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Astronomy Gadgets Review

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Admittedly I’m a bit of a gadget freak. If it has sensors measuring the environment and produces some kind of output, I probably have one. Over the years I’ve found several of these gadgets to be really useful when pursuing astronomy and I thought I’d share some thoughts on these devices.

SQM (Sky Quality Monitor) from Unihedron. http://unihedron.com/projects/darksky/

I picked this up as “something to play with” at the Nebraska Start Party and it has become a “don’t leave home without it” tool. Basically it measures sky brightness. The technical end of it is that it counts the number of photons per arc second or something, but what it really translates to is a red LED numerical readout. You hold the unit in the direction you want to sense and press the red button. The sensor on the top of the unit reads the amount of light detected in a 45 degree cone. The numbers range from 0 (bright) to 23 (pitch black). After using the unit for a while you begin to associate the numbers with quality of the sky conditions. As an example an urban sky will measure around 18 or 19 or lower on the SQM. A reading over a 20 is getting into “fair” viewing conditions. A reading over 21 is getting into truly dark skies. Around a 22 is the most perfect sky you are going to get. At that point the SQM is measuring the stars and not skyglow. As a matter of fact I’ve seen the unit drop slightly as the Milky Way rose overhead.

A small numeric difference on the SQM will show a noticeable difference in the sky conditions. Many nights I’ve been out and have visually noticed the sky conditions changing, maybe a subtle improvement or deterioration, and the SQM can be used to confirm and quantify the observation. Perhaps a high haze layer has come in and muted the stars somewhat or a low fog layer is scattering more ground light. Earlier in a night I might have obtained a reading of 20.21 and now I might be getting a reading of 20.18 or so.

I’ve found the SQM to be very consistent. I usually take three samples of a given area of the sky and have found that each reading, if not exact usually varies by only a couple hundredths. The SQM is sensitive enough to “find” the best areas of the sky to view or image. Since it senses in a 45 degree cone, one area of the sky may read differently than another area. In the instructions it said you can also use a paper towel tube over the sensor to target a specific area of the sky rather than a cone but I have not tried this.

Another really handy use for the SQM is to compare dark sites. Granted if the measurements are not taken at the same time or under the same sky conditions there will be variations, but it is a way to roughly quantify one site or star party against another.

A nice touch is that the SQM also has a temperature function. If you hold the red button after the after the sky measurement is taken it will also give a temperature readout in Celsius and Fahrenheit.

These units go for about $120 dollars but from a long term standpoint the SQM is a worthwhile investment. It’s made in Canada by the way.

IR Thermometer.

These little gadgets are pretty common now and retail for about $30 dollars. They use an inferred beam to remotely sense temperature. The more expensive and professional units are “gun like” and others are about the size of a worn bar of soap. I picked up a Radio Shack version for $15 bucks at a swap meet. The previous owner had used it to locate hot spots and cold air leaks in his observatory and had no further need for it. That’s one use, but there are a couple others I’ve found helpful.

Probably the most useful is sensing the temperature of a mirror to see if it is chilled down to ambient temperature. Usually I take a reading of a surface that should reach ambient temperature quickly and then shoot the mirror. This eliminates the guesswork as to how long to run a mirror cooling fan.

If your equipment is inside your vehicle it’s also nice to be able to get a temperature reading on it to make sure it isn’t baking. Just open the window and shoot various areas of the equipment and see what the temperature actually is. No more guess work.

If you’re at a star party and have your equipment set up, it’s also a handy way to monitor what you have set up in direct sunlight. Is the scope really remaining cool under that tarp or is heat building up? Again no more guesswork.

When setting up equipment you could use it to check to see if that concrete or asphalt is still radiating heat or has cooled.

The smaller units like the one above are cheap, light and the batteries seem to last forever. It will easily fit in a lens box or travel case.

Wireless temperature and humidity station. http://www.ambientweather.com/thorscwithhy.html

I won’t spend a lot of time on these, I’m sure everyone knows what they do, but if you have an observatory, you will want to monitor the temperature and humidity inside. A regular” weather station” with all the bells and whistles are nice but they can be costly running several hundred.

A simple wireless temperature and humidity setup like this is around $30 bucks. Excessive heat and humidity kill telescope equipment. This is cheap insurance to monitor your investment if you have an observatory or equipment shed exposed to the elements.

Kestrel 4500 Portable Weather Tracker http://www.nkhome.com/ww/4500.html

These things are made by Nielsen Kellerman, There are many different models and prices, but the 4500 is their flagship model and does it all. If you do astronomy, if you fly, if you do long range ballistics, if you hike, camp, hunt, snowmobile, sail, if you do just about anything outdoors where the weather is a factor, (or if you’re just a weather freak), this is beyond a doubt one of the coolest things since puppies, (and puppies are pretty hard to beat).

