All I Want for Christmas is a Green Laser: How to Choose and Use One

When it comes to helping others find something in the night sky, a green laser makes it a piece of cake. Credit: Bob King
When it comes to helping others find something in the night sky, a green laser makes it a piece of cake. Credit: Bob King

Devious humans have given green lasers a bad name. Aiming a laser at an aircraft or the flight path of an aircraft is illegal according to a 2012 U.S. federal law. Jail time awaits offenders. Don’t point at a police officer either. To get a taste of the dark side of green lasers, check out these rap sheets.

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A standard 5 milliwatt (mW) laser can cause temporary flashblindness or at the very least distract a pilot up to around 11,000 feet (3,350 meters). Beyond that, it’s indistinguishable from other ground lighting. Credit: Wikipedia

But if you mind your manners, a green laser is one of the best tools available to amateur astronomers eager to share the wonders of the night sky with the public. There’s simply nothing better to point out constellations, comets, individual stars and satellites in the night sky. Amateurs love ’em! So does the public. Go to a star party and pop out the laser, and you’ll get everyone’s attention. There’s magic in being able to point out our favorite points of light with a beam of light.

Not only are lasers helpful when pointing out stars, many amateurs use them to point to and find deep sky objects with their telescopes. Credit: Bob King
Not only are lasers helpful when pointing out stars, many amateurs use them to point zero in on deep sky objects with their telescopes. Credit: Bob King

First, let’s look at laser etiquette to ensure the safety of our fellow stargazers:

* Always gather the group around you first, raise the laser above the crowd and ask everyone to look up. Then turn on the beam and aim. That way no one will accidentally face into the light. This is crucial when aiming low above the horizon, where the beam, nearly horizontal, has a better chance of striking someone in the eye. Take extra precaution to make sure the group is close. The closer the gathering, the brighter and easier the beam will be to see. Viewers too far off to one side or another will see a weaker, less intense light.

* Green lasers often use AAA batteries and draw a good amount of power especially on chilly nights. You’ll only get a few minutes of operation if you leave it out in the cold. Store your laser in an inside pocket to keep it warm until you need it. Tuck it back in between pointing sessions. Have a fresh pair of batteries around and keep those in your pocket, too!

* If you see an airplane headed in your direction, avoid using the laser light for a couple minutes just to be on the safe side.

* Never give your laser to someone in the dark to “try out.” Especially a child! They won’t be familiar with its safe use.

* Store your laser in a safe place when not in use, so kids can’t accidentally find it.

Red, green and violet lasers with a high enough output to trace a line in the night sky are all available now for reasonable prices. These three beams come from 50 mW lasers. Credit: Bob King
Red, green and violet lasers with a high enough output to trace a line in the night sky are all available these days for reasonable prices. These three beams come from 50 mW lasers. Multiple rays result from the subject not being able to hold the lasers steady during the time exposure! Credit: Bob King

The most common green laser available is rated at 5 milliwatts (mW), just adequate for night sky pointing. That said, be aware that brightness from one manufacturer to another can vary. Some 5mW pointers produce nearly as much light as a 30 mW model, practically a light saber! Others, like my first green laser, did the job on moonless nights, but proved too weak by first quarter phase. 30mW and 50mW are much better and significantly amp up the wow factor when you’re out with the crowd. They’re also much easier to see for larger groups and remain visible even in bright moonlight.

Back in olden days, 5 mW red and green lasers were as bright as they came, and the green ones were pricey. But nowadays, you can get powerful pointers in green, red, blue and violet. All will trace a visible beam across the night sky with green the brightest by far because our eyes are most sensitive to green light.

Green, violet and red lasers. Lasers emit very specific colors of light. Green appears brightest and sharpest; red and blue beams look fuzzier to our eyes. Credit: Pang Ka kit / CC BY-SA 3.
Green, violet and red lasers. Lasers emit very specific colors of light. Green appears brightest and sharpest; red and blue beams look fuzzier to our eyes. Credit: Netweb01 / CC BY-SA 3 / Wikimedia

I should add that yellow lasers have also recently become available. Like green, they’re superb for long-distance applications, but prices — oh, my — will burn a hole in your wallet. How about 300 bucks! You can get a 5 mW green laser for $5-10 that’s similarly bright. No matter what kind of laser pen you buy, they all operate on the same principle: a laser diode, related to an LED (light-emitting diode), powered by AA batteries emits a narrow, coherent beam of light when switched on.

