Safe Solar Viewing

You have heard it before, but it really is true! Looking at the Sun for longer than a few brief moments with an unprotected eye can lead to permanent damage. Looking at the Sun with any sort of optical deceive that has not been properly filtered can lead to instantaneous eye damage.

Sunspot AR2192
The complex sunspot AR2192 visible on 24 October, 2014

Discussed below are the only safe methods I am aware of to view the Sun. There are some dodgy methods out there. Take chance with your irreplaceable eyesight? I think not. Be careful and do it right if you want a look.

For the unaided eye there are a couple options to view the Sun safely…

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Guardrails on Mauna Kea

Guardrails? What is the problem? It is only a few hundred feet to the switchback below. As if taking all of the fun out of Saddle Road is not enough.

Mauna Kea Guardrails
New guardrails added to the summit road on Mauna Kea
I suppose the addition is not such a bad idea, the road is a little safer.

Mauna Kea Support Services is overseeing the addition of guardrails on quite a few of the more dangerous places on the summit road. This includes the lower side of each of the hairpin turns for the switchbacks. Notable curves are getting the same treatment.

The new rail locations include the spot where a red jeep went off the road a few years ago, killing the driver and a passenger.

MKSS had made a number of safety improvements to the mountain facilities over the last few months, part of a concerted effort. New speed bumps at the visitor center, guardrails, and plans for new signage along the road.

Visitor and observatory traffic on the mountain is increasing, so is the attention from state officials. With the new comprehensive management plan in place, and groundbreaking for TMT not far off, now is a good time for it.

Getting to the Lava

Note: This post has been revised based on current conditions and access. You can see the revised post here.

Getting close to flowing lava is a great experience, but one that is fraught with risks. Sometimes the lava is relatively easy to access, near a road or developed trail. Most of the time it takes a serious hike across the old flows to get near, an arduous trip with no trail or map to guide you.

Kupapa'u Lava
An active pāhoehoe breakout at Kupapa’u

My most recent hike was my fifth trip out to the flowing lava, requiring my longest hike over the flows to date at just under three miles each way. OK, maybe I am not yet a veteran, but these trips have taught me a lesson or two. Going onto the lava is an inherently risky proposition and one must accept that risk. With a little knowledge and preparation the risks can be mitigated. Besides, the reward is spectacular!

You can take my word for it, or perhaps read the same information from someone who has been out far more than I. We will all tell much the same story.

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Trek to the Lava

The lava has been entering the sea for over a month now. I have wanted to hike out, but life and other commitments have consistently intervened. With off-island guests, I made the offer to lead a hike out to the flowing lava. My sister-in-law Darcy was the only one that took me up on the offer, the prospect of a 2am wake-up and a two hour trek across rough ground too much for some. We left the others in bed.

Kupapa'u Lava
A active pāhoehoe breakout at Kupapa’u
This is the same plan I have used before, a two hour run across the island to Kalapana gets us to the edge of the flow field about 4am. This leaves another two hours to hike to the lava flows. We would need the time! It would take all of that two hours to make just 2.7miles. Two hours over the rough ground of older lava flows, avoiding pits, loose plates, large cracks and small hummocks that rose 10-20feet overhead. This was in pitch black conditions with no moonlight to help. It was alternating bright stars and clouds overhead, two brief showers left us dampened but comfortable in the warm tropical dawn.

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Visiting the Summit of Mauna Kea

Visiting the summit of Mauna Kea is high on many visitor’s to-do list when coming to the island. The summit region is spectacularly beautiful, even after six years of visiting several times a week I still find it so. My habit is to drive, or to ride shotgun in order to enjoy the view. I keep a camera at hand, ready for the inevitable situations where beautiful is transformed to spectacular with a well placed cloud or shaft of sunlight.

Summit Visitors await Sunset
The usual crowd of summit visitors await sunset along the ridge between the Gemini and CFHT telescopes
Any visit to the summit starts by stopping in at the Mauna Kea Visitor Information Center. Located at 9,200ft the center is found at the end of the paved road. The folks here are responsible for providing visitor information and helping you out if you get into trouble, a service provided by the observatories through Mauna Kea Support Services. This includes the Mauna Kea Rangers who patrol the mountain, providing information, advice and assistance to visitors. Also found at “The VIS” are bathrooms, a gift shop, and the evening star gazing program.
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Safe Transit Viewing

You have heard it before, but it really is true! Looking at the Sun for longer than a few brief moments with an unprotected eye can lead to permanent damage. Looking at the Sun with any sort of optical deceive that has not been properly filtered can lead to instantaneous eye damage.

Discussed below are the only safe methods I am aware of to view the Sun. There are some dodgy methods out there. Take chance with your irreplaceable eyesight? I think not. Be careful and do it right if you want a look.

For the unaided eye there are a couple options to view the Sun safely…

  • Solar Viewing Glasses Proper solar viewing filters are made from a thin plastic film, usually mylar, coated with metal to properly filter the Sun’s light for viewing with the unaided eye. These are widely available and quite cheap. Local astronomy organizations have been giving them away in preparation for the transit. Do not attempt to use these viewers in conjunction with binoculars or small telescopes, they do not provide sufficient filtering for optics!

