If you’re in the right place, a couple of rare astronomical events in the coming weeks — an annular eclipse and a transit of Venus — may make it worthwhile to buy a pair of eclipse glasses.
Tokyo last experienced an annular eclipse — when the edge of the sun appears as a bright ring around the moon — 173 years ago, in September 1839. The next isn’t due for hundreds of years.
Weather permitting, residents of much of Japan, including Osaka, Nagoya and Tokyo, can treat themselves to the sight early on the morning of May 21.
Then, for a few hours on June 6, Venus will pass in front of the sun, another rare event Japan won’t see again until 2117.
Astronomers and space enthusiasts are excited about the uncommon events. Only those in Okinawa and the Ogasawara Islands were able see the last total eclipse, in July 2009. But this time, more than 80 million people will be able to view the annular eclipse, if the skies are clear.
“(Usually) you won’t get many chances to use eclipse glasses in your life. But because we get two occasions to use them within the coming weeks, it’s probably worthwhile buying a pair,” said an official at the National Astronomical Observatory of Japan.
However, experts warn the glasses must be used properly to avoid eye damage. There were 15 cases reported of eye damage from the July 2009 eclipse. In the most serious case, one person was left with a black spot in his field of vision.
It’s important, experts say, to use glasses specifically designed for eclipses, and not to rely on sunglasses or makeshift devices like black plastic bags that may result in permanent eye damage or even blindness.
Many makers and traders sell eclipse glasses, but prices range widely from a few hundred yen to about ¥2,000, although low prices don’t necessarily correlate with poor safety, said Hidehiko Agata, a manager at the National Astronomical Observatory of Japan. The most important thing is to know how to use the glasses correctly.
“Even if you have safe eclipse glasses, you could damage your eyes if you use them in the wrong way,” Agata said. “Don’t look at the sun for a long time. Keep using eclipse glasses even if your eyes get used to the sun or even when the sun is behind a cloud.”
In Tokyo on May 21, the eclipse will start at 6:19 a.m. and become an annular eclipse at 7:32 a.m. The annular eclipse will reach its peak at 7:34:30, with 97 percent of the sun hidden, and end at 7:37 a.m., with the moon moving fully out of the way by 9:02 a.m. Cities in western Japan will see the eclipse a few minutes earlier than Tokyo does.
The next annular eclipse in Japan will be viewable from Hokkaido in 2030. Tokyo won’t see another for a few hundred years, according to the observatory.
On June 6, Tokyoites will be able to see Venus blot a spot on the sun for a few hours, starting at the upper left edge, at 7:11 a.m. It will reach the upper right edge at 1:47 p.m.
Venus will appear to be one-nine-hundredth the size of the sun.
Agata said even viewers using eclipse glasses properly should take a break every two or three minutes.
Also, if the glasses are about the same size as a regular pair of specs, they may not block sunlight from the side, and thus using them even for as little as two minutes can potentially be dangerous, he added.
Since Japan has no safety standard for the glasses, companies do not need certification to produce and sell them. Agata said he could not find any eclipse glasses sold at stores that are too dangerous to use, although he added that he is not sure he saw all of the various models available.
“As far as I checked, eclipse glasses that are labeled as eclipse glasses have no problems. They all block infrared light, and you will know if they do not block visible light because it’s too shiny. If it’s too shiny, don’t use them,” Agata said.
Eclipse glasses made of film or vinyl chloride tend to be cheap. For example, Tokyo-based Hoshi no Techo K.K. sells them for ¥300 to ¥500. Those made of resin tend to be more expensive. Vixen Co. sells such glasses for about ¥1,500.
Hoshi no Techo sells models imported from France or made in Japan. Those from France are certified by German authorities, and the company has developed the Japanese-made glasses with the National Astronomical Observatory of Japan, Hoshi no Techo President Abe said.
Vixen makes eclipse glasses codeveloped with the International Year of Astronomy 2009 in Japan, a group of astronomers that began promoting safe ways of viewing total eclipses in 2009, Vixen sales planning manager Yasuhisa Tsuzuki said.