LogBook Basics

Observing Reports

The colourfull and detailed photographs we see of celestial objects are not at all like the ubiquitous "fuzzy blobs" we see at the eyepiece. Nevertheless you are freezing your buns off and loosing much needed sleep for work the next day so why not make a description of your observations that will make the huntworthwhile. Here are some suggestions to fill the empty spaces in your log book and to imprint the observing experience more deeply in your memory.

The Basics

The http://www.ocrasc.ca/ website has a downloadable log sheet template that is just super, but you can also make up one for yourself or customize the website version to your own needs. The main things to start your report should be the circumstances under which you observed:

Observing Location

Time (of observing session and of the observation of each object)

Optics (type of instrument, eyepiece, filters, power of magnification)

Transparency (page 61 of the RASC Observers Handbook)

Seeing (for me this is a subjective rating of the atmospheric stability based primarily on Planet features and double star observations)

To determine the magnification of individual eyepieces, divide the eyepiece-mm's into the focal length-mm's. So a 25mm eyepiece used in a telescope with a focal length of 1000mm would yield a magnification of 40x.

It is good to know the field of view (FOV)of each of your eyepieces in minutes of degree, then you can estimate the approximate size of the object. The sketch pad I use has the FOV for every eyepiece I use taped to the back, a handy reference. To calculate your field of view there are websites that will punch out the both the magnification and the FOV for most eyepieces, or you can do it yourself.

Place a star near the celestial equator just outside the field of view in the eyepiece so that as it drifts by in the eyepiece, with the motor drive off, if you have one. By timing the star's passage you can get a very accurate measurement of the actual field of view.

The earth turns 360o in 24 hours, so in one hour, the earth turns 15 degrees, that works out to 15'(minutes of degree) per minute. Now lets say that a star takes 2 minutes (120 seconds) from the time it enters the eyepiece field of view, passing through the center, until it disappears on the other side (t). We figure the field of view, (F) with the formula: F = t x 15

This gives us 1800", or if we divide this by 60, (60 seconds in a minute) we get 30', or 1/2o.

Lets try another example. If a star's passage takes 200 seconds, then we get: 200 x 15 = 3000" = 50' = .83o

It is also valuable to know the N-S-E-W directions of your FOV. For an undriven reflecting telescope West is the direction that objects drift towards and North is the counter clockwise direction from West. A description can begin by describing how you found the object, if you star hopped what pointer stars did you use? Did you see greater detail with averted vision? Or tube movement?

When describing the magnitude of any object I usually use a scale of:

Very Dim


Slightly bright

Moderately bright


Very Bright

Open Star Clusters

Some things to look for and make note of in your observing report:
a) What is the size of the cluster? (using the FOV measurements you have created)
b) Can you estimate the number of stars?
c) Are the stars of equal brightness? Or are most of them dim with a sprinkle of brighter stars etc.
d) Is there a pattern?
e) Are there many doubles or triples?
f) Is it loosely scattered or densely packed?
g) Are there any colourfull stars?

Globular Clusters

a) size?
b) bright or dim?
c) symmetrical (round) other features?
d) how close to the core can stars be resolved?
e) dense core?
f) gradual brightening to core or a distinct core with halo of faint stars?

Planetary Nebula

a) size?
b) shape?
c) colour?
d) features? (ringed, bi-polar, central star)


a) size
b) shape, N-S-E-W orientation if elongated?
c) the three main features of a galaxy are generally referred to as nucleus, a core and a disk,...how do they relate to each other?
d) magnitude, is it bright or dim?


In addition to the size, shape, brightness and colour descriptions you can spice it up a bit with some of these terms:

dense, loosely scattered, gradual or quickly or suddenly brightening, chains, arcs, packed, amorphous, dusty, milky, wispy, twinkle, elongated, extended, muted, subtle, hinted at, suspected, smudge, streak, compressed, concentrated, tendrils, gauzy, blob, clump, mottled, spikes, irregular, structure, rich (lots of stars), sparce (not many stars) condensed, ......tired, cold, hungry and satisfied.

There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.

Mark Twain (Life on the Mississippi)