All posts by AstroJim

Jim has been an astronomy and space exploration enthusiast since early grade school. As the result of a renewed interest in astronomy in 2012, he bought his first "real" telescope and mount. He has since ventured into astrophotography, and continues to acquire equipment, skills, and knowledge to improve his capabilities.

Dewy or don’t we?

I have been so drawn to this title that has been floating around in my head that I just had to start writing about it. You may find the idea of anything floating around in my head sufficiently amusing that there is no need for you to read any further.

Dew season is coming up, so we may as well get ready for it. I have done some reading on dew, but I am not yet at the expert level. My aim in writing on this topic is help me clarify my thoughts, and to help raise awareness and stimulate thought in a manner that will help astronomers meet, understand, and defeat dew.

The dew point is one of the keys to understanding dew. The atmosphere always contains moisture, sometimes more of it than others. As the temperature drops from daytime into nighttime, the atmosphere is able to hold less moisture than when it is warmer. The dew point is a function of the amount of moisture in the atmosphere, and temperature. This function yields a temperature at which the atmosphere is “forced” to begin releasing moisture as water droplets.

But this is not the final answer. Astronomers must deal with the “chilling effect” of the night sky (that we are out to observe) on their equipment. Dew does not “fall” onto the upper surfaces of our equipment, it forms there as a result of the chilling effect. Our equipment radiates heat (IR radiation) in all directions. The bottoms and sides of our equipment gets some heat back in the form of radiation from our surroundings. The clear air above us, however, does not give back nearly as much heat as our surroundings on the the ground. This causes the upper surfaces to chill faster, which in turn hastens the formation of moisture on these surfaces.

How can the weather forecast help us? I don’t know exactly, but here is a possibility. I have observed for sometime that the forecast usually predicts that during the daytime the air temperature will be well above the dew point. On most nights, and for most of the night, the temperature and dew point are about the same. Perhaps when the air temperature falls to the dew point (and probably a few degrees above that point) is when dew protection is needed. In the future, I intend to note the time in the forecast at which the air temperature drops to the dew point, and observe when dew actually starts forming. If I am in the back yard, next to my weather station (Google: Weatherunderground KMDASHTO6), it is easy to monitor conditions.

Here is another exploitable fact: both glass and painted surfaces radiate heat very well, and are both prone to collecting condensation. Using painted metal surfaces as a proxy for glass, even if we have protection in place on the glass, we can gain a sense of when and under what conditions dew forms.

A dew shield is the first line of defense against dew forming on our optics. When a telescope is not pointed straight up, dew shields give us some protection from dew. Not because they prevent the dew from falling onto the glass, but because they are a barrier between the forward facing optics and the chilling effect of the night sky above. Shields do not help much when observing near the zenith.

A slight breeze can be helpful. This is not because of a “drying” effect of the breeze, but because air that is kept slightly warmer by radiation received from our surroundings is moving over the optics. A dew shield, counterintuitively, might prevent the breeze from “warming” our optics and could actually increase the likelihood that dew will form.

The next line of defense is applied heat. It doesn’t take much heat. The optics that we are trying to protect need be only slightly warmer than the surrounding air, and not necessarily warm to the touch. Three ways to warm optics come to mind. Dew heaters, usually as strap connected to a controller that controls the amount of heat applied (and the drain on valuable and heavy battery capacity) are convenient. Probably best monitor the ambient temperature relative to the dew point and begin applying heat before the dew ever forms to avoid it all together. Otherwise one might end up waiting some period of time for optics to clear after the dew has formed. 12v hair dryer type devices are used by some astronomers, but periodic reapplication of heat is required. I have heard of astronomers using rubber bands to affix chemical hand warmers to Telrads. 

Here is an experiential data point: I turned on an Astrozap dew heater strap and controller on my 4″ refractor AFTER dew had begun to form on the objective lens at the during a photography session on October 14th. It took about 15 minutes with the power setting at full/high for the dew to clear. I turned it down to about 30% and the lens stayed clear for the remainder of the session. In the future, I plan to turn on the dew heater earlier (guided by forecast and/or actual conditions), and experiment with even lower settings. Perhaps there is some factor that I can consider that will suggest whether a lower or higher setting is appropriate.

There are many finer points to shielding and heating solutions, but I think that this a good start with regard to understanding and solving the dew problem. I think that the key to being more effective in combating dew is to be observant of forecasts, weather conditions in real time when possible vs. when dew actually forms on our equipment. Also, gaining experience with how much heat to apply (or how much of an amperage load to allow on our batteries) to keep dew from forming will be helpful as well.

© James R. Johnson, 2021.
jim@jrjohnson.net

What do I think of the OMEGON LX3 Tracker?

