Some
Pointers on the Use of Laser Pointers
By
Richard Tresch Fienberg
SkyandTelescope.com
This
is a typical amateur-astronomer's green laser pointer, shown with a simulated
beam. The 5-milliwatt laser is powered by two AAA batteries and emits an intense,
narrow beam of light at a wavelength of 532 nanometers. At night the beam is visible
for hundreds or even thousands of meters, depending on sky conditions. Devices
like this can be purchased for less than $100 from many sources.
Sky
& Telescope photo by Craig Michael Utter.
A
recent addition to the backyard astronomer's toolkit has been flagged as a potential
weapon in the terrorist's arsenal. The humble laser pointer, used by thousands
of skygazers to show beginners the way to stars and constellations, is coming
under fire from US federal and state authorities following several recent incidents
in which laser beams have "painted" aircraft in flight. In the most notorious
case, on January 4, 2005, a New Jersey man was arrested after allegedly shining
a laser at a small passenger jet on approach to a nearby airport. The suspect
claims he had been showing his daughter around the night sky, using his laser
pointer to direct her gaze at particular stars and planets. Now he faces a possible
jail term and six-figure fine. The incident sparked a media frenzy, with many
articles appearing alongside other news from the War on Terror.
Depending
which newspapers you read or which television stations you watch, you may hear
that handheld laser pointers — commonly available for less than $100 from a host
of retailers and online dealers — are either perfectly harmless or capable of
bringing down a jumbo jet. Naturally, the truth lies somewhere in between. Used
properly, laser pointers are quite safe. But used improperly or maliciously, they
can be dangerous indeed.
Here
is some basic information about the laser pointers typically used by amateur astronomers,
along with some tips on using them safely.
Laser-Pointer
Basics
The
pointers favored by stargazers use a neodymium diode laser and emit a green beam
at a wavelength of 532 nanometers. At a given power setting, such lasers appear
much brighter than the older helium-neon lasers, which produce a red beam at wavelengths
longer than 630 nm. The reason is simple: the human eye is much more sensitive
to green light than red light.
Except
on nights of exceptional clarity and near-zero humidity, if you shine a green
laser pointer into the sky, you can follow the beam hundreds of meters up. To
you and anyone standing around you, it looks like the beam ends at whatever star
or planet you're aiming at. This makes it really easy to show someone a particular
celestial object. Just point the laser at it and say, "Look there!"
Most
laser pointers shine only as long as you hold down a button. But some models have
a "constant-on" setting. These are becoming popular as pointing aids for telescopes.
Once the laser is mounted and coaligned with the scope, you just move the scope
around till it's pointing at your target star, and when you look in the eyepiece,
there it is!
The
green laser pointers in common use among astronomers and the general public have
a power output of 5 milliwatts. Compared with incandescent light bulbs, which
draw tens to hundreds of watts (not milliwatts), this sounds like very little.
But laser light is highly concentrated into a very narrow beam. Moreover, this
beam is highly collimated, meaning it diverges (spreads out) very slowly. Laser
pointers typically emit a beam about a millimeter in diameter. Even as far as
a kilometer away, the beam is no more than a meter across.
According
to engineer Samuel M. Goldwasser, who maintains an extensive Web site about lasers
called Sam's Laser FAQ, if you were to look directly into a laser-pointer beam
from a mile away, it would appear as bright as a 100-watt bulb seen at a distance
of less than 100 feet. Most people would find such a bright light very uncomfortable
and would instinctively blink and/or turn away.
Lasers
used in industrial applications and outdoor light shows are vastly more powerful
than personal handheld units. There is no question that such lasers can be harmful
to pilots, so their use is regulated, and airline pilots are trained to avoid
them. The problem with personal laser pointers is that there are millions of them
in consumers' hands, and there is no way to guarantee their safe use. In many
states, it is already a misdemeanor to shine a laser pointer at a person or vehicle.
Now that these devices are being talked about in the context of airplanes and
terrorists, there's a very real chance that they will be outlawed. Indeed, 5 mW
green lasers are already banned in the United Kingdom.
Safety
First
Direct
viewing of a laser-pointer beam, even briefly and at a distance of a kilometer
or two, has the potential to cause temporary flashblindness — the same effect
you get right after a flash photo is taken — or afterimages. These effects last
anywhere from seconds to minutes. Glare, which is a reduction or loss of central
vision, lasts only as long as exposure to the beam. All these effects could be
disastrous if they struck a person operating machinery, driving a car or truck,
or flying a plane. Fortunately, there have been no reports of laser-related accidents
of this type so far.
To
help keep it that way, we offer the following safety tips for amateur astronomers
and anyone else using a laser pointer. These are based on suggestions from the
Laser Institute of America:
Laser-Pointer
Safety Tips- Laser
pointers are designed to illuminate inanimate objects. Never shine a laser pointer
toward any person, aircraft, or other vehicle.
- Never
look directly into the beam of a laser pointer of any type.
- Do
not allow children to use a pointer unsupervised. Laser pointers are not toys.
- If
your telescope is equipped with a laser pointer that has a "constant-on" setting,
do not leave the instrument unattended with the laser switched on.
- Do
not aim a laser pointer toward mirrors or other shiny surfaces. The reflected
beam may inadvertently strike someone in the eye.
- Do
not aim a laser pointer skyward if you hear or see an aircraft of any kind flying
overhead.
- Be aware of
irresponsible uses of pointers so that the psychological effect will be minimized
if you happen to be illuminated by one.
- Do
not purchase a laser pointer if it does not have a "caution" or "danger" sticker
on it identifying its class. Report suspicious devices to the authorities.
|
"Green
laser pointers are the best way we have found to point out objects in the night
sky to the public," says Monty Robson, a commercial airline pilot and avid amateur
astronomer. He regularly conducts observing sessions for high-school students
and their families at the John J. McCarthy Observatory in Connecticut. "I would
be very disappointed," Robson adds, "if these useful educational tools became
restricted by law." Amateur astronomers can help minimize the risk of such an
outcome by using common sense, following the safe practices outlined above, and
educating others about the safe use of laser pointers.
Rick
Fienberg is editor in chief of Sky & Telescope. He enjoys using a laser pointer
to introduce the constellations to friends and relatives who visit his dark-sky
observatory in New Hampshire.