Coherent light is light of a single wavelength where all the crests and troughs (remember, light is a wave) are in lockstep with one another. Each crest precisely overlaps the next; each trough snugly fits within the other. Regular light contains a garden salad mix of every wavelength each vibrating out of stop, to its own drummer as it were. Because laser light is coherent, it stays focused over great distances, forming a narrow beam ideal for pointing.

Lasers form visible beams because they scatter off air molecules, water vapor and dust in the air. In this photo, I spun the beam around the planet Jupiter on a humid, slightly foggy night. Credit: Bob King
Laser light literally illuminates the air and anything in it. The intense beam scatters off air molecules, water vapor and dust in the air. In this photo, I spun the beam around the planet Jupiter on a humid, slightly foggy night. Dust and water vapor illuminated by the beam creates a mesmerizing sparkle effect you have to see to believe. Credit: Bob King

Lasers are not only rated by power (milliwatts) but also the specific wavelength they emit. Green lasers beam light at 532 nanometers (nm), blue at 445 nm, violet at 405 nm, red at 650 nm and yellow at 589 nm. Green laser pointers generate their light from an infrared laser beam within the pen’s housing. Normally, any infrared light should be filtered from the final beam but in the majority of inexpensive laser pointers, it beams out right along with the green. We can’t see it, but concentrated infrared laser light poses an additional hazard when directed into the eyes.  When you hear of lasers being used to pop balloons or light a match, it’s the leaky infrared that’s doing the popping. Yet another reason to use your laser with care!

Lasers can be artistic tools, too. Every year, a friend holds a star party near a towering grain silo. Late at night, we take a break, open the camera shutter and paint the silo with laser light. In this case - a rocket. Credit: Bob King
Lasers can be artistic tools, too. Every year, a friend holds a star party near a towering grain silo. Late at night, we take a break, open the camera shutter and paint the silo with laser light. In this case — a rocket. Credit: Bob King

Lower-powered laser pointers use AAA batteries. For instance, both  my 5 mW and 55 mW green lasers use AAA batteries. Higher-powered pointers in the 5-watt range use a single #18650 (or 16340) 3.7 volt lithium ion rechargeable battery. You can either purchase these online (Orbitronics makes an excellent one for $12.99) or at your local Batteries Plus store. You’ll need a charger, too, which runs anywhere from about $8 for a single battery model to around $30 for a multiple battery version with different charging speeds. Be sure you get one with an LED light that will alert you when the batteries are done charging.

Whether sold in the U.S. or elsewhere, nearly every laser comes from China. We’ll talk about that in a minute, but if you purchase a laser that uses rechargeable batteries, beware of no-name chargers and off-brand batteries that lack safeguards. Some of these inexpensive batteries have been known to explode!

What to buy? I can’t speak to every firm that offers laser pointers, and there are many, but some of the more popular ones include:

* Wicked Lasers
*  Z-Bolt
* Optotronics
* LED Shoppe

I’ve bought from Optotronics, based in Colorado and the LED Shoppe, out of Hong Kong. I took a chance on the LED Shoppe’s lasers and have been pleasantly surprised at the low cost, free shipping and good customer service. While power ratings can vary from what the label reads, I’ve been especially pleased with both the 55 mW from Optotronics and the 5-watt (yes, FIVE WATTS) green and red pointers from the LED Shoppe. Their 50 mW green version does a great job, too. Just a disclaimer — I don’t work for and am not associated with either company.

Bottom line: If you’re looking for a effective pointer for public star parties, I recommend a 50 mW or higher green pointer. Anything in that range will provide a lovely bright beam you can use to literally dazzle your audience when sharing the beauty of the night. Before you make your decision, check your country or state’s laser use laws where for the U.S. or worldwide. If buying in the U.S., speak to the business owner if you have any questions.

Have a Merry Green, Red, Blue and Violet Christmas!

River of Fire Smoke Darkens Sun and Moon

My eyes are burning. The morning Sun, already 40° high, glares a lemony-orange. It’s meteorologically clear, but the sky looks like paste. What’s going on here?

Forest fires! Many in the Midwest, northern mountain states and Canadian provinces have been living under a dome of high altitude smoke the past few days reflected in the ruddy midday Sun and bloody midnight Moon.