  • Welding Glass Filters used for viewing welding offer much the same protection as solar filters. A shade 13 or darker welding filter can provide good protection for the unaided eye. Again, do not use a welding filter with any sort of optical device such as binoculars, they are not designed for such use and may not block enough light.

A much better view of the event can be seen if modest magnification is used. Do keep in mind that any soft of binoculars or telescope also concentrates much more light that the eye alone. Remember those childhood “experiments” involving a magnifying glass and ants? The best options here are the use of solar filters designed to be used on a telescope, or indirect means such as image projection.

Solar Filter
A solar filter mounted on a refracting telescope

  • Solar Filters for Telescopes Filters specifically designed for telescopes consist of either a plastic film, or a sheet of glass, coated with a thin layer of metal to block the Sun’s light. These filters pass about 1/1000 of one percent of the light. More importantly, they block the harmful infrared and ultraviolet light that could so easily cause damage. The filters can be purchased in many sizes as appropriate for various models of telescopes, costing between one hundred and several hundred dollars.

  • Image Projection One of the simplest methods of displaying a solar image is projection. A white screen placed a foot or two behind a telescope will produce a very nice image of the Sun that can be safely viewed by a number of people simultaneously.

    Keep in mind that the beam of light out of the eyepiece is quite intense, potentially hot enough to burn a careless finger placed near the exit from the telescope.

    The method works best with small optical systems, binoculars or the smallest of telescopes. You do not need big optics to project a very nice solar image.

    You do not have any optics? Use the simplest optical arrangement of all, the pinhole camera!

If you do not have a safe means of viewing the transit and do want a look, you can go to one of the many public events being organized. Here on the Big Island there are quite a few options, one should be close to you.

Transponder Based Aircraft Detection

When you shine a powerful laser into the sky, someone is likely to notice.

That someone is likely to be the Federal Aviation Administration, who, for some reason, seem to be concerned about the possibility of our illuminating a passenger airliner with an AO laser.

Both Keck lasers in operation
Both the Keck 1 and Keck 2 lasers in operation under a nearly full Moon
We currently use laser spotters to insure this does not happen. Yes, some poor soul must sit outside all night long and watch the skies for aircraft near the beams. When the weather is nice this is not a problem. It is seldom that nice, a bitterly cold wind is the usual condition. I have done this duty, for about an hour, and really do not need to do it again. After a night in the cold, is a person really an alert observer? An automated system that removes the human element from the equation is really a better solution.

Enter TBAD, the Transponder Based Aircraft Detector. All commercial and most civil aircraft carry a 1090MHz ADS-B transponder that identifies the aircraft and provides basic data. The transponder is part of an aircraft tracking system now used by air traffic control centers around the world to supplement, or in some cases replace, radar systems. An idea… Create a directional antenna that can determine if a 1090MHz transmitter is in the beam of the antenna and mount that antenna to the telescope. With such a system we can detect an aircraft approaching our beam and shutter the laser. The idea was conceived by Tom Murphy and Bill Coles at the University of California San Diego. Thus TBAD can alternately mean Tom and Bill’s Aircraft Detector.

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Lasers and Aircraft

Those of us who use green lasers for astronomy outreach are always worried about law enforcement cracking down on these devices. As the lasers get cheaper and more available they inevitably get into the hands of those who do not use them responsibly. Worse, the lasers are easily available at power levels that are truly dangerous.

Laser and Stars
Deb pointing out the star βPhoenicis to VIS volunteer Joe McDonough
The problem has continued to escalate, each year there are more reported incidents of aircraft being illuminated by the laser of some idiot (yes, the correct term) who thinks it might be cool to tempt fate and the law. In 2010 there were 2836 incidents reported to the FAA, up from only a few hundred a few years before. With this sort of trend it seems inevitable there will be some sort of official reaction.

Illuminating an aircraft with a laser can be prosecuted under federal law. Not because there is any specific statute addressing lasers, but as it is deemed “Interference with a Crewmember” using an interpretation of a pre-existing 1961 federal law, specifically 14 CFR 91.11.

The FAA has put together a new webpage on lasers and aircraft safety. The page organizes and links some informative resources. This includes a couple reports on the possible effects of laser illumination on aircraft crew, as well as the legal and regulatory recommendations of the FAA. I urge anyone who uses these devices to follow the link and do a little reading.

Used responsibly these lasers are extraordinarily useful in astronomy education. Nothing grabs the crowd’s attention so quickly as that brilliant green beam. Everyone can follow along without confusion as objects are pointed to across the sky. From the constellations to the Milky Way, satellites, planets and zodiacal light, on to star clusters and galaxies, everyone knows right where to look. I do prefer lasers in the 20-30mW range, bright enough to be seen by a crowd, even under moonlight. Not powerful enough to easily injure in the case of a brief exposure to the beam.