I received this question after posting Three Comets to Flickr, and after posting associated discussion here about the Omegon LX2. I was not aware that Omegon had released an LX3, I had to see how the two devices compared. My comparison is based upon my actual experience with the LX2, and with what I was able to glean about the LX3.

I have written about using the LX2 in two articles: Have I Ever Seen Two Comets in the Same Photo?, What Tracking was I using for Three Comets? I have also posted another image that used the LX2 in Flickr, Milky Way and Meteor with Jupiter.

The LX3 has an optical polar alignment finder where the LX2 uses a short plastic tube (more like a straw, because there are no optics). I am certain that the LX3 can be aligned more accurately, and maybe that will be more important at longer focal lengths than I have used with the LX2. I shot Three Comets at 55mm after aligning through the “straw” and the tracking looked great.

The LX3 has 60 minutes of tracking vs. 30 minutes for the LX2, which is a very nice improvement. This is important, because after the timer runs down, rewinding it moves the camera back to where the it was pointing 30 minutes ago. This means that the camera must be repointed at the star field before proceeding. Fortunately, I only wanted 30 minutes for Three Comets, because I wanted to avoid the thicker, wetter atmosphere closer to the horizon.

Improved tracking accuracy and payload capacity – I cannot speak to these. I was, however, intrigued by idea that the LX3’s clockwork ticks per minute can be measured to assess tracking accuracy at various spring tensions. Similar to the LX3, the LX2 has a spring that can be set to support heavier loads. I think that I will measure my ticks with various lenses.

That’s about it for comparison. As for Omegon LX3 being worth the extra money over the LX2. I would say that it depends. Thirty extra minutes of tracking is awefully attractive!

© 2021 Jim Johnson

What Tracking was I using for Three Comets?

Here is the extended question that I was asked shortly after posting Three Comets:

It was fun to watch you that night.  Your preparation truly paid off in a stellar way.  What tracking were you using with your Canon?  I have no experience with or software for stacking images.  On Saturday, I pushed my 14mm lens to the limit with 25 second exposures without star trailing when pointed south.  With that lens, I’m able to use a lightweight travel tripod with no tracking.  I’m considering a 70-200mm lens for my Nikon D750 for astrophotography, but I’d still like to be relatively lightweight and portable (carry on).  Suggestions?

And my answer:

Thanks, I am glad that you had fun watching me struggle and sweat with that one. 😎

Actually, I am pretty sure that I had the most fun working on this image.

My Canon was fitted with a 55mm f/1.4 lens that I had stopped down to f/2.8. It was tracking on a $160-ish mechanical wind up tracker made by Omegon. It is called an LX2 Mini Tracker. 

For anyone who already has a DSLR and a couple of lenses, this device is hard to beat for anyone wanting to get started in astrophotography without a huge up front investment. I wish that my Losmandy G-11 tracked as good as this tracker does…feel free to open the image and zoom in. There are no elongated stars in forty seven 25 second exposures. So that’s my suggestion for a tracking device. The tracker is small and lightweight, so it is perfect for travel.

I am pretty sure that I would have gotten elongated stars if not for the tracker. The tracker runs for about 30 minutes on a wind up (like winding your watch), and I got star trails in some frames after it timer ran down at the end of my run.

Stopping to reflect for a moment while writing just now, I realized a few things. This is an exception image, but it was not just me. This is a HAL image.

Acquiring the kit that I have to do this imagery, wider FoV camera lenses and the tracker, was inspired by Cheryl’s wide field imagery.

The image would not have been possible without Victor and Bob opening Carrs Mill both nights this weekend, or without my good fortune to be a member and and having access to this incredible resource.  Of course, there have been many HAL members opening the park over the years, which has given me the opportunity to learn the astronomy arts.

I have been inspired by Brad, Gene, Ken, James, Steve, John, and HAL’s many other top-notch astrophotographers. Additionally, people like Gene and James have inspired me to work carefully and take my time and read the literature on any new software that I might to use. 

Last, and certainly not least, without what you and the HAL Board (and past boards have done) does month in and month out to keep HAL vibrant and relevant, there would be no HAL to make this image possible.

I am very grateful for being a HAL member, which has having been in the right place at the right time for grabbing the torch and running with it.

© 2020 Jim Johnson

Have I ever Seen Two Comets in the same Photo?

This question came to me from a neighbor during a discussion in July 2020 about an image of Comet NEOWISE (C/2020 F3) that I had recently posted. My recollection at the time was that I had not seen such an image. A few weeks later during a Saturday morning breakfast discussion with some astronomy friends in early August, I learned that two comets would be aligned as such that they could be seen within the same camera frame, so I set about to produce an image of two comets.

The star of the two-comet scene was NEOWISE which had dominated astronomers’ attention during the entire month of July 2020. By the second week of August, however, NEOWISE had faded to magnitude 7.6. At this point it could only be seen with telescopic magnification. The other comet was PANSTARRS (C/2017 T2) at a much dimmer magnitude 10.7.

