Green laser pointers are a helpful astronomy tool for pointing out objects and constellations in the night sky to others. You can use them to help other astronomers who are new to the hobby find objects in the sky or at an astronomy outreach event to educate the public. Whipping out a laser is a lot quicker and easier than attempting to show a group something on a screen, and it has the added benefit of being able to point at the actual night sky with minimal effects on anyone’s dark adaptation.
Green light is the most obvious color to the dark-adapted eye and thus requires the least brightness to be seen. This has benefits for safety, power consumption, and preserving astronomers’ dark adaptation when using one. Don’t buy any laser that isn’t green for astronomical purposes (except a laser collimator, which is usually red).
Safety Comes First
Green laser pointers can be a useful tool for astronomy, but it is important to use them safely and legally.
Due to the lack of regulation from online sellers, green laser pointers rarely fall exactly within their advertised power range. Underpowered lasers are, of course, too dim to be useful. Good green lasers for astronomy are supposed to be around 5 milliwatts. This is the upper limit of laser safety/wattage class 3A, which is “safe” in that it cannot burn things but is still a risk to eyesight.
Class 3A lasers are legal in most countries, with some exceptions; for instance, Australia does not allow anything above Class 2, but plenty of sellers lie about wattage and sell Class 3A and 3B lasers anyway. If you buy a laser that you know is more powerful than the legal limit where you live, you are committing a crime (and if it’s above class 3A, you’re also needlessly taking a risk). Most countries limit lasers to class 3A or weaker.
Unfortunately, many of the most overpowered green lasers sold online are actually between 10 and 50 milliwatts, belonging to laser safety class 3B, even if they are advertised as being only 5 milliwatts. These are bright enough that just the “dot” from the laser pointed at a wall is bright enough to irritate or even damage your eyes, though they’re still safe, if perhaps a little bit too bright, for astronomy.
Considering that even the weakest laser pointer still has the power to cause eye damage if handled incorrectly, you should always practice precautions as if you were holding a laser powerful enough to burn things. Most people do not do so, causing needless harm because they cannot be bothered to treat these tools with respect.
Never point a laser beam at anyone’s eyes, as the beam can cause serious eye damage. If you’re using your laser at a stargazing event where other telescopes are present, avoid aiming the laser in the direction that other telescopes might be pointed. Your laser could be picked up by someone else’s instrument and ruin a photographic exposure, damage a night vision device, hurt someone’s eyes, and is generally just a nuisance. Avoid shining the laser beam at aircraft, as it can cause distractions or even harm to the pilots. It can also get you put in prison or heavily fined very quickly, as it is a felony in many locales.
Do not aim the laser beam at reflective surfaces, as the beam can bounce back and cause eye damage. Try to avoid aiming the laser at anything other than the sky. Do not use it for any other purpose. If you are in a remote location, the dot from the laser pointed at terrestrial objects could be mistaken for a gun sight, which could have disastrous implications.
A Class 3 laser like what is used for astronomy is far too powerful to be safe for playing with pets. The people saying that they do such things in reviews are foolish and are hardly role models. You will damage your pets’ eyes as well as possibly yours or another person’s. A dull red laser is better as a pet toy and much less of a danger to anyone’s eyesight, even if handled carelessly. If you have children, keep your laser hidden and the batteries removed when not in use. Explain to them why they should not use it as a toy.
Do not use a green laser pointer as a system that is always on, like in a bracket that helps you aim a telescope. These brackets are almost always a bad idea. Just because other people do it at star parties does not mean you should emulate them. Someone could accidentally stand in the beam, or a plane could fly through it. Additionally, anyone else around you with a telescope pointed anywhere near the beam might accidentally pick up its light, which will, at a minimum, ruin their dark adaptation and may cause eye damage. As a precaution, you should also avoid staring at the beam without looking away for long periods of time.
Users who don’t know how to use lasers safely are not only dangerous, but they are also making it harder for people in some countries to buy astronomical green lasers at all. Using your laser responsibly and teaching others to do so ensures that you can enjoy it safely and that these tools can continue to be used by responsible hobbyists.
TL;DR: If you only point the laser at the sky, don’t keep it on for extended periods, and make sure that no optical instruments are pointed at it, you are safe. Pointing the laser at anything other than the night sky is where things tend to go wrong. It is not a toy; don’t treat it as one.
Features to Look For
In a perfect world, we would recommend that you find a green laser pointer with a power output of right around 5 mW, both for legal and safety reasons. However, as mentioned previously, wattage ratings provided by manufacturers and sellers are pretty much just made-up numbers; plenty of “5 mW” lasers are actually 2 mW or 50 mW instead. It is unlikely that you are actually going to buy anything above 50 mW, though, so you should be fine. Just be sure to take the proper safety precautions with any laser, and if it seems too bright or too dim, return it immediately. Don’t buy from somewhere you can’t return the laser if it is not as advertised or has problems. If you can somehow find a laser that is proven to be exactly 5 mW, that would be ideal.
While you might have been spooked by that last paragraph, the good news is that the market for green lasers is somewhat self-correcting, and the majority of units sold are exactly 4-5 mW and made in the same factories. You are unlikely to accidentally buy a class 3B laser, though the possibility exists.
When it comes to trying to find a laser that is sufficiently bright for astronomy and not a dull cat toy, the important factor is to look for a laser that is big and hefty enough that it is plausible that it produces a bright beam. This sounds terribly simple, but it is, unfortunately, the best advice we can give. Small, pen-sized green lasers powered by AA or AAA batteries are often finicky to keep powered on or simply too dim.
Most of the green lasers sold today on sites like Amazon and AliExpress use rechargeable lithium-ion 18650 batteries; if possible, the USB-charged units are preferable to a laser that requires removing the battery and putting it in a dedicated 18650 battery charger. This is mainly because you will probably end up misplacing the charger, and a new one can cost as much as the laser and charger package itself did.
Do not buy a green laser with any of the silly “starlight modes” and other lens effect features; these are useless for astronomy, unsafe, and entice people to use them as toys, which is an accident waiting to happen. You can usually remove these lenses, but it might also result in the accidental removal of an infrared-blocking filter in the laser, which will make using it unsafe; your eyesight or someone else’s is not worth the risk. Just get one without the lens effects.
While the safety key featured in some green lasers looks like a nice added layer of security, most of these keys are plastic, and you could easily accidentally break one and have the laser become inoperable. In any case, the laser should never leave your hands to begin with.
Many of the green lasers on the market today are exactly the same across hundreds of brands and stores. A good green laser can be found for less than $20 USD. If you are paying more than around $25, you are being ripped off. They are sold in bulk to retailers for less than $5 per unit. Many astronomy vendors and brands are charging $30 or even $70 for lasers that are identical to the units sold on Amazon. We do not usually recommend buying telescopes from Amazon or other mass-market retailers if you can purchase them from an astronomy store instead, but in the case of lasers, you are not buying a terribly specialty or complex product, and the astronomy vendors are making a killing by repackaging these generic devices.
Here are three stargazing laser pointers that fits all our criteria: