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The Astronomical Log Book

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So how long have you been into astronomy? Take a quiet moment and reflect back over your observing career. Do you remember the excitement of your very first telescope?, the first time you seen the glorious rings of Saturn?, and what about those spectacular aurora displays, meteor showers, fireballs, great comet, or that naked eye sunspot as the Sun set into the murky western sky late at the end of a gorgeous summer evening?. Better yet did you keep a written record of your observations?. Astronomy is not just about observing, it's an experience, a life style, but more than that it's a collection of priceless memories. I have been observing the night sky for over a decade now, however since 1997 I decided that I would start recording my observations in an astronomical log book, in hindsight this was one of the best decisions I ever made. At the time of writing I have began log book number six and just before Christmas last year I decided that I would read through each and every one of them.

The shock

To say that I was shocked would be an understatement. I felt very confident regarding my recollection of all the things which I have experienced in the night sky however that list in my head turned out to be but a leafless branch on a fully blossomed towering oak tree of observations and memories that I didn't even know existed, but which lurked deep within my subconscious unknown to me. Reading through my early penciled and penned words opened a gateway of astronomical and meteorological observations, delights which not only include my own catalogue of celestial objects, but which documented my own thoughts and feelings through time. I was surprised by just how much my observing programme has grown and evolved, but even more than that I was shocked by just how much I had grown and evolved as a person through that decade. My own personal philosophy to observing and to life as well as the people around me through that ten year journey staggers me, and if it were not for my records all of these up's and down's would have been lost forever. Since humans first looked at the stars they have kept records of the various transient phenomena which they have gazed upon with both astonishment and even fear. First on stone, then on paper throughout the ages. Things have changed little since then, we still observe the sky, we are still at awe with what it can reveal to us at any time without warning and so we must continue to document what we observe. It is our duty as self appointed watchmen and women of the sky.

Why Write This Article?

Atlas Check Thumbnail I have been in conversation with various amateur astronomers about this subject and many expressed their wish to start an observing log book of their own but never quite got around to it or knew how to begin. So it's with this in mind that I decided to write this article in the hope that I can encourage others to do the same. I hope some of you reading this now will begin to do so. I promise it will become a treasure trove of information for you as it has been for me. You wont regret it.....lets go!!

Getting Started

You can use whatever you like to record your observations...

Note Books

Individual A4 pages in a binder

If you know your way around a computer then why not store your records on the hard drive or onto disk, however always make sure to back up your data on a regular basis.

I'm sure you will come up with your own medium that suits your needs. I prefer to use the large annual day to day page diaries as they can hold an incredible amount of information. I personally prefer the written word compared to the computer as I can access its contents quickly, plus I find that staring at a computer monitor can be damaging to the sensitivity of my eyes and hampers my dark adaption. I always carry a small pocket-sized note book in my observing jacket where I can rapidly record information and sketches at the eyepiece when in the field. Later that night, or the next day, I would then transfer this information in a more neat and detailed manner in my log book from the comfort of indoors.

This is why many observers are put off as it can be very time consuming to do, however it need NOT be. If you make it a part of your daily routine then it will become second nature with practice. It's really up to you just how detailed you want your records to be, an entry can be only one or two lines long ,or it can full two pages..it's really up to you.

The Purpose Of The Log Book

Keep in mind that recording your observations serves two purposes.

1) The first is for your own use so that one day you can look back on your observing achievements. This is the sentimental part.

2) The second is for scientific reasons. You may never know when your observations will be needed by a third party such as a professional astronomer or researcher. Your detailed description of a fireball, your magnitude estimate of a variable star/comet or Nova could be very useful if there has been a gap in the data. Observations of an aurora can be important to an individual who is researching their frequency at a given latitude and time frame so please keep this in mind.


Try and update your latest observing session into your log book as soon as possible to maintain accuracy, plus the longer you leave it then the less chance there is of you doing it at all...remember observations locked away in your mind are not observations at all and are of no use to anyone including yourself.

What You Need To Include

You will need to record some if not all of the following information...

1) Time of the beginning and end of your observing session, or at the midpoint of your astronomical sketch. All times should be in Universal Time (UT) or at least your local time.

2) The double date, month, and year example: 9/10th July 2006.

3) Telescope type, focal length, focal ratio, eyepiece used, magnification, apparent FOV (field of view), plus you might also want to mention if you used a diagonal and comment on polar alignment and the accuracy of your motor drive or go-to encoders and drives if you have any. Keeping notes on your telescope's performance, modifications, upgrades' etc can be great to look back on.

4) Your target: give a detailed physical description of your astronomical target, this may also include a sketch or image you took.

5) Make a note of the local weather conditions. Include a transparency and seeing scale, percentage of cloud cover, the presence of any moon light, any mist, fog, murk, snow, high level cloud and so forth.

6) I try to always include my own thoughts and feelings during a session regarding my equipment, the sky, and how I'm feeling which adds that personal touch.

7) I always record my observing location whether it be the front or back garden, the country, or a specific area like when you are with your local astronomical society for an all night session. I also include the names of anyone I observe with, their scopes, and their own observing agenda, so I end up recording not just my own work but the work of others as well although this is not necessary of course.

8) Misc - It's the little things that make records of high sentimental value like keeping notes on what's happening in the environment around you. You might want to include nocturnal formations of Geese, any visits in the night from Foxes and other wildlife, any human visitors, heavy frosts, heavy sudden snow falls, gale force winds, lightning, light pollution, chimney smoke, area's of the sky blocked by trees and buildings, power failures, collimation trouble, car head lights, human noise, any personal things happening in your own life, the effects of work and other people on your observing time, future plans and purchases etc.

Advanced Observing

Log Book Pic 3 If you are involved in a specialized field or undertake your observing in a serious way then you NEED to record everything you do. Anyone who observes variable stars, hunts for Novae, Supernovae, Comets or astrophotography of any description needs to document the precise details of their work and camera equipment settings. When I search for comets I always include the constellation sections I sweep through, the names of the Messier, NGC, and IC objects swept up, any suspects that need to be checked out, sketch and describe any new objects I've never encountered before, comment on how systematic I am, if I'm sweeping too fast or too slow, how far I search from the sun, proximity to the ecliptic, the compass point in the sky, Moon phase and position, limiting naked eye magnitude, any internal reflections or ghost images in the FOV, light tress pass, any aeroplanes, helicopters, birds or insects which pass through the field, my

mind-set, mood, and health. I also record how many telescopic meteors and satellites I see, fireballs, auroras, Gegenschein, Zodiacal light, and any atmospheric phenomena I have noticed while comet hunting. Never forget to include any naked eye observations you make such as the brightness and structure of the Milky Way and any Messier objects seen without optical aid. Each of these different objects gets its own title and entry in my log book even when they are part of the same session.

Coding your Records

In order to save time you may want to code your notes. I code everything I do for this very reason. Use personal jargon, half words, numbers, and letters to aid this process. Naming telescopes also helps but remember to include a translation of your code system within your log book for others either at the front or back where it can easily be found. The following is an example from my own log book...

S/1768 E-M CHP 27/28.12.2005 23.30 - 00.56 LT (1hr 26mins) T7 57X SWA32mm B/Country CS/631

Translation: Tonight I began recorded observing session 1768 which began in the evening and ended in the morning from 11.30 to 00.56 local time on December 27th/28th 2005. I spent 1 hour 26 min's searching for comets (CHP stands for my comet hunt programme) with my 16" F/4.5 dobsonian reflector using a super wide angle 32mm 2" eyepiece at a magnification of 57X which I know has a FOV of over 1 degree (2 full Moon diameters). The session took place in my back garden, then afterwards in the country. It was comet sweep number 631. Then I go on to give a detailed written description of the session as outlined above.

Example 2...