As luck would have it, as I was looking for these two objects’ placement in Stellarium, I noticed a third comet, Comet Lemmon (C/2019 U6) at magnitude 10.3. It was significantly farther from NEOWISE than was PANSTARRS, but I could still fit the trio into a single camera frame using a 55 millimeter camera lens.

Luck still staying with me, the three comets were located in a star field that included Arcturus and some other stars that would make it easier to identify the star field while I was working at the camera, even if I could not actually see the comets. I was counting on post processing to make them visible in the image.

The same day that the breakfast discussion had occurred, one of Howard Astronomical League’s dark observing sites was opened for its members, and I went out on my first attempt to image the three comets. I set up with my Canon 60Da mounted on a Omegon LX2 Mini (mechanical wind up) tracker. I had not used this device for some time, so I found myself fumbling with it way too long. By the time I was polar aligned, had the target framed, and decided on the exposure, I was exactly one hour later than I had hoped to start imaging. By then the comets were very low in the mucky part of the atmosphere, and ground fog had started to appear. I did not have a dew heater for the camera lens, so it was completely overwhelmed by moisture.

While still in the field, I was able to see NEOWISE in my unprocessed images on my dewy laptop screen, and I was able to verify that I was capturing the star field that contained the other two comets. Even though I could not see the comets in these images, I was hopeful that I would be able to pull them out in post-processing. My luck had run out. In processing the next morning, I found that I did not have a useable image of the three comets.

Amazingly, we had another lucky break in the clouds, and the site was opened again the next night night. I added a battery and dew heater to my pack up, and headed out again. Equally as important, I spent some time reacquainting myself with the tracker in the clear light of day. It was another very moist evening, but not nearly as challenging at the night before. Because I was not fumbling with the tracker, I was able get up and running and was shooting sub-frames as soon as it was dark enough. I could see right away that my data quality was much higher than the night before. I couldn’t see the other two comets, but I saw enough stars that I was pretty sure that I could pull the other two comets out in post processing.

Getting the image that I wanted out of the data that I had captured the night before required that I stretch my processing skills to the limit, but somehow I managed. Not only was I able to see the two dim comets, I cross checked against Stellarium to verify that the two green blobs were indeed Lemmon and PANSTARRS. Here is the Three Comets image that I posted to Flickr.

I must add that I am pretty impressed with the tracker. Of the fifty sub-frames that I shot, I threw away only one for a tracking issue. Not bad for a $200, low-tech wind up device?!!

Technical information for Three Comets: Canon EOS 60Da with 55mm lens at f/2.8, and mounted on a Omegon LX2 Mini Tracker. Twenty minutes total integration time in 47 x 25 second light frames. Calibration frames consisted of 25 dark frames, 25 flat frames, and 25 flat dark frames. Light frames and calibration frames were stacked in Deep Sky Stacker, and post-processing was done in Photoshop.

© 2020 Jim Johnson

Portable Power Solutions for Astronomers: Part 5, Conclusion

We have reached the end of a three-part series of articles on the power required to get an astronomer through a night of observing. We began by discussing battery types, distinguishing between a battery as but one component of a complete astronomy power solution, and then we identified the other components of this complete solution, which includes a case, outlets and their circuit protection, and a battery charger that will ensure that the battery is ready whenever it might be needed next.

At a high level, we found that battery usage can be defined in terms of a three-way trade space of battery capacity in amp hours, total amp load of the devices drawing power from the battery, and time that the device load can be sustained before the battery capacity is depleted. How the capacity and load relate to time is important because this is the basis for how the adequacy of a battery for a night of astronomy is assessed.

Next, we gave a similar treatment to replenishing the battery’s charge after a night’s use. We found a similar three-way trade space between capacity in amp hours, amperage supplied by the charger, and time. We distinguished between a straight battery charger and a smart charger and identified the advantages of a smart charger when it comes to preserving a battery’s useful life. And finally, we discussed the context for determining the adequacy of a charger, especially when there is limited time to recharge a battery for use on two consecutive nights.

And finally, we discussed some particulars regarding commercially available power solutions, and DIY power solutions. The DIY solutions require much more forethought to ensure that the end product produces the desired result, and we pointed out that some electrical skills and a sense of adventure on the part of the astronomer are required for going this route. But a big advantage that DIY solutions have over commercially available solutions, especially those involving higher battery capacities, is that the DIY solutions can be far less expensive for those who can do it.

We hoped that you have found this series informative, and useful as guide to the research that you may want to do in determining the amount of battery capacity is needed in your power solution, and in determining the correct charging capacity for your needs. And lastly, we hope that you have an appreciation for how commercially available units are alike, how they differ from DIY solutions, and for which might be the better route for you.

We would love to hear about your power solution, how you use it, and how it was decided. Helpful comments below are always appreciated.

© 2021 Jim Johnson and Doug Biernacki

Portable Power Solutions for Astronomers: Part 4, Other Considerations

Upon arriving in the field with a suite of astronomy gear that must be set up before nightfall, an astronomer has a lot of work to do, often in a short amount of time. The considerations discussed in this section are an essential part of how an astronomer gets the job done on time and how the job gets done correctly. These considerations apply to all the astronomer’s equipment, batteries included. And finally, as no battery lasts forever, we will close out this series of articles by discussing factors that can limit a battery’s useful life.

Before going into details, description of commonly encountered power solutions is in order. I use the term “solution” to avoid the names that commercial producers use for their battery equipment (like pack, tank, etc.), and because the specific power equipment that an astronomer selects specifically solves the astronomer’s power problem.

As discussed in Part 1, a complete power solution consists of battery itself, possibly a battery enclosure, possibly a monitoring device or devices, circuit protection for the outlet connections, the outlet connections and a battery charger. The battery is likely to be withing the enclosure, and all the other components are likely to affixed to the enclosure by means of a panel mount. The battery charger restores the battery’s charger, in a manner that preserves the battery’s useful life, and quickly enough that the battery is available the next time that it is needed.

As for the battery itself, all that was said about volts, amps, amp hours and charging in Parts 2 and 3 apply. A monitoring device is required to detect when the battery has reached is maximum safe discharge level so that the battery can be disconnected and not be damaged by being overly depleted. Sometimes a color-coded charger indicator serves this purpose. Circuit protection can be either a circuit breaker or a fuse that interrupts the circuit if a higher load than is anticipated is encountered, usually one for every outlet connector. The most common outlet connector accepts the cigarette lighter plug, but Anderson Powerpole connectors are becoming more common. The enclosure that contains the battery, and to which the other components are mounted, can take a wide variety of forms. Manufacturers’ enclosures are custom made. Trolling motor or other battery boxes are sometimes used by do-it-yourself (DIY) builders of power solutions.

There are four important considerations concerning battery use in the field: handling, setup, connecting, and use. The less time spent on placing the battery into service, the better, because there are so many other details to which the astronomer must attend before darkness arrives.

From a handling perspective, batteries are heavy and can be difficult to transport and handle in the field. Generally, the higher the capacity in amp hours, the heavier the battery. A carrying handle of some type is essential here, as it can allow many batteries to be carried with one hand, leaving the other hand open to carry some other gear. Commercially marketed solutions have handles or carrying straps. Most battery boxes that DIYers use have handles.

Having all of the components mounted on the enclosure helps not only by eliminating setup time, it also prevents polarity errors in connecting components and it prevents components from being forgotten or lost.

Getting polarity correct when connecting equipment is essential and should not be presumed to be as easy as it looks. If a connection can be made incorrectly, an astronomer in the field who is in a hurry can probably find a way to do it incorrectly. A red wire and a black wire, for instance, does not look the way one might expect when viewed under red lighting. The consequence of reversing polarity is the likelihood of damaging expensive equipment and ruining a night’s observing session.

During use, monitoring devices, at the very least a voltmeter is recommended. Most battery manufacturers will specify a minimum voltage to which a battery can be discharged to, and a voltmeter is required to monitor and avoid this situation. An ammeter can be helpful too, as it provides an indication of the rate that power is being used, which gives some estimation of long the battery will provide power before hitting the minimum safe voltage. Also, the astronomer will know if the load on the battery is heavier than it should be, in which case the anomaly can be corrected before the battery is prematurely exhausted.

And finally, a word about commercially available power solutions and one that is designed and assembled by the astronomer. Ultimately either type solution can provide the voltage and amp hours that are needed to get through a night of astronomy. And the principles of volts, amps, capacity and charging apply equally to both types as well, so choosing a solution that provides the needed capacity is critical in either case.

Where the two approaches differ most, however, is the DIY solution requires research to select components, and it could require some level of electrical skill and sense of adventure on the part of the astronomer. Other differences are that amp hour for amp hour, a solution that the astronomer builds will cost less than the commercially produced one. In the higher capacity solutions, the difference could be a couple of hundred dollars. Or alternatively, much more battery capacity can be obtained for the same amount money. And finally, with the DIY solution the type and quantity of connections desired by the astronomer can be built in to suit the astronomer’s needs.

Batteries do not last forever and have limited useful service lives that vary by battery type. What is more, there are factors that can shorten a battery’s expected service life. Over charging or over discharging a battery are chief among these factors. Keeping a battery on a maintenance charger can eliminate overcharging, and keep the battery properly charged for extended periods of time. Having a voltmeter as part of the power solution package permits the astronomer to monitor voltage and disconnect the battery before it becomes over depleted. And finally, being exposed to unmoderated high and low temperatures in a garage or outdoor shed can send a battery to an early demise.

