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.
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.
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.
Kendrick 33 AH
Kendrick 18 AH
Kendrick 33 AH
Kendrick 33 AH
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.
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
Equipment powered on
Dew heater on
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.
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.
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.
If you give a mouse a telescope, he’s going want to collect photons.
When he collects some photons and realizes that the photons are not forming an image, he’s probably going to ask for an eyepiece. And then he’ll realize that he needs a tripod and mount to hold his telescope steady.
Now that he has a clear image, he’ll want to see more objects, so he will probably ask for a goto system. He’ll find more objects than ever with his goto system. He might get carried away and search for every object in the Messier catalog. He may even end up observing all of the objects in the NGC catalog as well.
After he’s been out all night observing these wonders, he’ll probably want a warm place from which to observe. You’ll have to build an observatory for him. He’ll crawl in, make himself comfortable, and clean his optics a few times.
He’ll probably ask you to read him a story about the Moon and planets. So you’ll read to him from one of your books and he’ll ask to see the pictures. When he looks at the pictures, he’ll get so excited that he’ll want to make some of his own.
He’ll ask for a for a nice camera and start capturing sub frames for a stacked image. When the sub frames are finished, he’ll want to process them with Photoshop or Pixinsight. Then he’ll want to post his picture online, which means that he will need a Flickr or Cloudy Nights account.
He’ll post his stacked image, and stand back and look at it, and realize that his pictures do not have enough detail. It occurs to him that more aperture and focal length are a way to make this better.
Chances are, he’s going to want a bigger telescope.
Bottom line up front, at this point I have no idea if I photographed 2I/Borisov, (the comet, hereafter) or not.
Here’s what I have to go on so far. The first image depicts a Stellarium rendering of the star field in which the comet was located when I imaged it this morning. Its computed location is indicated with a red X.
Next is an actual telescopic image from this morning. It is annotated to guide the reader through this discussion.
The frame scale and orientation are almost exactly the same for both the Stellarium rendering, and this morning’s photograph. Also in both images are green lines that highlight groupings of stars I used to determine that I had at least photographed the star field that should contain the comet.
In the actual photograph, I have placed a red circle in approximately the same relative location that the Stellarium rendering expects the comet to be, but I cannot see anything in this location.
I have also circled in blue two objects in the photograph that are not in the Stellarium rendering, and that are brighter than I expect the comet to be. I believe that these two objects are not stars, because I have done a lot of detailed comparisons between Stellarium renderings and actual photographs of the same star field. I have never found Stellarium to miss a star.
But I cannot say that they are the comet. That there are two unidentified objects instead of one in the photograph is suspicious.
Their brightness is suspicious too. The comet is projected to be 15.6 magnitude. Keeping in mind that a larger number equates to a dimmer object this would be a very dim object, even if it were a star. But comets are diffuse objects, not pinpoint objects like a star. This means that a comet’s reflected light is spread out over a wider area than a star, thus making it appear dimmer than a star of the same magnitude.
In the annotated photograph, I marked the magnitudes of three reference stars in orange. All three of these stars are of a lower (brighter) magnitude than the comet is projected to be, but even so, two of these three stars appear dimmer than the two circled objects. The third (11.2 magnitude), suggests that both of the unexplained objects in the blue circle are roughly 11th magnitude.
As I confessed at the beginning of this article, I do not know if I captured Borisov or not, but I have some guesses. One thing that could account for the separation between the blue circle (actual location of something), and the red circle for the computed location is that cometary data are updated periodically, and perhaps a future update will provide a more accurate computed location that places them within the blue circle. Another possible scenario that I would assess as highly unlikely, is that the comet broke into two pieces, and all of the freshly exposed ices caused the comet to flare up in brightness. Still not probable is that the flare up pushed the comet off of its original path, thus creating the discrepancy between the blue and red circles.
I will keep an eye out for news and cometary data updates for the next few days and report any new findings.
At about 1327 CDT on August 21, 2017 near Gordonsville TN, I stood less than 100 yards off of the center of the path of totality, waiting for the moon’s shadow as it raced across the earth’s surface, and I stood within that shadow for about two minutes and 39 seconds. A combination of many things put me in that time and place. Perhaps luck, skill, and drive were among them. Many have asked me to describe the experience, and my first words have included the word “beautiful”, and something like “words cannot describe. This article will be of few and inadequate words.
Astonishment is the single word that is probably most descriptive of my reaction. I had read a lot about eclipses, and I thought that I knew what to expect. Nonetheless, I was completely astonished at how quickly and how deeply the final darkness set in from the time that I could last see stark shadows on the ground, and then no shadow at all. The reappearance of light and shadows at the end of totality happened equally as fast. I was astonished at how bright and how large the sun’s corona appeared, and equally astonished at how vastly black and empty the moon appeared at the center of the corona. Gazing upon the combined effect felt to me as if a hole had opened up in the fabric of the universe. I actually felt a moment of panic.
