At the end of my last post I mentioned a few things you should list in your logbook when observing open clusters so you could reference the information later and compare it to a more recent observation of the same object. That sparked an idea for this post and, as I thought more about it, I realized that it would be a good idea to start talking about keeping a logbook in general. I have kept observation logs since the early 1980’s and I’ll look back through them from time to time and recall some interesting things that happened while observing on a particular night or compare how improved my observing skills have become or even how improved telescopes have become since those early days as an backyard astronomer.
So, let me ask you this question; do you keep an observation logbook? I hope you answered yes to this question because it really does help you to become a better observer. Taking notes on what you see makes you really take a good look at the object in the eyepiece. Looking back on those early observing notes I noticed that I always described objects with the same few words like, “striking”, “great”, “bright” or “faint”. Okay for a first impression but not very descriptive about what I really saw. So, I decided I would start taking notes based on a few parameters. Over the coming weeks I’ll get into more detail about observing and logging double stars, star clusters (open and globular), nebulae and galaxies. But for now, I’ll start with what I call “Session Notes”. These are notes about the circumstances surrounding the night’s observations such as location, sky conditions, who, if anyone, is present with me and any personal notes I care to make about the night.
There are many ways to keep a logbook. I keep it relatively simple, my logbook is a wire bound book of sketch paper where I’m free to write anything I want and make a sketch if I feel so inclined.
At the top of the page I list the start time in local time and the date in double date format and I’ll convert to UTE at a later time. It typically looks like this:
Date: March 16/17 2014
Start Time: 9:35 PM EDT – End Time: (fill this in at the end of the night).
Next is the location where I’m observing from. Most of the time its right here at the 90 Millimeter Observatory but from time to time I’ll drive out to a dark sky location so I’ll make note of it here. You can use a physical description or latitude-longitude description. Use whatever works for you.
Telescope: If you have more than one telescope, it becomes important to make note of which one you’re using on this particular night. Looking back at a few older observations when I didn’t note the scope I was using I thought to myself, was that with the 90mm f/10 or the 120mm f/8.5? I could guess based on the magnification a particular eyepiece gave me but its just easier to make note of which telescope was being used.
Next is the NELM (Naked Eye Limiting Magnitude). This is the faintest magnitude star you can see without optical aid. Its best to wait until your eyes reach dark adaption to record this. If you need a chart to help you with the limiting magnitude, AstronomyLogs.com has a couple of downloadable charts that I have found to be very handy.
Now on to seeing, which is a scale noting how much the Earth’s atmosphere perturbs the images of stars. The scale is a five-point system with 1 being the best seeing and 5 being the worst seeing conditions. It’s easy and it goes like this:
(I.) Perfect seeing, without a quiver.
(II.) Slight quivering of the image with moments of calm lasting several seconds.
(III.) Moderate seeing with larger air tremors that blur the image.
(IV.) Poor seeing, constant troublesome undulations of the image.
(V.) Very bad seeing, hardly stable enough to allow a rough sketch to be made.
The last entry here is transparency. This is a measure of particles in the atmosphere affecting viewing conditions. I use the Saguaro Astronomy Club (SAC) scale. It’s a scale from 1 to 10 and goes like this:
0 completely cloudy, no stars seen (why are you out?)
1 more than 50% of the sky is cloudy
2 more than 25% of the sky is cloudy, less than 50%
3 more than 10% of the sky is cloudy, less than 25%
4 no clouds but hazy, only brightest stars seen down to 4th magnitude
5 somewhat hazy, some fainter stars seen, to mag 5;
Milky Way visible only in brighter regions
6 not visibly hazy but Milky Way visible only in brighter regions
(Sagittarius, Cygnus, Norma + Crux); stars seen to mag 5.8
7 fainter stars, equal to mag 6.0 are seen and the fainter parts of the
Milky Way seen with averted vision, Zodiacal light seen with averted vision
8 stars fainter than mag 6.0 are just seen and fainter parts of the Milky Way
are more obvious, Zodiacal light is seen with direct vision
9 stars fainter than mag 6.0 are seen with direct vision and so are faint portions of the Milky Way (Lyra, Libra), gegenschein seen with averted vision
10 overwhelming profusion of stars, Zodiacal light and the gegenschein form
Continuous band across the sky, the Milky Way is very wide and bright throughout
Finally I’ll add a few personal notes about the night in general like, how I feel, who, if anyone is there, any issues I’m having with equipment, etc. It may seem like a lot at first but by doing this initial step you give yourself time to dark adapt, time for the telescope to cool down and just relax for a few minutes be for settling down for a good night’s observing.
Next week I’ll talk about recording deep sky objects and what to look for in each type.