Doug and Jim have both used commercially available power solutions but are transitioning to DIY solutions. Let us and others know about how you decided on your power solution by leaving comments below.

© 2021 Jim Johnson and Doug Biernacki

Portable Power Solutions for Astronomers: Part 3, Doing it Again Tomorrow Night

In Part 2 of this series, we examined the how battery capacity and total device current draw over time relate to having enough power to get through a night of astronomical observing. In this installment, let us assume that we had enough battery capacity and/or our devices did not draw too much power, and we just got through one great night astronomy adventure. But now our battery is depleted and requires recharging before it can be used again. First, we will examine some battery charging basics and then we will consider options for charging, including some ways to view charging relative to time. And finally, we will suggest a way to assess whether your charger can get your battery ready for tomorrow night, i.e., using the battery for a second consecutive night after a charging period during daylight hours.

Some batteries can accept higher charging rates than others, so care must be taken when selecting a battery charger. Also, AGM and Gel batteries must be recharged using a charger that has the capability of charging AGM and Gel batteries. There is no substitute for reading the instructions that came with your specific battery.

Battery charging is a function of the same factors as battery depletion: battery capacity, charging amps, and time. Charging amps is the opposite of amps that draw down a battery’s charge. These amps are electrons, or charge, flowing back into the battery. As the battery’s amp hour capacity increases, more charging amps and/or more time are required to restore the charge. No matter the capacity, more charging amps result in less charging time to restore a battery to a full charge.

Consider a 4 amp charger and a 2 amp charger connected to two identical batteries at identical levels of discharge. The 4 amp charger will fully restore the charge to a battery twice as fast, or in half the time as a 2 amp charger.

With the relationship between amps and time covered, lets now vary battery capacity. Keeping the charging amps constant and varying the battery capacity, a 4 amp charger will recharge a fully depleted 17 AH battery in roughly half the time that it takes to recharge a fully depleted 33 AH battery.

A battery charger, once connected to a battery, will begin applying a charging current to a battery as soon as the charger is powered on and connected to a battery. Unless the charger is manually disconnected from the battery once a full charge is reached, the continued application of electrical charge will eventually damage the battery. Once the charger is disconnected from the battery, the battery’s charge will begin to slowly dissipate over time. If a long time has passed since the battery was on a charger, the user might find that its charge has significantly diminished upon trying to use it. The counter to this might be to reconnect the battery to the charger for a period to top off its charge just before use.

There is a special kind of battery charger that is commonly referred to as a smart charger. Other terms are for this type of charger are maintenance charger or float charger. A battery is more easily maintained with a smart charger that is rated for that type of battery. Once connected to a battery that is at less than full charge, they work just like an ordinary battery charger. When the battery reaches full charge is where the special capabilities of a smart charger come into play. The charging current is automatically stopped by the charger, and it then goes into a monitoring mode. At this time, the battery’s charge will begin to slowly dissipate over time as any other battery does when removed from a charger. When the battery’s charge has depleted to some specified level (usually just a small amount of depletion), the smart charger will automatically cycle back on until the battery’s charge is once again topped off.

This cycle of charge-monitor-charge will repeat for as long as the smart charger is connected. It works much in the way that a home heating system thermostat keeps the room temperature within a narrow range. Smart chargers have the advantages of being healthier for the battery as they prevent the battery from damage that may be caused by either overly discharging, or damage from being on a charger too long. A practical advantage from a use perspective is that a smart charger ensures that the battery is always fully charged and ready for a night’s work, but that only works to a point…

But consider a multi-night regional star party scenario. Say that on the first night most of the battery’s usable capacity has been depleted. It must go on a charger to get ready for the next night. Ideally, the battery will be completely recharged during the daylight hours. Depending upon the amount of battery capacity that is to be restored, and the charging amperage available from the charger, the daylight hours of a single day might not be enough time to fully restore the charge.

If the amount of charge that is to be restored is accepted as a constant, and the amount of time available to recharge the battery is also a given, then the only way to speed up the process is to apply more charging amps. Smart chargers have amperage ratings that range from well under one amp and up to five amps (or more) are commonly available. If the astronomer needs to restore the charge to a large capacity battery in a single day, then the higher rated charger is likely to be required. On the other hand, if the astronomer does not anticipate ever using the battery for two consecutive nights, then a lower rated charger is likely to suffice.

A good place to start when assessing the adequacy of a battery charger’s recharge time for a specific battery is the battery charger manual. Most are available online and will contain a section that shows the amount of time that the charger will require to recharge a battery based on the amp hour capacity.

