Can a Solar Eclipse Really Blind You?


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Can a Solar Eclipse Really Blind You?

A tourist watches a solar eclipse through eclipse-viewing glasses in 2009 in Varanasi, India.

Credit: Pete Niesen / Shutterstock.com

People across the United States will have the chance to see a total solar eclipse on Aug. 21, the first time the spectacle was viewable from the continental U.S. since 1979. While it may be tempting to brush off warnings about looking up at this eclipse bare-eyed, don’t: The light of an eclipse really can damage your eyes — though warnings of total blindness may be overstated.

The condition is called solar retinopathy, and it occurs when bright light from the sun floods the retina on the back of the eyeball. The retina is home to the light-sensing cells that make vision possible. When they’re over-stimulated by sunlight, they release a flood of communication chemicals that can damage the retina. This damage is often painless, so people don’t realize what they’re doing to their vision.

Solar retinopathy can be caused by staring at the sun (regardless of its phase), but few people can stand to look directly at our nearest star for very long without pain. It does happen occasionally — medical journals record cases in which people high on drugs have stared at the sun for long periods of time, causing serious damage. Adherents of sun-worshipping religious sects are also victims. In 1988, for example, Italian ophthalmologists treated 66 people for solar retinopathy after a sun-staring ritual. [Gallery: Our Amazing Sun]

But during a solar eclipse, more people are at risk. With the sun almost covered, it’s comfortable to stare, and protective reflexes like blinking and pupil contraction are a lot less likely to kick in than on a normal day. Even pets are vulnerable to eye damage from looking at an eclipse, though they don’t tend to look directly at the sun. Even so, if they’re with you during your eclipse outing, your furry friends should wear protective glasses as well.

Early observers of astronomy sometimes found out about solar retinopathy the hard way. Thomas Harriot, who observed sunspots in 1610 but did not publish his discovery, wrote in 1612 that after viewing the sun his “sight was dim for an hour.” Oxford astronomer John Greaves was once quoted as saying that after sun observations, he saw afterimages that looked like a flock of crows in his vision. In the most famous case of all, Isaac Newton tried looking at the sun in a mirror, essentially blinding himself for three days and experiencing afterimages for months.

Scientists don’t have a good bead on the prevalence of eye damage after a solar eclipse. In one study, conducted in 1999 after a solar eclipse visible in Europe, 45 patients with possible solar retinopathy showed up at an eye clinic in Leicester in the United Kingdom after viewing the eclipse. Forty were confirmed to have some sort of damage or symptoms of damage; five of those had visible changes in their retina.

Twenty of the patients reported eye pain, while another 20 reported problems with vision. Of the latter group, 12 reported that their sight had returned to normal seven months later, but four could still see the ghosts of the damage in their visual field, such as a crescent-shaped spot visible in dim light. [If the Sun Is 93 Million Miles Away, Why Can’t We Look Directly at It?]

“Our series demonstrates that, contrary to popular belief, the majority of people with eclipse retinopathy are not totally blinded,” the researchers wrote in 2001 in the journal The Lancet. However, they warned, earlier post-eclipse studies had turned up more severe problems in patients, suggesting that widespread media warnings not to look at the eclipsing sun may have prevented more damage during recent eclipses.

Research also suggests that while a lot of the damage may heal, some may be permanent. One 1995 study followed 58 patients who sustained eye damage after viewing a 1976 eclipse in Turkey. Healing occurred during the first month after the eclipse, the researchers reported in the journal Graefe’s Archive for Clinical and Experimental Ophthalmology, but by 18 months, whatever damage remained was permanent up to 15 years later.