On June 29, 2015 NASA’s Terra satellite captured this image of a river of smoke pouring across the Canadian provinces and central U.S. from hundreds of wildfires (seen at upper left) in western Canada. The difference in color between clouds true clouds and smoke is obvious. Credit: NASA image courtesy Jeff Schmaltz, LANCE/EOSDIS MODIS Rapid Response Team at NASA GSFC
On June 29, 2015 NASA’s Terra satellite captured this image of a river of smoke pouring across the Canadian provinces and central U.S. from hundreds of wildfires (seen at upper left) in western Canada. The difference in color between clouds true clouds and smoke is obvious. Credit: NASA image courtesy Jeff Schmaltz, LANCE/EOSDIS MODIS Rapid Response Team at NASA GSFC

Fires raging in the forests of northern Alberta and Saskatchewan have poured tremendous amounts of smoke into the atmosphere. Favorable winds have channeled the fumes into a brownish river of haze flowing south and east across Canada and into the northern third of the U.S. If an orange Sun glares overheard at midday, you’ve got smoke. Sometimes you can smell it, but often you can’t because it’s at an altitude of 1.2 – 3 miles (2-5 km).

The Moon sits at lower right with the star Vega visible at the top of the frame in this 30-second time exposure made last night (July 2) under the pall of forest fire smoke. Credit: Bob King
The Moon sits at lower right with the star Vega visible at the top of the frame in this 30-second time exposure made last night (July 2) under the pall of forest fire smoke. Credit: Bob King

But the visual effects are dramatic. Last night, the nearly full Moon looked so red and subdued, it could easily have been mistaken for a total lunar eclipse. I’ve never seen a darker, more remote-looking Moon. Yes, remote. Without its customary glare, our satellite looked shrunken as if untethered from Earth and drifting away into the deep.

And nevermind about the stars. Try as I might, I could only make out zero magnitude Vega last night. The camera and a time exposure did a little better but not much.

This image taken by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard the Terra satellite on June 30, 2015.  Residents of the states affected by the smoke will notice much more vivid sunsets during the time the smoke is in the air.  The size of the smoke particles is just right for filtering out other colors meaning that red, pink and orange colors can be seen more vividly in the sky. NASA image courtesy Jeff Schmaltz, MODIS Rapid Response Team. Caption: NASA/Goddard, Lynn Jenner
This image was taken by the Terra satellite on June 30, 2015. Residents of the states affected by the smoke will notice much more vivid sunsets during the time the smoke is in the air. The size of the smoke particles is just right for filtering out other colors meaning that red, pink and orange colors can be seen more vividly in the sky. NASA image courtesy Jeff Schmaltz, MODIS Rapid Response Team. Caption: NASA/Goddard, Lynn Jenner

These days of deep red suns in the middle of the day fiery moons at night are an occasional occurrence across Canada and the northern half of the U.S. during the summer. Our previous bout with fire haze happened in early June as a result of massive wildfires in the Northwest Territories and northern Alberta. A change in wind direction and thorough atmospheric-cleaning by thunderstorms returned our blue skies days later.

Using a prism, we can take white light and spread it apart into its component colors. Credit: NASA
Using a prism, we can take white light and spread it apart into its component colors. Credit: NASA

While the downsides of fire haze range from poor air quality to starless nights, the upside is a more colorful Sun and Moon.

Back in grade school we all learned that white light is made up of every color of the rainbow. On a sunny day, air molecules, which are exceedingly tiny, scatter away the blue light coming from the Sun and color the sky blue. Around sunset and sunrise, when the Sun’s light passes through the lowest, thickest, haziest part of the atmosphere, greens and yellows are also scattered away, leaving an orange or red Sun.

Fire smoke adds billions of smoke particles to the atmosphere which scatter away purples, blues, greens and yellows to turn an otherwise white Sun into a blood red version smack in the middle of the day.

A ring-billed gull is silhouetted against a yellow sky and orange sun early Monday afternoon. Smoke from forest fires across Canada’s Northwest Territories and northern Alberta drifted over the region and colored the the sun orange long before sunset. Credit: Bob King
A ring-billed gull is silhouetted against a yellow sky and orange Sun  in Duluth, Minn. a few weeks back during the previous series of smoky days.This photo was taken around 3 p.m. local time. Credit: Bob King

Keep an eye on the color of the blue sky and watch for red suns at midday. Forest fires are becoming more common and widespread due to climate change. If you’ve never seen this eerie phenomenon, you may soon. For more satellite images of forest fires, check out NASA’s Fires and Smoke site.

I’ve often wondered what it would look like if Earth orbited a red dwarf star instead of the Sun. These smoky days give us a taste.