Much in the same way that battery life rehearsals were done at home in Part 2, we can do charging rehearsals as well. It is just a matter of keeping a log regarding battery capacity, charging amps, and time. Below is a sample battery charging log. Unlike the prior log where an entry was made each time the load on the battery changed, this log has one entry per charging event. Some monitoring of the charger status lights is required to identify when a smart charger transitions from the charging mode (which indicates that the battery if fully charged) to the maintenance mode. Also, this example assumes that the astronomer owns two batteries, and a log entry is made each time a battery is charged.

Battery Unique NameCharging AmpsStart Date/TimeStart VoltageStop Date/TimeEnd Voltage
Kendrick 33 AH2.755/23/2020 083011.85/23/2020 163013.2
Kendrick 18 AH.755/23/2020 083012.45/23/2020 131513.2
Kendrick 33 AH2.755/24/2020 074512.25/24/2020 154513.2
Kendrick 33 AH2.756/18/2020 070012.25/24/2020 150013.2

Now that we have covered batteries and battery charging, we can move to Part 4 and consider the entire power solution. Helpful comments below are welcome.

© 2021 Jim Johnson and Doug Biernacki

Portable Power Solutions for Astronomers: Part 2, Just One Night

This Part of the Series reviews battery types and then explores the question: what does it take, in terms of battery power to get though a night of astronomical observations? Not having enough power to get through a night’s observing plan can be a big disappointment considering the amount of effort required to field a telescope for a single night. The power that is required to get through a night, in short, is a function of the capacity of a battery that ideally exceeds the power needed by all the devices that are drawing power from the battery for the duration of an observing session.

There are many battery types, but deep cycle batteries are the choice of astronomers. Deep Cycle batteries allow for continuously supplying power for long periods of time.  They can also discharge more of their stored energy.   Deep cycle batteries are also constructed with thicker plates so they can withstand repeated charge and discharge cycles. 

Breaking it down further, there are different types of deep cycle batteries:  Flooded Lead-Acid (also called wet cell), Gel, absorbent glass mat (AGM) and Lithium.

The flooded lead-acid battery is the older of the designs.  For example, traditional marine and car batteries use flooded lead-acid batteries.  These batteries require maintenance involving keeping each of their cells filled with water, and cleaning terminals.  They must be kept upright and can be heavy.  However, they are less expensive than Gel and AGM (per amp hour cost).   

The Gel and AGM batteries incorporate improvements over the flood lead-acid batteries.  They do not have water cells which eliminates need to maintain water levels in cells.  The Gel batteries use an electrolyte Gel, and the AGM uses electrolyte absorbed in a fiberglass mat.  Their advantage is they will not release gases when charged.  They are sealed so they reduce spillage and do not have to remain upright.  They are lighter in weight.  They are more expensive than the flooded lead-acid battery. 

Lithium batteries are expensive, but they have many advantages.  They require no maintenance, can be discharged more deeply and are light weight.  They also provide more power throughout discharge cycle, and they are not damaged if operated or discharged at a lower level of discharge.

As for how a given battery gets an astronomer through a night, voltage is usually the first consideration on both sides of the equation as both the power source and the devices that it powers must have the same voltage rating. By far the most common battery used for astronomy in the field supplies 12 volts of direct current, or 12 vdc. Most astronomical equipment runs on this voltage, or other voltages are derived from the 12 vdc battery.

Derived voltages may be encountered on occasion. The Losmandy goto system, for instance, runs better on 18 vdc than 12 vdc, so a boost converter is used to get the higher voltage. Jim fields two of these systems.

Voltage is the amount of force or pressure available to create current flow. A battery’s voltage is measured with a voltmeter by placing leads on the positive and negative battery posts. Fully charged, a 12-volt battery’s actual charge will usually read around 13.2 volts. During use, a battery’s voltage drops as it is depleted toward some lower limit, which varies by battery type. It is also important to note that a battery’s charge will slowly begin to dissipate after it is removed from a battery charger, even though there are no powered devices attached to draw down the battery’s charge. Some batteries can dissipate their charge at up to 3% per month.

There is usually a specified lower limit to how far a specific battery can be drawn down. For instance, Kendricks specifies 11.6 vdc as the lower discharge level for the sealed batteries in their Power Packs. The lower limit varies by battery type and manufacturer. Drawing a battery below the recommended limit can damage the battery or limit its useful life. Reading the instructions that came with the battery is highly recommended.


Amperage (amps) comes into play as well. Amperage is a measure of how many electrons (how much charge) flows past a given point in a circuit per unit of time. Terms like current, load, and draw are used to describe the current that a device uses, or alternatively, at what rate and for how long a battery can supply power before being depleted.

Powered devices have a rating in amps that describes how much current flow is required to operate them. A dew heater strap at its highest temperature setting, for instance, is likely to draw more power (amps) than a small camera. Most astronomical device literature describes the maximum amps that a device might pull, but depending on the device’s state, it might be drawing a lot less power than specifications suggest. As an example, a mount control system might draw much less than an amp while the telescope is tracking at a low speed, which is most of the night, but it could draw well over an amp for several seconds while it is slewing at a high speed from one target to the next.

