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With the right questions, and careful observation, a ghost story can transform from a spooky anecdote to a scientific experiment.

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Sources:
http://www.richardwiseman.com/resources/ghost-in-machine.pdf
http://doc.wind-watch.org/sources-effects-lfn-1996.pdf
https://www.wired.com/2009/10/scientifically-haunted-house/
http://gizmodo.com/some-ghosts-may-be-sound-waves-just-below-human-heari-1737065693
http://hyperphysics.phy-astr.gsu.edu/hbase/Sound/reson.html

http://www.news9.com/story/27445773/news-9-investigates-the-phenomenon-of-rods
http://www.amsky.com/ufos/rods/
http://www.straightdope.com/columns/read/1831/whats-up-with-rods-the-mysterious-insects-that-can-be-seen-only-on-video
http://www.skepdic.com/rods.html

https://web.archive.org/web/20070620170535/http://www.spsnational.org/wormhole/utd_sps_report.pdf
http://aapt.scitation.org/doi/abs/10.1119/1.3130609?journalCode=ajp,https://skeptoid.com/episodes/4038
https://www.livescience.com/37579-what-are-marfa-lights-texas.html

Image Links:
https://commons.wikimedia.org/wiki/File:Foil-IMG_1088-d-black.jpg
https://commons.wikimedia.org/wiki/File:Glasharfenspielerin.jpg
https://commons.wikimedia.org/wiki/File:Moths_attracted_by_floodlight.jpg
https://commons.wikimedia.org/wiki/File:E17_-_korte_sluitertijd.JPG
https://commons.wikimedia.org/wiki/File:E17_-_lange_sluitertijd.JPG
https://www.flickr.com/photos/texasbackroads/15366701103/in/photolist-qjo15m-q5f9n4-ppUmSt-84r3qi-4y3gKi-dgzxRM-dgzCqf-qnkSWt-egPY8t-wMVuA-6nyKTU-2moyNa-mz2NHp-q3MTGn-eEV6tc-8weJn3-6fbckn-Hkh7wt-TA5EfN-pp3PrG-pT9VBz-eF2cGd-eEV5Wt-eEV64n-5MD52f-eEV6Er-eEV5hZ-6ee7wt-eF2bBf-4y7VjU-eEV6zH-pBwmCY-eEV5Ec-eiRnwY-aitwhh-eF2ceW-ouiNXK-9hMjBF-6fbadc-ocP1m4-4y8vPW-4y4kzV-6ffjJJ-4y4m9t-q5gYeW-H3Me-4y8vgJ-YyF4wT-4y3GkR-nMuTsM/
https://www.flickr.com/photos/texasbackroads/15784149369/in/photolist-qnkSWt-egPY8t-wMVuA-6nyKTU-2moyNa-mz2NHp-q3MTGn-eEV6tc-8weJn3-6fbckn-Hkh7wt-TA5EfN-pp3PrG-pT9VBz-eF2cGd-eEV5Wt-eEV64n-5MD52f-eEV6Er-eEV5hZ-6ee7wt-eF2bBf-4y7VjU-eEV6zH-pBwmCY-eEV5Ec-eiRnwY-aitwhh-eF2ceW-ouiNXK-9hMjBF-6fbadc-ocP1m4-4y8vPW-4y4kzV-6ffjJJ-4y4m9t-q5gYeW-H3Me-4y8vgJ-YyF4wT-4y3GkR-nMuTsM-nMPohZ-4y7TRq-4y7UCu-4y4rsv-4y8s65-4y3rrM-4y3VJe/
https://commons.wikimedia.org/wiki/File:MirageAntarctique.jpg
From spooky ghosts to UFOs to mysterious, floating lights, there are all kinds of weird stories out there that seem impossible to explain unless there’s something paranormal going on.

But even the creepiest campfire stories can be debunked with the right questions and some careful observation. So here are three times scientists looked into something strange and found a perfectly rational — although in some cases, still very unsettling — scientific explanation for it.

Like in one supposedly-haunted lab in the UK. In the late 1990s, people who worked there could often feel waves of fear or shivers, and one engineer even saw a terrifying gray apparition from the corner of his eye. But he figured there had to be a reason for it.