S/1548 E-M NLC 2/3.7.2005 22.24 - 01.30 UT B8/NE/Camera H/B/P/S 4th Display

Translation: Recorded observing session 1548, an evening-morning session which took place from 22.24 to 01.30 Universal time on the 2nd/3rd of July 2005. I observed a Noctilucent cloud display that was present during this time period using 8X22mm binoculars, naked eye, and camera. I observed it from my bedroom window, back garden, a nearby football pitch, followed by a building site that allowed for a panoramic elevated view of the display. It was my 4th NLC display of the season. You can see that coding does help alot!


If you have been flirting with the idea of beginning an astronomical log book then I hope that this article has rekindled your enthusiasm for the project. As you can see it's a very worth while investment in your time and can only fuel and compliment your observing. In fact, I have been guilty of doing more observing on purpose just so I can have something else to include in my log, so it actually made me observe more!

On a personal level my own log books have been of incalculable value to me. Many times I have found a distant galaxy in the sky and may have been uncertain whether I had encountered it before or not, however because I numbered the pages and indexed my log books I was able to ascertain within min's if I had found that particular object before saving me valuable time. My log has also provided me with the material needed to compile my own observing statistics such as the number of comets, auroras, and Noctilucent cloud displays I have seen as well as the number of observing sessions I have completed with an accurate compilation of the hours I have spent searching for new comets. this information specifically tells me how much I have done for a given year or month including the least and most done one a single night.

Through my six log books I have been able to see a story emerge that not only documents my observing and own growth, but also variations in weather patterns from year to year as well as the slow but constant growth of light pollution in Maghera which I fear could end all observing from here in the future if the expansion rate keeps increasing without the introduction of light shields and new light pollution laws. I have learned that I get a significantly larger frequency of clear nights here than is forecast by the weather. On a typical moonless night the transparency is 8 or more out of 10 with stars to magnitude 6.5 visible on a nightly basis. I have also learned that we have the luxury of a significant number of aurora displays that often do not coincide with the charts showing that our latitude is quite favorable to sightings of the northern lights.

Thrills Of Starry Nights Past

I have experienced so many thrills and disappointments in astronomy over the years that I could not do them justice here but if it were not for my record keeping then I would have lost much of my most cherished memories under hundreds of nights spanning more than a decade. Here's a few examples...

Feb 2005. One of the most transparent nights I have ever seen. Vivid dust lanes visible in the Milky Way and stars to magnitude 7.0 visible with ease to the naked eye. That evening while comet hunting I found for the first time the Veil Nebula in Cygnus followed min's later by comet Encke. I said in my log book that evening that the sky was similar to what one must get in Arizona!

Dec 2002. I was undertaking a dusk till dawn Geminid meteor watch on a very cold frosty night when I seen countless spectacular fireballs before dawn. Two of them made me instinctively 'duck' while another left a glowing smoke trail in the sky 15 degrees long and visible for 15 minutes in the sky which was illuminated by the Moon..what a sight!

Aug 2000. After spending 8 hours searching for comets tonight (I had only begun 3 months earlier) I accidentally 'discovered' comet Encke extremely close to the Sun showing pink, red, and green colours!. This comet was picked up within the only clear strip of sky at the horizon as the rest of the sky was covered with a dense fog. This remains the most exciting thrill for me in astronomy.

Dec 1998. The early days, I got a 4.5" Tasco short tube reflector for Christmas. I loved it!! Must have spent a week indoors just looking at it when I should have been outside observing through it. My first light was M81 and M82 which instantly converted me to the deep sky for the rest of my life.

Aug 1997. I woke up late on this Summer night and decided to watch the stars from my bedroom window. Soon I seen bright unearthly blue search beams light up the northern sky blocking out the stars. I was blown away with the sight. I honestly thought it was the end of the world. After a little research the next day I realized I had just seen my very first aurora borealis display!

Final Thoughts

I can live through these experiences and hundreds more like them from a quick scan through these logs. These memories are more than priceless and every night a new memory is captured. When I'm of elderly edge I will be able to look back on these books, and the future books still to be compiled, and feel a great sense of pride. Astronomy is an amazing passion which can be very intimate, it forges your mind and opens doors to bigger and better places. Remember it's not just an observation you are recording tonight, it's also a part of yourself. I wish you every success and don't forget to email me with your own thoughts.

Martin McKenna

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