How to Stare at the Sun (Without Frying Your Retinas)

Humans aren't supposed to stare into the sun?the unfiltered UV rays will make your corneas burn and crack almost immediately, and overstimulation of the light-sensing cells in the retina can cause permanent tissue damage. But that doesn't stop us from trying. Amateur astronomers produce dazzling sun pictures such as these recent shots that rival those from government satellites, and NASA spacecraft keep constant tabs on our star. So how do sun gazers enjoy the glow without going blind?

Expert Amateurs
Staring at the sun through unfiltered cameras will record only a glowing splotch. But anyone can view the sun in photographs?with the right kind of camera equipment.

Alan Friedman, a greeting card printer by day, is an avid astrophotographer by night. With a pretty simple setup, he's produced images that rival Hubble shots in terms of beauty.

Friedman starts with a standard telescope and a diagonal?an attachment that, with the use of a prism to reflect light at a specific angle, allows viewers to look perpendicular to the telescope, giving them views they'd otherwise have to crouch below the telescope to see. He then uses a high-speed, high-resolution webcam and a hydrogen alpha filter. The camera allows him to scan many frames and select the crispest one as his final photograph, and the filter allows him to look at the sun safely, as well as take better images of it. The filter has many layers of material that interfere with various wavelengths of light, leaving an image that only includes certain levels of light emitted by burning hydrogen. This wavelength is both safe for the human eye and perfect for taking detailed photos of the sun?a far cry from the white blob an unfiltered camera would record.

Hobbies such as astrophotography are pretty addicting, and Friedman has progressed to much more elaborate equipment. But you can get started right now with a homemade telescope, a good filter, and a webcam.

NASA Techniques
Scientists have been staring at the sun for centuries. Before the advent of advanced imaging techniques that let people look at the sun without hurting their eyes, people such as Galileo observed sunspots and other solar phenomena by gazing at the sun when it was on the horizon or covered by clouds. Today space telescopes not only keep a constant watch on the sun, but do so without having to account for any atmospheric interference.

The Solar Dynamics Observatory, launched in February 2011 and currently in orbit at 22,000 miles above Earth, is NASA's main heliocentric project. SDO contains three instruments, which together take photographs of the sun every 10 seconds. With 10 times the resolution of an HD television, the probe takes every shot in eight wavelengths of light. Other solar observation satellites, such as the Solar Terrestrial Relations Observatory and the Solar and Heliospheric Observatory, also take pictures of the sun in eight wavelengths simultaneously.

The sun emits light in all visible colors, but since our eyes combine them all for processing, we see the sun as being white or yellow. Since each wavelength of light represents a different temperature of burning gas, focusing on one instead of another can allow researchers to capture images of different layers of the sun. That's how they know what's going on inside. Focusing on yellow-green light shows the surface of the sun, which is about 10,000 degrees Fahrenheit, but looking at extreme ultraviolet light reveals atoms at around 11 million F?a temperature many solar flares reach, allowing NASA researchers to see and document them.

Pinhole Peaks
There's one occasion that turns even the most casual of astronomers into a regular Icarus: the solar eclipse.

On a normal day the sun's rays are so bright that evolutionary failsafes kick in if we try to stare too long. Blinking, eye watering, and pupil dilation keep your sensitive peepers safe. But during an eclipse, just enough visible light is blocked to trick your reflexes, and you're able to keep your eyes open. The harmful UV rays are still present, though, so you'll still get the sunburned corneas. And without the pain and blinking that unblocked sunlight produce, you're more likely to stare long enough to sustain permanent retina damage. That's why we're all warned not to look directly at a solar eclipse.

The easy fix is a pair of specially made sunglasses (most standard glasses won't block enough UV rays to be of any help) branded either for eclipses or welding, which work by blocking enough of the strongest wavelengths of light to save your eyeballs. You can also make a pinhole projector, which projects a shadow of the eclipse onto a piece of cardboard or the ground. It produces a reversed image when light passes through a hole and hits a flat surface. Pinhole projectors are useful for any sun-blocking phenomenon, such as last year's transit of Venus. On a normal day a pinhole projector will just show you a round sun, but if anything is passing in front of it, you'll get a great view?without roasting your eyes.

Source: http://www.popularmechanics.com/science/space/telescopes/how-to-stare-at-the-sun-15131008?src=rss

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