Knowing the actual amperage load of a of all the devices connected to a battery is important, because it is the total draw over time that depletes a battery’s charge. Knowing the battery’s capacity is also important because this determines how long a given load can be sustained before the battery’s charge is fully depleted.

Battery capacity is specified in amperage hours (amp hours, or AH). Many batteries will give their amp hour rating based on 20 hours of capacity based on an average amp draw per hour.  The formula to assess a draw against a battery is amps (summed for all the devices connected to the battery) multiplied by time.  For example, a 7 AH battery can sustain a draw of 1 amp for 7 hours, 7 amps for 1 hour, or some other tradeoff of amps and time in between.   

Most battery specifications will describe Amp Hours at 20 hours.   This translates into how many amps (or fraction of amps) can be drawn per hour from a battery for it last 20 hours.   For example, the 7 AH battery would last 20 hours while drawing .35 amps per hour.  So, if you are drawing .35 amp hours your battery lasts 20 hours.  If you use 1 amp per hour your battery will last 7 hours.  Hence, by knowing your power requirements in amp hours you can determine how long your battery will last using 20 hours as a benchmark. 

This kind of analysis could seemingly help an astronomer compare the total equipment suite’s load to battery capacity to assess sufficiency of the battery for a full night of observing, but it is difficult to perform because of several factors. On the powered accessory side of the equation, it is difficult to know the actual draw of each device as its operating state changes over the course of a night. On the battery side, cold weather and battery age could reduce capacity.

A way around this limitation is to conduct dress rehearsals at home. An astronomer could engage in a night’s observing, just as if the observing site were away from home. Avoid connecting anything that will be taken to the field to household current. Power up everything, to include dew heaters and the laptop as well. If an ammeter is available to measure the load in amps, then connect it as the first device on the positive side of the battery and take notes of the amps being drawn. Also take notes of the length of time that the equipment is powered up, and on the how the battery depletes over time during the night. Here is an example log:

Battery Unique Name: Kendrick 33AH
TimeEventBattery VoltageAmpsDuration (Min)
2030Equipment powered on13.22.9 
2100Battery check12.82.930
2115Dew heater on12.73.245
2200Battery check12.63.290
2245Battery check12.53.2135
Sample Battery Usage Log

A power log like the one above can provide valuable insight into how telescope, accessories, and battery perform as a system. The Battery Voltage is a voltmeter reading of the voltage present at the time of the log entry, and the Amps column is an ammeter reading of the total draw in amps that was. If the log suggests that the battery capacity is inadequate to power an observing session through the night, there are alternatives to consider: add battery capacity, reduce the load, or plan for less observing time.

Most astronomers have a lot to learn about powering their equipment in the field. If you have helpful information, please leave comments below regarding your battery performance experience.

© 2021 Jim Johnson and Doug Biernacki

Portable Power Solutions for Astronomers: Part 1, Overview

Bringing portable battery power in the field to run a telescope, mount, and other accessories is commonplace for many amateur astronomers. Many of these astronomers are content with the battery that they purchased along with their mount and telescope. Perhaps it has only powered the mount since it was purchased, and if that is likely to be the extent of its use into the future, then these astronomers may be content with an in-kind replacement of the original battery when the time comes for replacement.

As Give a Mouse a Telescope illustrates, there is always something else that most astronomers will need. A dew heater or two is added, then a camera or two (maybe one of the cameras is cooled), and maybe a focuser is added (and the list can go on and on), and soon the original battery becomes overwhelmed as it lacks the power required to get an astronomer though a full night of observing with the additional accessories.

Consider also that a battery has a limited life. As an old battery is being replaced, the astronomer replacing the battery has probably gained a greater appreciation of the range of future possibilities for his or her equipment. In this case the astronomer may want to consider a more capable power solution that can power not only the telescope and mount, but accessories that are likely to be added for future astronomical plans.

This series uses the term power solution instead of battery, as most packages that astronomers commonly refer to as “a battery” is comprised of several components that might include an enclosure for handling and protecting the battery. The enclosure may also provide panel-like surfaces for mounting other electrical components, which are likely to include some means for monitoring the battery’s voltage as it discharges, power outlets to which telescope accessories are connected, and circuit protection for the outlets. And finally, no power solution is complete without a battery charger that restores the battery’s charge after a night’s use.

Considerable attention will be paid to the battery component of the power solution because it is the most expensive component and specifying a suitable battery for a specific astronomer’s needs requires the most forethought. Most of the other components of a power solution could be the same for a given astronomer’s use case regardless of which battery that is chosen. Depending upon the battery capacity chosen and how quickly the astronomer wishes to have the battery fully recharged, the battery charger might need to scale up with the battery capacity. To be clear, a use case does not dictate the power solution; the astronomer’s power requirements and personal preferences and imagination will ultimately lead to the power solution that is chosen.