Basically it has five sensors on it. Temperature, dew point, wind speed, a compass and pressure. With these it can calculate wind speed and direction, ambient temperature, dew point, wet bulb temperature, altitude, barometric pressure, density altitude, wind chill, heat index, headwind component, crosswind component and humidity.

It can store the current conditions with the touch of a button or be set up to take regular measurements with a timer. Everything that is recorded can be displayed in graph format, or with an optional interface, downloaded to a PC. It has a backlight display and runs on two AAA batteries that seem to last forever. The unit is waterproof/resistant and even has a clear plastic cover for the anemometer that rotates into place to protect it. For all the things the Kestrel does it is very small, easily fits in one hand and is about the size of a small TV remote.

From an astronomy standpoint, being able to tell the dew point and temperature at your exact location is hugely helpful. Since you have an instant reading (and graphing capability) of the temperature and dew point, you have some indication whether the night is going to be wet or dry. As the temperature and dew point come together, you’ll know when it’s time to turn on the dew heaters rather than running them needlessly and killing your batteries before you have to.

The other features are also very useful, especially if you are at some remote dark site where accurate and up to the minute weather information is difficult to obtain. Tracking the barometric pressure is always important to weather forecasting. Knowing the wind direction and strength in advance helps you to plan which section of the sky to view or where to set up your equipment. The heat index or wind chill measurements will help you determine how miserable you going to be in temperature extremes.

The downside on the unit is the price, clocking in nearly $290 bucks. Ouch. NK does make less expensive units but the main feature of this one is the humidity sensor and ability to know the dew point. The unit is well made and the menu system very intuitive. The only weak point is the battery door which seems very flimsy and possibly easy to break. The company even makes a weather vane so you can stick the unit on a tripod to record data.

In short, the unit is pretty expensive but becomes easier to justify if you do other outdoor activities like fly, shoot or sail. The Kestrel 4500 also comes in a special “night vision” version which has a dimmer red backlight as opposed to the standard greenish backlight for $10 bucks more. I did not get that version but have not found the green “regular” backlight to be a problem.

Portable Lightning Detectors

There are basically three separate units available on the market. At different times I have had all three. These are:

Strike Alert http://www.strikealert.com/

Skyscan http://www.skyscanusa.com/products/

ThunderBolt http://www.spectrumthunderbolt.com/

A lightning detector does just that. It has circuitry that detects the electromagnetic discharge from a lightning bolt and estimates the range and displays it. None of the units are infallible and all of them won’t work in a vehicle or around TVs, refrigerators etc but they will work indoors or out. They generally need to be about 5 or 10 feet from an electronic source or engine. All the units have some kind of an audible warning beep when strikes are detected or a range limit has been crossed, (and the tones can be silenced as well). All units are primarily battery operated but the Skyscan and ThunderBolt also have AC or DC adapters available as well. To work properly all three units have to be oriented in some way, usually vertically or in some cases, horizontally. They really can’t be hand held in any orientation and work properly. This causes more of a problem with some units than you would expect.

From an astronomy standpoint, let’s hypothesize how one of these can be useful. You’re at a dark site or star party with limited access to radar or immediately local weather. Thunderstorms may form and there are heavy cumulus buildups and a lot of convective activity all around. You hear thunder. At that point the storm is probably within 5 miles and if it is moving toward you, you have about 10 minutes to get your gear safely stored or seek shelter. With a lightning detector you’ll normally have about an 30 minutes to an hour’s notice to prepare.

If you are on the water in a boat, (especially a sailboat with a big aluminum mast), it is really handy to have that hour’s warning of approaching lightning. The units are not infallible though, the units can only sense current lightning. The detector can give no warning time if a cumulus cloud happens to turn into a thunderstorm right above you. It’s rare but it can happen. Usually though, storms are associated with an approaching cold front or unstable air masses and storms will be forming or moving into the area so you do get the warning ahead of time.

While at home I’ve watched radar as a squall line comes in and watched the detection units to see how accurate they are. I believe they work on the principle of the signal strength of an “average” lightning strike. In other words if there is a nearby weak strike it will read as further away, where a more distant strong strike will read closer than it really is. Generally though, the ranges indicated appear to be fairly accurate for all units. Most units appear to detect cloud to ground lightning but detecting cloud to cloud is hit or miss. In the case of the ThunderBolt, its programming is designed to ignore cloud to cloud lightning. When comparing the units I may see a visible flash and one unit will catch the flash, but not the other. Generally though all three units will detect strikes fairly consistently and give you the needed 30 minutes to a hour to get your gear packed up or secured.