Public Astronomy Laser Power and Safety

How bright a laser beam is needed to allow good public presentations and a good astronomy education experience? In the United States legal green lasers are limited to 5 milliwatts (mW) by the Food and Drug Administration. Many of the lasers sold as 5mW are actually 3-4mW as it is necessary to stay below that limit if you wish to import the laser into the United States or to sell the laser across state lines. 5mW units are fine if you are under fully dark skies, but often you are not, there are city lights, or moonlight and the 5mW beam ceases to be usably visible. This is worse if you are working with a larger group and the distance from the presenter is larger, also making the beam less visible. In practice I have found a beam in the 20-30mW range is about ideal. These lasers are available from a number of sources for around $100. Good visibility in moonlight, good visibility in light polluted surroundings and good large group utility. But importantly, not powerful enough to be truly dangerous.

Laser and Stars
Deb pointing out the star βPhoenicis to VIS volunteer Joe McDonough
Where does the 5mW limit come from? The FDA, being a very conservative organization, set the safety threshold at 5mW based on animal and human studies and medical injury data. The 5mW limit is a national standard and applies to interstate or customs transactions, not all states have adopted it. Hawai’i does not appear to have strict laws regarding lasers, licensing or use, so my 30mW unit is legal. This contrasts with my previous home in Arizona, which is more typical of many states. The use of a class IIIb device was subject to licensing, training requirements, and yearly fees. The agency responsible being the Arizona nuclear regulatory office. Sheer bureaucratic overkill that made it practically impossible to legally use a device in the power range I needed, just a few milliwatts over the limit. I am always surprised there is no intermediate class, that a 20-30mW device is classed with devices of up to half a watt, devices that are quite dangerous.

How do I come up with the 20-30mW number as being relatively safe? Being an engineer I understand safety margins and over specification and figured there must be a compromise. The trick was to find undistorted data, without the bias of overcautious bureaucrats. The data is out there on the web, but took some digging to find, many medical journal articles are hidden behind subscription services. Fortunately there are sources like PubMed that are freely and publicly accessible. Eventually I found and read several very informative papers on lasers and eye damage, looked at pictures of laser damage on monkey retinas and looked a damage done by visible lasers in the same sort of power class as those available for public work. I was surprised by actual human damage studies, done on patients who were having eyes removed due to conditions like cancer, where the researcher could do damage without harming the patient. What I was looking for was just what level of laser radiation is dangerous in practical use.

Lasers at the VIS
Green lasers in use at the Mauna Kea VIS nightly observing with the Milky Way high overhead
The conclusion I came to was that a 20-30mW unit could cause damage, but was not excessively risky. The data in the papers showed you could generate damage to a retina with even a 5mW device given a long (60s) exposure. But there were a lot of caveats, the beam had to be well focused, the eye could not be moving and it had to be focused for a substantial length of time. In reality a number of things protect the human eye, the first is the fact that the eye is constantly moving, this spreads the power over more than one spot, not allowing cumulative damage at one site. The second is that a bright visible laser will initiate a blink reflex, keeping any exposure in the tens of milliseconds time scale. To prevent these protective effects the tests in the references were sometimes done with anesthetized subjects. At the 100mW power level damage occurred with very short exposures and was quite dramatic.

A 20-30mW laser needs to be treated with respect as injury is possible, but no more than any other dangerous tool we use every day. In practice damage with a laser at a sensible power level (20-30mW) would require prolonged exposure (>0.5sec) on a single site on the retina, requiring staring into the beam. The bright green light would elicit both a blink response and an aversion of the head and eye, particularly in a visually dark adapted environment. I would strongly discourage use of any laser 50mW or greater for public astronomy work. Some of the references showed significant damage inflicted with 50mW lasers and sub second exposures. Lasers at all power levels should be kept out of the hands of anyone too young to understand the implications of the danger posed by a laser.

Retinopathy From a Green Laser Pointer, Dennis M. Robertson, MD; Jay W. McLaren, PhD; Diva R. Salomao, MD; Thomas P. Link, CRA, Arch Ophthalmology 2005;123:629-633 [Note: direct testing of a 5mW green laser pointer on a human subject]

A comparative histopathological study of argon and krypton laser irradiations of the human retina, J Marshall and A C Bird, Br J Ophthalmology 1979 October; 63(10): 657–668

Histopathology of ruby and argon laser lesions in monkey and human retina. A comparative study, J. Marshall, A. M. Hamilton, and A. C. Bird, Br J Ophthalmol. 1975 November; 59(11): 610–630

Maculopathy From Handheld Diode Laser Pointer, Clive H. Sell; J. Shepard Bryan, Arch Ophthalmology, Nov 1999; 117: 1557 – 1558.

Assessment of Alleged Retinal Laser Injuries, Martin A. Mainster, PhD, MD; Bruce E. Stuck, MS; Jeremiah Brown, Jr, MD, MS, Arch Ophthalmol. 2004;122:1210-1217. [Note: good general discussion on the issues of laser injury and great reference list]