Why Log?
 
An observation is lost if not recorded. An unrecorded observations exists only by what you can remember.
Through recorded observations it's easy to verify which objects you observed, what you saw, what equipment you used and what the conditions were at the time of the observation. When not recording observations objects often look familiar... Maybe because you are observing the same object again and again without realizing it?
Aside from that, logging creates you own, personal database: They are your observations the way you observed. That's nice for your own use, but it also allows observations of an object to be compared to those made by others. This can give new insight or bring further details to your attention, which will add to the enjoyment of observing. On top of that, amateur discoveries are still not ruled out!
 
Recording Observations
 
Recording observations starts behind the eyepiece. When I have an object in view I initially focus on the details of the object itself. Next, the surrounding starfield deserves attention. Bright stars in the vicinity may enhance the image you see, but may also function as a guide to the exact position of an object. Often there is more to be seen in the immediate vicinity. Two galaxies close together, for example, or a double star in the same field of view. Useful additions to an observation are patterns in the starfield; look for triangles, rectangles or trapeziums and describe where the object is in relation to these figures, or where it is part of it. Many stars have colors. Often subtle, sometimes striking. These details are all worth recording.
I count an observation when I have seen an object without any doubt, no matter how faint it is. I count double stars as an observation if I was able to split at least one component. "Combined objects", like open clusters in which a nebula is involved are counted as a single observation, just for ease.
I record my observations by using a voice recorder. This way I am not wasting time taking notes and I don't have to fiddle around with a piece of paper in the dark. I upload the files on the recorder to my laptop to work out my observations at a later time.

In addition to a description of an observed object I also note the atmospheric conditions, light pollution, wind and temperature. All of these factors contribute to a complete database of your own observations in differing conditions. Before my first observation and throughout the night I measure the SQM value. The value a Sky Quality Meter measures is a good indication of the conditions. The worse the transparency and/or the more light pollution there is, the lower the value will be. To keep this data unbiased I always measure towards the zenith (straight up), no matter the atmospheric conditions or the location of the object I observe. I apply no correction for the Milky Way or other factors. The Milky Way is no opaque band of light and applying a standard correction for this will result in a value that will not reflect actual conditions. The measured SQM is what it reads, and that's what I note.
 
Object Details
 
Although objects can be similar an observation differs for every object in combination with the equipment used, the observing site and the atmospheric conditions. Below are a few examples of things you can pay attention to while observing, per object category. Click on the objects' titles to read more on Wikipedia.

The images below are, unless stated otherwise, courtesy of Robert Gendler and are used with permission.
Click on a picture to view the original image on his site.
 
Open clusters
 
Open clusters can be rich or poor, concentrated or spread out. They can be detached or can be part of the surrounding star field. The stars can be of equal magnitude or can greatly vary in brightness. The colors of the stars can differ and quite often double stars can be discerned within an open cluster. Does the cluster have an even concentration of stars, or are 'holes in the cluster' visible? Is it round is does it have a different shape? Are there stars forming arcs or extensions? Is a haze of unresolved stars visible in the background, and do these stars resolve when using averted vision? Also, when observing open clusters look for nebulosity associated with some of them.
 
Globular clusters
 
Contrary to open cluster most globular clusters have one thing in common: almost all of them are round. The difference between them is mainly in the cluster's size, brightness and in the concentration of stars. Is the cluster uniform in brightness or is a brighter central part visible? Is the cluster well resolved and is there an even concentration of stars? Do significantly brighter stars jump into view? Is the cluster perfectly round, or perhaps oblong or flattened?
A higher magnification often works well on these objects. The background will be darker and, as stars are point sources, fainter ones will be visible. Using averted vision it is possible to see even more stars and further resolve the cluster.
 
Nebulae
 
Nebulae are difficult objects. Except for the well know, large, bright nebulae most are faint and difficult to observe... not what you would expect after seeing many of the beautiful pictures taken of them!
The problem when it comes to observing nebulae is the generally low surface brightness. Remember, the magnitude of a nebula may be low, but this brightness may be "smeared out" over a large area. Know which nebulae are within reach of your telescope and know what to look for. Filter (such as a UHC) may help but do expect any miracles. The effect is often subtle.
When you have a nebula in view note the shape, brightness and its size. Is the nebula uniform in brightness? Is structure visible? Dark spots? Detached parts? Is the nebula surrounding a star, as is often the case with reflection nebulae? What is the effect of a filter or the use of a different magnification?
 
Dark nebulae
 
These objects are a different breed. Dark nebulae consist of the same matter as emission and reflection nebulae do, but are not glowing or illuminated by stars. This makes them, both visually and photographically, dark interruptions of the star field. And that's exactly what you are looking for. Find the transition from an area with many stars to one were there are few or none. Knowing you are looking a the right spot try to determine the shape of such a dark area: Elongated, round or even meandering? Whatever it is, there where you are not seeing anything, there is the nebula. Not seeing something is seeing, in this case. Strange but true.
A telescope with a relatively large field of view using a low magnification usually works best to distinguish dark nebulae.
 
