New Moon Saturday

A line of big telescopes greeted the crowd. Mike had his 20″, Cliff his 24″, my 18″ Deep Violet, later in the evening Olivier set up his 18″ Priscilla. All of this large glass was open to the public, we each had long line of folks waiting a turn at the eyepiece. It was a huge Saturday night crowd, several hundred people awaited darkness. Yes, I had made the decision to observe from the VIS, knowing that there would be a crowd, but wow!

Observing at the VIS
A line of big ‘scopes to greet a huge Saturday crowd at the MKVIS
Lots of folks wondered why there were so many telescopes. Over and over we explained that they were lucky, having chosen the right night to visit the mountain. A Saturday night close to the new moon, with local amateurs bringing their own telescopes to share.

Showpiece objects, the Andromeda Galaxy, The Pleiades and Jupiter were available for viewing. I was stuck on the Orion Nebula all evening long. I changed targets once, to meet a chorus of request to move back to the nebula. I have to admit it was a pretty view, even to me, who has seen this sight more times than I remember. I put the 35mm eyepiece in place, creating a bright low power view that had visitors waiting through line a few times for second and third looks.

In addition to the big dobs there were quite a few smaller ‘scopes present. Maureen had her C-11 setup, Larry brought his nice Stellarvue 102mm refractor, Mike had an 8″ SCT beside his 20″ for use by a friend. Dan didn’t bring a ‘scope, but he did bring pizza! We met Woody, an Alaskan Airlines pilot flying the Anchorage to Kona run. Out of a couple carry-on sized bags he produced more telescope than we would have thought fit in airline luggage…. A neat collapsible pier arrangement with an alt-az mount and a very nice WO 110mm APO.

Continue reading “New Moon Saturday”

Halloween Sidewalk Astronomy

For many years it has been my tradition to setup a telescope on Halloween. A tradition I have inherited from other amateur astronomers, a tradition I intend to continue.

Princess at the Telescope
A Halloween princess looking through the telescope while we were set up at the King’s Shops
Unfortunately there are few trick-or-treaters in my own neighborhood. We are somewhat at the end of the street and at the top of the hill.

Looking for an alternative to setting up in the driveway, as I have in the past, I instead arranged to setup at the King’s Shops in the resort at the bottom of the hill. The shops make an evening of it, with various entertainment and activities arranged for children and adults. Contacting the Kings Shops management I was able to arrange permission to set up a few telescopes for the evening.

Cliff and Maureen volunteered to join me, bringing more gear. We had a few other club folks drop by. Also helping out were Dean and Melinda Ketelsen, fellow Tucsonans who share the Halloween telescope tradition and happen to be visiting for the week.

Unfortunately clouds hampered us in the early evening. As usual these cleared as the night progressed so that by 8:30pm we had a mostly clear sky. Moonrise provided a beautiful view, followed by Jupiter. There was a steady flow of folks checking out the telescopes. Princesses, Batman, ninjas and more had views of Alberio, Andromeda and other celestial objects. A fun evening for everyone, mixing in just a bit of science education, just what sidewalk astronomy is all about.

Enjoying the Moonlight

Deb and I did a volunteer evening at the VIS last night. A great night with a great crowd, the sort of evening that defines the reason we continue to volunteer at the Mauna Kea VIS. Lots of great questions, great conversations and a little learning about the sky and Mauna Kea. As the southern cross hung above the slopes of Mauna Loa my green laser was busy pointing out constellations and bright stars.

The only real problem with the evening was the nearly full Moon hanging in the sky. The bright moonlight drowning out many of the deep sky objects we would normally view. Even bright objects like M13 were merely dim smudged in the eyepiece in place of the beautiful sights they offer under darker skies. With these conditions much of the telescope viewing was concentrated on the Moon and a beautiful planet Saturn.

One activity that is always a hit with a bright Moon partly makes up for the loss of dark sky viewing. I hold and quick course in introductory lunar photography using the afocal method. Show a few people how to take lunar photos and there is soon a line of people waiting at the refractor for their turn to try a few frames. A few hints and people are quickly taking great lunar shots, a photo and a memory to take home from the mountain.

The evening sped by quickly, spent in conversation with guests from the islands and from across the US. People ask about the sky as seen from different latitudes and locations. A few visitors from other countries add their perspective. It is often interesting to hear about other names for constellations or to learn bits of folklore from many other cultures.

So often the crowd disappears an hour after dark, driven off by the cold and wind. This night many didn’t go until it was time to shut down the telescopes. I guess they were not ready to end an enjoyable evening under moonlight.

The Moon one day short of full, afocal photograph taken with a 102mm refractor, 32mm eyepiece and a Canon G9 camera.

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]