How to safely watch a solar eclipse

Schoolgirls eclipse
Schoolgirls eclipse

Some people have been willing to travel halfway round the world to see a solar eclipse. But for many in the United States, that won’t be necessary on August 21, 2017. They’ll only need to walk outside to gaze at a partial or full eclipse of the sun. However, to view such a spectacle safely, they will need to take some special steps.

People have “watched eclipses in all history,” says Jarita Holbrook, a fellow at the National Science Foundation in Washington, D.C. (This physicist usually works at the University of the Western Cape in Cape Town, South Africa.) Ancient people “knew that the moon was covering up the sun,” she says. And they made up myths to describe why this happened. Some described the sun and moon as fighting. Others talked about a marriage between the sun and moon.

But just gazing up at the sun is a bad idea. Its intense light can easily damage eyes. “You have to wear your protective glasses before totality — before the moon totally blocks the sun,” warns Shadia Habbal. She’s an astronomer at the University of Hawaii at Manoa. Once totality happens, you must put the glasses back on just before the moon moves to let light through again. And people watching a partial eclipse must keep their glasses on throughout the entire event.

The eyes have it

The sun’s electromagnetic energy includes several types of radiation. Some of that is visible light. It’s why you see the sun. But there’s also ultraviolet light. It has wavelengths shorter than those of visible light, close to violet on the spectrum. You can’t see this radiation, but it can cause sunburn, DNA damage and eye injury. The sun also emits infrared radiation. It has longer wavelengths than red light and transfers heat.

If someone looks directly at the sun, its energy can harm light-sensitive cells called rods and cones. They’re found on the retina at the back of the eye. Harm to those cells can happen without warning. That part of the eye has no pain cells.

“The primary danger is photochemical,” says Rick Fienberg. He’s an astronomer in Boston, Mass., with the American Astronomical Society. “Intense sunlight can cause chemical reactions to occur in the retina that damage or destroy the rods and cones.” That harm could lead to partial or total blindness. And such damage can be permanent.

“The light interacts with materials within the cell,” explains Ralph Chou. He’s a vision scientist at the University of Waterloo in Ontario, Canada. These reactions produce molecules such as peroxide (Puhr-OX-ide) and hydroxyl (Hy-DROX-uhl) radicals. Those chemicals can easily swipe electrons from nearby atoms or molecules. And resulting cell-killing free-radical reactions can “very rapidly chew up the internal organelles of the cell.” Organelles are parts of a cell that do specific jobs. Depending on the harm, damage to them can be either temporary or permanent.

eclipse Japan

It’s time to redefine what qualifies as a planet

PLANET OR NOT? A group of planetary scientists label Pluto and many other orbs in the solar system as planets, despite the definition set down by the International Astronomical Union in 2006.

Pluto is a planet. It always has been, and it always will be, says Will Grundy of Lowell Observatory in Flagstaff, Arizona. Now he just has to convince the world of that.

For centuries, the word planet meant “wanderer” and included the sun, the moon, Mercury, Venus, Mars, Jupiter and Saturn. Eventually the moon and sun were dropped from the definition, but Pluto was included, after its discovery in 1930. That idea of a planet as a rocky or gaseous body that orbited the sun stuck, all the way up until 2006.

Then, the International Astronomical Union narrowed the definition, describing a planet as any round object that orbits the sun and has moved any pesky neighbors out of its way, either by consuming them or flinging them off into space. Pluto failed to meet the last criterion (SN: 9/2/06, p. 149), so it was demoted to a dwarf planet.

Almost overnight, the solar system was down to eight planets. “The public took notice,” Grundy says. It latched onto the IAU’s definition — perhaps a bit prematurely. The definition has flaws, he and other planetary scientists argue. First, it discounts the thousands of…

A slowdown at the sun’s surface explained

The Sun
SOLAR SLOWDOWN The sun’s surface rotates more slowly than its inner layers. Scientists now have an explanation: Photons leaving the sun could carry angular momentum away, slowing the top layer’s spin.

Never underestimate the power of a little sunlight.

Light particles, or photons, emitted from the sun’s surface, could explain a long-standing solar mystery — why the sun’s outermost layers rotate more slowly than its core.

Because the sun isn’t a solid ball, regions at different depths or latitudes rotate at different rates. For decades, scientists have wondered why the outer 5 percent of the…