Planetary nebulae
 
Picture courtesy of Robert Gendler, used with permission (www.robgendlerastropics.com)Planetary nebulae come in many sizes and shapes. Large to small, round or uniquely shaped, sometimes extremely small and bright.
Except for the relatively large and bright planetary nebulae it is important to be looking at exactly the right locations to be able to observe it. For large, faint nebulae to observe the faint glow, which may not be apparent immediately. When it comes to very small nebulae it is often impossible to quickly discern them from the surrounding stars. It's not without reason that many planetary nebulae are described as 'stellar'. To be able to know with certainty which 'star' in the field is the nebula, you can try to use averted vision to see which of them appear to increase in size. A filter, preferably an OIII can be helpful as well. This type of filter is transparent only to light in the part of the spectrum the nebula emits. Using it stars seem to disappear while one gets brighter... that one is the nebula. A useful technique is "blinking": Alternatively viewing the same are with and without a filter, thereby looking for the nebula to reveal itself.
Some planetary nebulae have a visible ring-shape. A higher magnification is often useful to make it visible. Is the nebula uniform in brightness, or brighter towards the center? Is the central star visible? Contrary to other deepsky objects (unless observed with a really large telescope) something else may be visible in planetary nebulae: Color! Not always as apparent and often subtle, but tints such as light green or turquoise are often visible.
 
Supernova remnants
 
Picture courtesy of Robert Gendler, used with permission (www.robgendlerastropics.com)Only a few of these special objects are visible through amateur telescopes. SNR's resemble nebulae, but are of course a different type of object. That's why filters have very little effect, or none at all.
 
Galaxies
 
The vast majority of the visible deepsky objects are galaxies. Literally thousands can be seen through amateur telescopes. They come in all shapes and sizes. Small and large, round or elongated, extremely faint or very bright. A few are visible to the naked eye under good conditions, the faintest are a challenge to observe.
The first thing which is notable when observing a galaxy is its shape. Very often a galaxy is no more than a gray smudge or a small, faint smear in your eyepiece. Sometimes detail is visible, like spiral arms, dark lanes or a bright nucleus. Generally galaxies are brighter towards the center with a gradual transition from the outer halo to the core or a very abrupt one instead. The central part can be round or elongated in the same direction as the galaxy as a whole. Other galaxies are duller and uniform in brightness without further detail.
Averted vision helps greatly in discovering more detail in galaxies. A faint nucleus can become visible, or a dark part, or even a satellite galaxy that initially remained undetected.
For elongated galaxies it is useful to know the PA (position angle) in advance, which is the angle the galaxy has with respect to north. By knowing this angle you will be able to determine how the galaxy is orientated in your eyepiece, assuming you know where north is. As with nebulae the magnitude of a galaxy can be misleading. The surface brightness is much lower for galaxies of above average size, thereby reducing the overall brightness of the object.
 
Double stars
 
Copyright 2005 Richard Yandrick, used with permission.
Everyone using a telescope sees double stars, but not all observe them.
Double stars a special category for many astronomers. Some want to view as many a possible while others try to use the smallest possible aperature to split the components. Splitting double stars is usually the goal when observing them. Apart from that many observe them for the striking colors that some double stars display.
A double star has a number of components, the brightest star usually referred to as "A'. The position of the other stars (B, C, etc.) is noted by the angle of the stars in reference to A and north. This angle is known as PA (position angle), the distance as "separation" (in arc seconds). To be able to determine this angle it is essential to know the directions in your eyepiece. Without knowing exactly where to look it is nearly impossible to split components which are either very faint or have a minimal separation, or both.
Using a higher magnification makes fainter components visible and enables you to to split components with a smaller separation.
When observing double stars look for color contrast. Ask yourself the simple question: "Is component A white?". If not, what color or tint is it? Do the other components have exactly the same color? By observing double stars in this manner you will notice that quite a lot of color is present.
 
Carbon stars
 
Image courtesy of Al Kelly, used with permission.
Carbon stars a nice to observe for their striking colors: Ranging from bright orange to deep red. Exceptional to see every time. Carbon stars are variable stars, therefore their brightness varies and, with their brightness, the color. The closer the star is to its minimum, the deeper red it will be. The brighter, the more it will lean to orange.
 
Asterisms
 
Asterisms are not true objects. They are patterns in the stars, or groups of stars mistakenly identified as an open cluster. Asterisms which form a striking pattern are often assigned a fitting name, only because the first observer to note them recognized this shape or pattern. Falsely identified objects often keep their catolog name. That's why, for example, the NGC catalog contains countless asterisms.
 
Saving Detailed Observations
 
I transfer the observations stored on my memorecorder to AstroPlanner in text. This is the same program I use to plan my observations. AstroPlanner enables me to work out observations in detail and can provide additional information about an object when I need it. Not only of the object itself but about the everything visible in the immediate vicinity.
The details I record are, along with the date and time of the observation, the location and equipment used as well as the environmentals and relevant information about the atmosphere. Such as seeing, transparency and limiting magnitude. The amount of light pollution at your site, interfering moonlight or other matters that were of influence are all worth mentioning.
Page updated: 17 June 2010
Keeping track of observations and taking detailed notes of an objects is what I refer to as "logging". A collection of logged objects is in essence your personal astronomical journal. This page describes how I put this to practice.