So, while it might be tough to go totally blind by looking at an eclipse, doing so without proper protection could leave a long-lasting stain on your vision. The only safe way to view an eclipse, according to NASA, is to use specially designed sun filters, often available at telescope stores, or to wear No. 14 welder’s glasses, available at welding specialty stores. Pinhole viewers — essentially a hole in a piece of cardboard or paper — can also be used to view the eclipse indirectly by casting a shadow of the sun on the ground or on a screen. [How to Build a Solar Eclipse Viewer: Photos]

REMEMBER: Looking directly at the sun, even when it is partially covered by the moon, can cause serious eye damage or blindness. NEVER look at a partial solar eclipse without proper eye protection. Our sister site Space.com has a complete guide for how to view an eclipse safely.

Editor’s Note: This article was first published in 2012 and updated for the Great American Eclipse in 2017.

Originally published on Live Science.

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NASA’s Total Solar Eclipse Maps Show Best Viewing Spots (Photos)


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NASA’s Total Solar Eclipse Maps Show Best Viewing Spots (Photos)

Path of a solar eclipse

Credit: NASA

A Sonic Attack in Cuba? How an Acoustic Weapon Might Work


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A Sonic Attack in Cuba? How an Acoustic Weapon Might Work

Credit: Shutterstock

A supersecret sonic weapon being used to attack diplomats in a foreign country may sound like the start of a sci-fi novel, but that’s exactly what several U.S. diplomats in Cuba may have been exposed to, the U.S. State Department recently announced.

The physical symptoms, which the State Department would not confirm, but which some news reports have suggested included hearing loss, got so bad that some of these officials had to be recalled from their duties in Havana.

“Some U.S. government personnel who were working at our embassy in Havana, Cuba, on official duties — so they were there working on behalf of the U.S. embassy there — they’ve reported some incidents which have caused a variety of physical symptoms,” Heather Nauert, a spokeswoman for the State Department, said in a news briefing Aug. 9.

After an extensive investigation, U.S. officials determined that a secret sonic weapon was to blame. [Mind Controlled Cats?? 6 Incredible Spy Technologies]

But what exactly could that weapon be, and how could it cause hearing loss without any of the people involved noticing a painful audible sound?

While the mysterious story has a lot of holes, one possibility is that the workers were exposed to infrasound, or low-frequency sound waves that are below the audible hearing range, said Charles Liberman, a hearing loss researcher at Harvard Medical School and Massachusetts Eye and Ear in Boston.

The strange symptoms emerged in the fall of 2016, when several employees at the U.S. embassy in Havana began complaining of physical symptoms. Many of the individuals were new to the embassy and some had to return to the United States because of the severity of their symptoms — the details of which have yet to be disclosed. An investigation by the U.S. government concluded that the symptoms could be attributed to a device that operated outside the audible hearing range and was used somewhere, possibly in their houses, Time magazine reported. Right now, there’s no word on whether these devices were deliberately used. [Flying Saucers to Mind Control: 22 Declassified Military & CIA Secrets]

In retaliation, the U.S. government expelled two Cuban diplomats on May 23, Nauert said.

Cuba denied any involvement in the bizarre scenario.

“Cuba has never permitted, nor will permit, that Cuban territory be used for any action against accredited diplomatic officials or their families, with no exception,” according to a statement from the Cuban government.

Another possibility is that some other hostile group (such as Russian agents) may have initiated the attack, Time reported.

There are so many details missing in this story that it’s hard to explain exactly what the device could be, Liberman said. However, sound-induced hearing loss requires that the mechanical part of the ear that senses audible sound be overloaded.

“You overstimulate the part of the ear that’s mechanically tuned to those frequencies and it falls apart,” Liberman.

If the people in the embassy didn’t hear anything, that suggests the weapon probably didn’t operate in the normal hearing range, or else it would have caused pain and been distracting, Liberman said. (Human audible hearing range is typically between 20 hertz, or cycles per second, and 20 kilohertz). If so, there’s little possibility for it to damage the mechanical parts of the ear that are tuned to those frequencies, he said.

However, it’s possible the devices somehow generate infrasound — the type of low-frequency sound given off by windmills or wind generators with the beating of the blades. Infrasound is below the human hearing range.