As The Astronomical Cost of a Mulligan reveals, not getting the replacement power solution (or any astronomical acquisition) right the first time can be expensive. This series of articles aims to provide some considerations to guide an astronomer’s research as replacement power solutions are explored, with the hope that the next power solution will be the right one the first time.

Safe battery depletion levels and battery charging rates are discussed in this series of articles to illuminate relationships between battery capacity, charging rates, and depletion levels.  Safe depletion levels and charging rates vary by battery type, so there is no substitute for reading the battery manufacturers literature on these subjects.

Toward this end, Part 2 of this series examines how the power requirements of the accessories that an astronomer anticipates using should be a factor in determining the right amount of battery capacity required to meet those power requirements. Once the battery is a known component of the power solution, then how the battery will be used and battery and charging considerations are addressed in Part 3. And finally, Part 4 examines some considerations that influence the selection of a commercially available power solution, or alternatively will influence a power solution design for a do-it-yourselfer.  

We hope that you find this series helpful. Please leave comments letting us and others know about your power solution and how you selected your components and the design.

© 2021 Jim Johnson and Doug Biernacki

The Astronomical Cost of a Mulligan

A mulligan in casual golf is taken when a player repeats a bad stroke without penalty in cases where the round’s participants agree to allowing a mulligan. The concept of a mulligan is often extended to include situations outside of the game where a second attempt is desired in order to supplant a less than desirable outcome after a first attempt. But often in life there is no mulligan at all, or if there is a do-over, it is not without penalty.

In purchasing astronomical equipment, there is often a temptation to select a less expensive and therefore less capable item than the one really desired in order to save money. As Give a Mouse a Telescope illustrates, astronomers’ satisfaction with such an item might be soon give way to the need for a similar but more expensive and more capable model. I will call this do-over an astronomical mulligan. Astronomical mulligans may be necessary or unnecessary, but as they can be expensive, they are best thought through before making a purchase that might require a do-over.

An extreme example of an astronomical mulligan that could have happened would be my thinking as I considered building an observatory several years ago. Initially, I thought that I would spec my observatory to support a 10” SCT refractor, which I thought would be plenty of capability for my needs. The 10” refractor would, after all, be quite a move up from my 4” refractor. The requirement to support and house the 10” telescope translated to a certain size concrete base in the ground, a certain size pier, and telescope mount of a certain capacity, and a certain building size. If I remember correctly, I could have pulled this off for about $25,000.

But I kept thinking, and I wondered if I would be happy with a 10” telescope forever, and if I should consider a 12” telescope. And my thinking eventually progressed to a 14”, and on to 16”. The specifications and the costs for the telescope, base, pier, mount and building do not scale linearly. In fact, they scale quite exponentially. My estimated price tag for an observatory based on a 16” telescope came to about $90,000! A ridiculous amount of money, so I ultimately elected to not build an observatory at all.

Now think if I had built the 10” version of the observatory, later became unhappy with it, and subsequently decided to build another version that would support a larger telescope. Assume in this case that I had skipped the 12” and 14” editions of the observatory and elected to go with the 16” version of the observatory. None of the five major components (base, pier, mount, building, or telescope) from the 10” observatory could be used in the 16” observatory. My costs would be $25K for the first observatory plus $90K for the observatory that I really wanted, for a grand total of $115K to get my forever observatory. This analysis would be much worse if I had built three observatories before finally arriving at the 16” version, never mind having to explain three or four observatories in the back yard to my wife.

My observatory considerations are an extreme and perhaps an iron clad example of when to think ahead in order to avoid a mulligan and make the “forever” acquisition up front instead of progressing through three acquisition iterations beforehand.

Sometimes planning for a mulligan can make sense. If just starting out in astrophotography, for instance, is going straight for the expensive full frame DSO forever camera at the outset a wise decision? Maybe it makes better sense to gauge one’s interest and capabilities by starting with a less capable DSO camera and declare the mulligan and buy the forever camera only if the experience with the first camera goes well.

From a value perspective, this might be a reasonable approach as there are value offsets to the cost of the first camera. The obvious one with dollar signs attached is being able to recover some of the money spent by selling the first camera after moving on to the forever camera. But perhaps of even greater value is the confidence gained before spending the big bucks on the full frame camera.

Astronomy is an expensive habit, excuse me, I meant hobby, even on a good night, so astronomers should strive to make cost effective purchases that meet their needs. Thinking through mulligan scenarios is a way to do this. To plan for or to avoid a mulligan are equally valid considerations that can help an astronomer make the best use of their astronomy dollars.

© 2021 Jim Johnson