of the sphere, more or less, is moving away from you - from the center of the explosion. But all of the pieces seem to come outward toward the viewer. This is an illusion, of course, as several posters have said, since the whole of the thing is moving outward from the center. What is it about the circumstances that cause the bright pieces that actually are moving away from you to seem as if they’re part of the bunch that’s moving toward you? There is some aspect that tricks our perception, that no one here has pointed to yet, and I’m curious as to what that might be. ---
**Author:** ![pulykamell](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pulykamell/32/3166_2.png) [@pulykamell](https://boards.straightdope.com/u/pulykamell)\ **Post date:** [July 5, 2014, 1:52pm UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/12 "2014-07-05T13:52:10Z")
> [@Novelty\_Bobble](#): > > I’m confused. > When I see fireworks explode it looks to me like some of it is coming towards me, some of it is going away. That is what is happening after all. I’m looking at an expanding ball of sparkly glittery stuff. Yeah, to me it looks like a ball expanding, so parts are coming towards me, some away, some perpendicular, etc. I suppose it feels like it’s coming towards me in the sense that it’s coming down, but it doesn’t really feel like the whole three-dimensional mass is coming towards me (unless the winds are blowing in such a direction.) ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [July 5, 2014, 3:32pm UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/13 "2014-07-05T15:32:22Z")
> [@CC](#): > > It seems as if there should be some sense that 1/2 of the sphere, more or less, is moving away from you - from the center of the explosion. But all of the pieces seem to come outward toward the viewer. This is an illusion, of course, as several posters have said, since the whole of the thing is moving outward from the center. There may be some initial upward movement of some of the sparks, but pretty soon they come under the influence of gravity and start moving down, like the rest, and thus towards you (more or less). It is no illusion. I believe, in fact, that many of the charges are shaped so that very few, if any of the glowing sparks go upwards, but rather outwards, sideways, in a ring rather than a sphere, to produce the largest most spectacular display possible with a given amount of material. Of course, as they go outwards they also immediately begin to fall downwards, towards you. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [July 5, 2014, 4:35pm UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/14 "2014-07-05T16:35:10Z")
Unless I experience fireworks in a unique way, there is definitely an illusion of the fireworks exploding outward toward the viewer. That no one here acknowledges it doesn’t mean that it is not real. (Absence of evidence is not evidence of absence). I’ll keep looking. Thanks, Dopers. ---
**Author:** ![RaftPeople](https://avatars.discourse-cdn.com/v4/letter/r/6f9a4e/32.png) [@RaftPeople](https://boards.straightdope.com/u/RaftPeople)\ **Post date:** [July 5, 2014, 4:40pm UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/15 "2014-07-05T16:40:17Z")
> [@njtt](#): > > I believe, in fact, that many of the charges are shaped so that very few, if any of the glowing sparks go upwards, This is incorrect. 1 - Watch the video linked above 2 - If that were true then why do fireworks look the same whether you are 100 yards or 10 miles away? Just last night I watched 2 different shows, one was 1 mile away and I was almost level with explosions, the other was 10 miles away and I was also almost level with explosions (up on a hill), both looked the same. ---
**Author:** ![RaftPeople](https://avatars.discourse-cdn.com/v4/letter/r/6f9a4e/32.png) [@RaftPeople](https://boards.straightdope.com/u/RaftPeople)\ **Post date:** [July 5, 2014, 4:44pm UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/16 "2014-07-05T16:44:27Z")
> [@CC](#): > > Unless I experience fireworks in a unique way, there is definitely an illusion of the fireworks exploding outward toward the viewer. That no one here acknowledges it doesn’t mean that it is not real. (Absence of evidence is not evidence of absence). I’ll keep looking. Thanks, Dopers. A possibility is the following: The pieces that are moving away will be visually contained within the inner portion of the circle of explosion you are seeing due to angles etc. So some percentage of the pieces in the interior that appear to be slower moving and filling up space on this side are really on the other side and moving at the same rate as everything else. ---
**Author:** ![RaftPeople](https://avatars.discourse-cdn.com/v4/letter/r/6f9a4e/32.png) [@RaftPeople](https://boards.straightdope.com/u/RaftPeople)\ **Post date:** [July 5, 2014, 4:52pm UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/17 "2014-07-05T16:52:52Z")
```auto * * * * A F * G * B E * H * C D * * * * ``` In the above firework, the asterisks are pieces that are moving in a plane perpendicular to the viewer and A through H are moving towards and away from the viewer at various angles. But there is nothing visually to tell you whether a piece is moving towards or away from you, it’s just a bright light, so it looks like it’s all moving towards you. “E” could be moving directly towards you or directly away and because of that it stays in the center of the circle. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [July 5, 2014, 5:47pm UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/18 "2014-07-05T17:47:15Z")
> [@RaftPeople](#): > > ```auto > > > * * > * * > A F > * G * > B E > * H * > C D > * * > * * > > > ``` > > In the above firework, the asterisks are pieces that are moving in a plane perpendicular to the viewer and A through H are moving towards and away from the viewer at various angles. \*\* But there is nothing visually to tell you whether a piece is moving towards or away from you, it’s just a bright light, so it looks like it’s all moving towards you.\*\* > > “E” could be moving directly towards you or directly away and because of that it stays in the center of the circle. But that’s exactly my question. WHY should points A-H look like “it’s all moving towards you,” if some are moving away from you? ---
**Author:** ![RaftPeople](https://avatars.discourse-cdn.com/v4/letter/r/6f9a4e/32.png) [@RaftPeople](https://boards.straightdope.com/u/RaftPeople)\ **Post date:** [July 5, 2014, 6:32pm UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/19 "2014-07-05T18:32:05Z")
> [@CC](#): > > But that’s exactly my question. WHY should points A-H look like “it’s all moving towards you,” if some are moving away from you? Consider one single point of light from a firework that is moving away from you, do you think there is enough information for you to determine it is moving away? My guess is that it’s not easy to tell, it’s just a bright light moving to some degree in the plane perpendicular to you, and that the movement towards or away is much harder to detect. I think your brain assumes all are moving towards you because the entire thing is getting bigger, but it can’t really tell whether each individual one is moving towards or away. ---
**Author:** ![RaftPeople](https://avatars.discourse-cdn.com/v4/letter/r/6f9a4e/32.png) [@RaftPeople](https://boards.straightdope.com/u/RaftPeople)\ **Post date:** [July 5, 2014, 6:38pm UTC](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384/20 "2014-07-05T18:38:20Z")
If you watch the tail end of fireworks on youtube (after the initial explosion as pieces begin to curve towards the ground), you can see that lights that are at the same level and approximate same arc move at different speeds towards the ground, which implies that one is moving towards you and one is moving away because gravity is the same for both. Unless you look closely and analyze it, the ones moving away look just like the ones moving closer. [Next page](https://boards.straightdope.com/t/how-does-this-july-4th-optical-illusion-work/692384.md?page=2)