This was my first portable detector and from my experience the best of the three. The four ovals on the face are red LEDs that indicate the range of strikes detected. The first oval is 20-40 miles, then 8-20, 3-8 and finally 3-0. There is also a “Severe Thunderstorm” light but in 10 years I never saw it come on. This unit is basically square and about the size of a thin brick (but very light). It can stand upright and has a belt clip. The unit is bulky to carry on the belt clip and it makes it difficult to see the red LEDs. If you are in one place like your observing site, tent or camper the unit can be placed on a table and read from just about anywhere in the area. The LEDs on the front are are easily visible. Even in the dark, when a strike is detected, the LEDs are spaced out enough that you have a pretty good idea which “range light” is illuminating.

It is powered by two 9 volt batteries which give about 50 hours of service. The manufacturer specifies the maximum range to be 40 miles which seems pretty accurate. The unit sells for about $180 dollars. The unit is well built and doesn’t have much in the way of design flaws. It stands up but also “leans back” to some extent so it has a tendency to fall over if bumped. It is bulky to carry but it’s the best unit if you are staying in one place. There is a tone on/off button and a “battery saver” feature. An AC or DC adapter is also available as well as a wall plate to hang it. Just make sure it is not near (within about 10 feet) any electrical currents or devices.

Strike Alert

The strike alert is about the size of a pager and designed to clip onto a belt. The range and power LEDs are on top and the only button is the power button. The ranges on this unit are a little different, 20-40 miles, 12-24 miles, 6-12 miles and within 6 miles. If you hold the power button it will also indicate whether it thinks the storms are coming, going or stalled. This unit is powered by one or two AAA batteries. The battery life seems to only be about 15 to 20 hours before a change is necessary.

I picked one of these up as a more portable addition to the Skyscan. It is highly portable and I usually keep it clipped to the sun visor on my truck or the top box on my motorcycle. It will not work accurately if the vehicle is running, but handy to have once you get someplace. It is the cheapest of the three units and appears to be slightly less sensitive than the Skyscan but will still give adequate warning time of approaching trouble.

This unit is very nice if you are “on the go”, hiking, jogging etc. If you are in one place or not standing, it gets a little difficult to use. The unit needs to be oriented vertically, (so if you’re sitting or laying down, you have to take the unit off and stand it up on a flat surface). Since the LEDs are on the top (as opposed to the side like the Skyscan), with the unit standing up, you have to be looking down from above to read the LEDs. The unit is small so the LEDs are spaced close together and it is difficult to tell one range LED from the one next to it unless you are real close. The range LEDs are color coded, yellow and red, but it is still difficult to tell which red or yellow is lighting up especially in a dark environment.

If you want compactness or a detector for when you’re on the move, the Strike Alert is the way to go. The week point of the unit is the on/off button. Mine is kind of flaky and in other product reviews I’ve noticed other comments. It appears the button contacts tend to wear and you have to push the button with a deathgrip sometimes in order to turn the unit off or on. The real pro side of the unit is the cost. It does a fairly effective job for around $70 dollars.


After about 10 years my Skyscan died and I bought the ThunderBolt as a replacement. After reading the product promos I thought it was newer technology and had more capability to warrant the +$300 plus price tag. I have been sadly disappointed by this unit. The problems are not so much with the functionality of the unit but the actual design. Its size, weird shape and recessed LCD make the unit a royal pain to use. With the other two units, just a glance at a range LED is all that is needed to see where the nearest strike is. With this unit you have to wait for it to scroll though several useless messages like “Warning!!!! Strikes Detected!!!” before you get to the range information. It gives storm arrival time and time to clear information in 15 minute increments that are too broad to really be useful. The unit does have an LED on top that is green and turns red when strikes are detected. The LED is bright enough to be intrusive at night and because of its weird shape, looks like a Battlestar Galactica Cylon.

The LCD is recessed so it makes it difficult to read the top line without looking straight at the unit. On my version the LCD is not backlit which means a flashlight would have to be used to read it in the dark. The vendor has since come out with a newer version with a backlight. The size and shape of the thing make it impossible to fit in a pocket and without a belt clip makes it necessary to carry. It does come with a large, bulky blow molded plastic case which takes up even more room. The case only fits the unit not the base, so that has to be carried separately. There is a bulky belt pouch that the vendor offers instead of a belt clip.

From a performance standpoint the unit does offer the farthest detection of lightning, out to the advertised 60 or 70 miles. When the storms get closer though it seems to consider anything within 10 miles “right on top of you”.

Because of the high price and difficult functionality I would not purchase this unit again. As a matter of fact I am going to be replacing it with another Skyscan because it is so annoying to use.

So in general, from a gadget perspective, these are some of the tools I’ve tried or have found useful for astronomy. I hope it gives you some ideas that may be useful to you.

Clear skies.


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