And yet, many people claim these machines are making them sick, and there are several lawsuits from people who live or work near wind farms, claiming they make them sick, according to Liberman.

“There is a growing controversy about people who live near these windmills who start feeling bad,” Liberman told Live Science. “They get headaches, they get dizzy, they get nausea.” [10 Odd Causes of Headaches]

For instance, a 2014 study in the journal Royal Society Open Science found that low-frequency sounds below the audible range could disrupt little whistles made by the ear, called spontaneous optoacoustic emissions, in response to noise. (How that mapped to symptoms, however, wasn’t clear.)

In this instance, one possibility is that the infrasound stimulated the part of the ear not dedicated to hearing — the vestibular system that controls balance, Liberman said. In that instance, the symptoms wouldn’t appear immediately.

“You could imagine them being very slow onset and very persistent,” Liberman said. “It might take days before you even notice any funny sensations.”

That may explain why the State Department refused to describe the symptoms experienced by their employees as including hearing loss, Liberman said.

The other type of sound humans can’t hear is ultrasound, which is above 20 khz. That’s a less likely possibility because high-frequency sound dissipates quickly with distance and in tissue such as the ear. However, high-intensity, focused ultrasound has been used for everything from breaking kidney stones to cauterizing tissues in the body.

But the fact that it doesn’t work well across long distances means it’s tough to imagine a device could get close enough to the people to work, without them suspecting, Liberman said.

What’s more, if a covert acoustic device using ultrasound produced enough energy to permeate and damage the ear from far away, it would probably heat the head up, too, Liberman said.

However, it’s theoretically possible that high-frequency ultrasound may have somehow damaged the blood vessels in the ear canal, thereby leading to damage, he said. That seems less likely, but “I’ve been in science long enough to not discount as impossible things that seem improbable,” Liberman said.

While the idea of a silent sonic weapon sounds like something out of James Bond, Inspector Gadget or the reject pile of DARPA, the idea of using sound as a weapon has a long history.

For instance, studies show that animals exposed to high-intensity, focused ultrasound can experience lung and brain damage. And a cruise line circling the pirate-infested waters off the Somali coast has taken to using a military-grade “sonic weapon” to deter would-be hijackers, the BBC reported. This long-range device, also known as a sound cannon, can cause permanent hearing loss at distances of up to 984 feet (300 meters), according to the BBC. Other companies have developed a magnetic acoustic device, commonly referred to as a sound laser, that deploys incredibly painful, focused beams of sound to deter people from an area,NPR reported. The Israeli army has also used a device known as “The Scream,” which damages the inner ear, causing nausea and dizziness,Wired reported.

Originally published on Live Science.

What is an MRI (Magnetic Resonance Imaging)?


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What is an MRI (Magnetic Resonance Imaging)?

MRIs are medical imaging systems used to diagnose health conditions.

Credit: MRI scan via Shutterstock

Magnetic resonance imaging (MRI), also known as nuclear magnetic resonance imaging, is a scanning technique for creating detailed images of the human body.

The scan uses a strong magnetic field and radio waves to generate images of parts of the body that can’t be seen as well with X-rays, CT scans or ultrasound. For example, it can help doctors to see inside joints, cartilage, ligaments, muscles and tendons, which makes it helpful for detecting various sports injuries.

MRI is also used to examine internal body structures and diagnose a variety of disorders, such as strokes, tumors, aneurysms, spinal cord injuries, multiple sclerosis and eye or inner ear problems, according to the Mayo Clinic. It is also widely used in research to measure brain structure and function, among other things.

“What makes MRI so powerful is, you have really exquisite soft tissue, and anatomic, detail,” said Dr. Christopher Filippi, a diagnostic radiologist at North Shore University Hospital, Manhasset, New York. The biggest benefit of MRI compared with other imaging techniques (such as CT scans and x-rays) is, there’s no risk of being exposed to radiation, Filippi told Live Science.