This engineer also happened to be a fencer, and one day he brought his foil -- a thin fencing sword -- to the lab to adjust it for an upcoming competition. When he set the foil in a clamp, the blade started vibrating, almost like a ghost was shaking it. Except, it wasn’t a ghost.

By moving the foil around the lab and observing it, he figured out that the room contained a low-frequency sound wave, which he eventually traced back to the lab’s new fan. That explained pretty much all of the spooky stuff that had been going on. The foil shook because the sound wave was at its resonant frequency, a frequency that easily made it start vibrating.

All objects have one, and it’s also why if you run your finger around a glass, it'll sing a nice little song. This wave had a frequency of about 19 Hertz, or 19 vibrations per second, which is right below the range of human hearing — what’s called infrasound. Studies have shown that strong infrasound waves can cause uneasiness and dizziness, which can seem a lot like a haunting.

Because infrasound vibrates through your body’s tissues, it can affect your sense of balance, your breathing rate, and your blood pressure. It can even cause apparitions, since the resonant frequency of your eyeballs is also about 19 Hertz. So the ghost the engineer saw was caused by his eyeballs vibrating, which is super freaky, actually, and kind of gross to think about, but at least it wasn’t an actual ghost.

In some stories, something that’s said to be paranormal is caught on camera, too. The Internet is full of photos of long, rod-like insects with multiple sets of wings, and they’ve been passed off as things like UFOs, aliens, and interdimensional creatures. It turns out they’re just bugs -- usually moths.

The creation of these ghostly images has to do with how cameras work. Insects usually beat their wings a lot faster than a camera can capture an image so something like a moth will flap several times while a camera is recording one frame. And as it’s capturing that image, the insect is also moving across its field of view.

The result is that the moth looks like a blurry, elongated rod with multiple sets of wings. If you’ve ever tried to take a long exposure photograph of anything, you have probably seen something like this. The length of the rod is related to how fast the insect is moving and how far it is from the camera.

The faster and closer it flies, the longer your mysterious interdimensional visitor. Cryptozoologists call these "rods" or "skyfish" I like both of those names a lot, but as cool as they sound and as cool as it would be to have alien Interdimensional skyfish flying around us, these are just mostly moths flying to a different beat. Finally, if you’ve been to the tiny city of Marfa, Texas, you might’ve driven down US Highway 67 and spotted what looked like a UFO in the distance.

On some nights, these so-called Marfa Lights appear above the horizon, hovering and blinking like spaceships. There’s even a viewing area for them along the road. But surprise: They’re also not aliens.

Local university students thought they might be caused by car headlights, so in 2004, they did experiments to shed some light on the situation. They set up cameras to monitor the lights and a box to measure the traffic on Highway 67. They also tracked a car driving down the road to see if the highway was directly visible from the Marfa Lights viewing area.

The results weren’t that spooky or surprising: they found that the Marfa Lights were probably caused by the atmosphere reflecting headlights from the highway. There was a direct relationship between the number of Marfa Lights and the amount of traffic, and the group at the viewing area could even tell which lights corresponded to the car they were tracking. In 2008, these findings were supported by another team, who found that the lights could also come from streetlights or campfires.

You’d think it would be pretty easy to tell whether what you’re looking at is a pair of headlights or an alien spaceship, but the Marfa Lights are tricky because they don’t really look like headlights. They’re often magnified and kind of shimmer. That comes from a mirage, where light rays bend and displace an image.

Specifically, it’s caused by what’s known as a superior mirage, where an image appears above where it should be. It happens when a layer of warmer air sits on top of cooler air, which is the opposite of normal -- usually, the lower layers of the atmosphere are warmer because they’re heated by the Earth’s surface. Air at different temperatures has different densities, so it bends light at different angles.

When light rays pass through a temperature inversion, they can bend in a way that creates an image above where the object actually is. And to be clear, when it comes to the Marfa Lights, that object is just a car’s headlights on a lonely road. Not an alien spaceship.

There are plenty of other stories of the paranormal that are still unexplained — whether because they can’t be replicated, or there isn’t enough data about them to come to any conclusions. But sometimes, all you need are the right questions and a healthy dose of skepticism. Also, maybe a fencing foil.

Thanks for watching this episode of SciShow. If you want to learn more about debunking myths and bad science, check out our miniseries on Victorian pseudoscience. And to learn more every day with us, you can go to youtube.com/scishow and subscribe.