I did manage to see Venus and Jupiter. I looked for, but could not see Mars nor Mercury. I could see parts of the “360 degree sunset” anywhere that I had a clear view of the distant horizon.
I made an effort to observe a phenomena called earthshine, where sunlight falling on the earth’s surface is reflected up to the moon, and back to the earth again. As I said before, I was astonished at how utterly black the moon appeared at the center of the sun’s rather bright corona.
I tried to observe the approaching umbral shadow of the moon, but could only see indirect evidence of it as light changed in and on the distant clouds. I also tried to view shadow bands against a white shirt that I had dropped onto the ground – nothing there either. All in all, no big deal.
I did not think to try to observe prominences on the sun. This is understandable as I had just lost my mind.
I visually observed first contact, the first bite that the moon took out of the sun, through a filtered telescope. I took peeks at it off and on in this manner, and with eclipse shades for the 90 minutes from first contact to totality. I did not observe anything after third contact when the sun emerged from the other side of the moon’s disk.
I managed to see the diamond ring effect just prior to totality and just after totality. I did not see anything that I could identify as Baily’s Beads.
I was able to observe solar crescents resulting from the pinhole effect of leaves in a tree just prior to totality. I noticed that the quality of the light changed, and shadows appeared to sharpen. And certainly, I could feel the sun’s intensity drop from early in the partial phase of the eclipse.
I did not notice any animals, so no behavioral changes were noted.
Secondarily to the eclipse, I devised an automated method of taking some images prior to and during totality. I clicked a Start button, and did not have to fiddle with the camera/telescope until after the imaging run was complete. Some preliminary, pre-processed images follow below.
The first image is of the diamond ring that appears in the final seconds before totality. In addition to the brilliant diamond, there are some features of interest to note in this photo. All three regions of the sun’s atmosphere can be seen. The white area from the reddish area just above the diamond to the reddish area just below the diamond is the photosphere. This region of the atmosphere is closest to the sun’s surface, and the white light that we observe from the sun originates here. The chromosphere is the next highest region of the sun’s atmosphere. It can be seen in the two reddish areas previously mentioned. Also, at about 2:30 and 4:30, promeninces rising out of the chromosphere can be seen. And finally, everything else, and the bright parts of the other two images are the outer region of the corona, which is the main event for a total eclipse of the sun. A final, processed image will be available shortly.
My travel plan was to arrive at Louisville, KY on the day before the trip, assess the weather, and choose an observing location on the morning of the eclipse. This reduced my risk of being locked into a location that would be clouded out on the day of the eclipse. Gordonsville TN was the location that I choose and drove to that morning. They skies had been crystal clear all day but cumulus clouds rolled in just as the moon’s disk began to cover the sun. Since there was enough clear skies between the clouds, and they were moving along at a pretty good clip, I felt confident that I would be able to get a glimpse of totality, if not see all of it. As it turned out, the sky became crystal clear again before totality arrived.
The entirety of the driving was arduous, and I put a lot of effort into planning for the trip. In short, it was well worth the effort, and I will put myself in the path of the moon’s shadow at every opportunity. The next total eclipse of the sun occurs on April 8th, 2024, just a little over six years from now. I encourage everyone to plan to travel to the path of totality to see this astonishing event.
The title of this article is a concise and precise definition of the ecliptic, but further explanation is warranted. Before delving in, I recommend reviewing the definition of a conceptual celestial sphere and reading Understanding a Star Chart to prepare for the material presented in this article. Although the ecliptic is an important aspect of lunar and planetary observations, and seasons on the Earth, this article will concentrate on the Sun’s movement among the stars, and how that movement defines the ecliptic.
As the Earth proceeds through its annual journey in its orbit about the Sun, the Sun’s position among the background stars, as seen from Earth changes a little each day. Since we intuitively know that the Sun outshines all of the stars in the sky, so this seemingly makes no sense. But imagine the Sun as a disk no brighter than the Moon. We could then see the Sun and the “fixed” stars on the celestial sphere at the same time, and we could track the Sun’s movements among the stars on a day to day basis. In a year’s time after beginning this exercise, the Sun will have returned to the point at which it started and we will have traced out the full course of the ecliptic across the celestial sphere. The twelve constellations through which the Sun traverses during this annual journey are known as the zodiacal constellations.
The Sun in the preceding image is in a fixed position for the purpose of this discussion. The Earth orbits the Sun as indicated by the blue circle with dates indicating progress through one orbit over the course of a year. Consider the Earth’s position on the blue circle on March 21st. When viewed from the Earth on this date, the Sun appears in the constellation of Pisces. Now consider the Earth’s position six months later on September 21st, and trace a line from the Earth through the Sun to see that it would appear in the constellation of Virgo.