During an MRI, a person will be asked to lie on a movable table that will slide into a doughnut-shaped opening of the machine to scan a specific portion of your body. The machine itself will generate a strong magnetic field around the person and radio waves will be directed at the body, according to the Mayo Clinic.

A person will not feel the magnetic field or radio waves, so the procedure itself is painless. However, there may be a lot of loud thumping or tapping noises during the scan (it may sound like a sledgehammer!), so people are often given headphones to listen to music or earplugs to help block the sound. A technician may also give instructions to you during the test.

Some people may be given a contrast solution by intravenous, a liquid dye that can highlight specific problems that might not show up otherwise on the scan.

Young children as well as people who feel claustrophobic in enclosed places may be given sedating medication to help them relax or fall asleep during the scan because it is important to stay as still as possible to get clear images. Movement can blur the images.

Some hospitals might have an open MRI machine that is open on the sides rather than the tunnel-like tube found in a traditional machine. This may be a helpful alternative for people who feel afraid of confined spaces.

The scan itself may take 30 to 60 minutes, on average, according to the American Academy of Family Physicians.

A radiologist will look at the images and send a report to your doctor with your test results.

The human body is mostly water. Water molecules (H2O) contain hydrogen nuclei (protons), which become aligned in a magnetic field. An MRI scanner applies a very strong magnetic field (about 0.2 to 3 teslas, or roughly a thousand times the strength of a typical fridge magnet), which aligns the proton “spins.”

The scanner also produces a radio frequency current that creates a varying magnetic field. The protons absorb the energy from the magnetic field and flip their spins. When the field is turned off, the protons gradually return to their normal spin, a process called precession. The return process produces a radio signal that can be measured by receivers in the scanner and made into an image, Filippi explained.

An MRI scan reveals the gross anatomical structure of the human brain.

An MRI scan reveals the gross anatomical structure of the human brain.

Credit: Courtesy FONAR Corporation

Protons in different body tissues return to their normal spins at different rates, so the scanner can distinguish among various types of tissue. The scanner settings can be adjusted to produce contrasts between different body tissues. Additional magnetic fields are used to produce 3-dimensional images that may be viewed from different angles. There are many forms of MRI, but diffusion MRI and functional MRI (fMRI) are two of the most common.

This form of MRI measures how water molecules diffuse through body tissues. Certain disease processes — such as a stroke or tumor — can restrict this diffusion, so this method is often used to diagnose them, Filippi said. Diffusion MRI has only been around for about 15 to 20 years, he added.

In addition to structural imaging, MRI can also be used to visualize functional activity in the brain. Functional MRI, or fMRI, measures changes in blood flow to different parts of the brain.

It is used to observe brain structures and to determine which parts of the brain are handling critical functions. Functional MRI may also be used to evaluate damage from a head injury or Alzheimer’s disease. fMRI has been especially useful in neuroscience — “It has really revolutionized how we study the brain,” Filippi told Live Science.

Unlike other imaging forms like X-rays or CT scans, MRI doesn’t use ionizing radiation. MRI is increasingly being used to image fetuses during pregnancy, and no adverse effects on the fetus have been demonstrated, Filippi said.

Still, the procedure can have risks, and medical societies don’t recommend using MRI as the first stage of diagnosis.

Because MRI uses strong magnets, any kind of metal implant, such as a pacemaker, artificial joints, artificial heart valves, cochlear implants or metal plates, screws or rods, pose a hazard. The implant can move or heat up in the magnetic field.

Several patients with pacemakers who underwent MRI scans have died, patients should always be asked about any implants before getting scanned. Many implants today are “MR-safe,” however, Filippi said.

The constant flipping of magnetic fields can produce loud clicking or beeping noises, so ear protection is necessary during the scan.

Cari Nierenberg contributed to this article.