The specific line that the Sun seems to trace among the fixed stars on the celestial sphere as a result of Earth’s orbit about the Sun is called the ecliptic, and is indicated by the horizontally oriented sine wave on the flat projection map of the entire celestial sphere below. This is a great place to start an exploration of the ecliptic. This particular map is a scan of the actual constellation map carried aboard the Apollo 11 lunar expedition. First, let’s become familiar with this map.
The horizontal lines are representations of degrees of declination, with 0° declination, or the equator across the center of the page, and the north (+90° declination) and south poles (-90° declination) are at the top and bottom edges of the page, respectively. Note that the vertical lines representing hours of right ascension do not converge at the poles (top and bottom edges of the map), because this is a flat projection.
To more closely relate the flat projection map to the celestial sphere, note that the zero hour of right ascension on the right edge of the map and the 24th hour on the left edge of the map are one and the same, so the right and left edges of the map can be brought together with the observer in the imaginary center of the map tube that is formed. The implication of this is that if one’s point of gaze slips off of the left edge of the map at, say +40° declination, the point of gaze would immediately appear on the right edge at +40° declination.
Compare this map to the sky map that follows below, and that was discussed in Understanding a Star Chart. The sky maps are contained within a circle that represents the horizon, and the stars contained therein are the stars that can be seen above the horizon at a specific point in time. The Apollo 11 flat projection, however, represents the entire celestial sphere. The ecliptic on the sky map below is designated by the yellow horizontal line that stretches from east to west, just north of the equator.
Let’s trace the ecliptic on the sky map below and compare the various aspects discussed with the Apollo 11 constellation chart above. Begin at the western horizon, where at that point the ecliptic lies south of the equator. Moving eastward (toward the left) along the ecliptic, notice that it crosses the equator (0°) at 0 hours (0h) of right ascension in the constellation of Pisces. At 6 hours of right ascension (6h), the ecliptic reaches its farthest distance north of the equator in Gemini, at which point it begin converging on the equator again just below the eastern horizon at 12h. Note that the ecliptic transverses several zodiacal constellations on this map. From west to east, they are: Pisces, Aries, Taurus, Gemini, Cancer, and Leo.
Now we are ready for a more thorough exploration of the ecliptic, which presents as a sine wave on the annotated Apollo 11 map below.
The Sun’s journey from one end of the ecliptic to the other, or from the right edge of the map to the left edge of the map, is exactly one year, then the cycle repeats. There are four very important points through which the Sun passes in its annual journey across the ecliptic. The two points at which the ecliptic intersects the equator (0h and 12h) are called equinox, and the points at which the ecliptic reach its farthest declination from the equator (6h and 18h) are called solstice. Let’s step through the Sun’s journey across the ecliptic as presented by starting at the left edge of the map.
1. The Sun’s arrival at the 0-hour of right ascension, or the intersection of the ecliptic and the celestial equator (0° declination), occurs around March 21st. This is known as the Vernal Equinox, or the beginning of astronomical spring. On the date of the equinox, the length of the day and the length of the night are about equal. Astronomical spring extends three months from this date while the Sun travels toward the intersection of the 6th hour of right ascension and +23° declination.
2. The Sun’s arrival at the 6th hour of right ascension coincides with it’s northern most declination of +23°. This point is known as the Summer Solstice, and it occurs around June 21st, marking the first day of astronomical summer. Astronomical summer extends for three months past this date as the Sun descends southward back toward the intersection of the ecliptic and the celestial equator at the 12th hour of right ascension.
3. The Autumnal Equinox is marked by the Sun’s arrival at the 12th hour of right ascension as it makes its south bound crossing of the celestial equator. This occurs on about September 21st each year, and is known as the first day of astronomical fall, which endures for three more months until the Sun reaches its southern most point on the ecliptic. For the second time in a year, the days and nights are of about equal length while the Sun is on or near the celestial equator.
4. The Winter Solstice is marked by the Sun’s arrival at the 18th hour of right ascension, and its most southward point on the ecliptic at -23° declination, on about December 21st each year. This is known as the astronomical beginning of Winter, which endures for the next three months as the Sun ascends northward toward the celestial equator.
As noted while describing the Sun’s travels from one edge of the map to the other, it also changes travels northward and then southward in declination from the equator reaching an maximum of +23° declination and -23° declination. This ±23° change of declination is related to the tilt of the Earth’s axis relative to the ecliptic, or the plane of the solar system, and this north and south movement of the sun is related to our four seasons on Earth. This topic will be addressed more thoroughly in The Ecliptic and the Four Seasons. The planets “wanderings” among the fixed stars is also related to the ecliptic, and this topic will be addressed more thoroughly in The Ecliptic and the Motions of the Planets. Look for these two articles in the coming months.