Keeping an Naked-eye Observing Diary
This post is aimed at people taking my annual Winter Night Sky and Spring Night Sky astronomy classes held at Glasgow Science Centre, and organised by the University of Glasgow. However you might find it useful even if you aren’t taking that class.
Amateur and professional astronomers keep detailed observing logs whenever they use their telescopes or binoculars to observe astronomical objects.
Many new astronomers however will be satisfied with naked-eye stargazing to begin with, before taking the big step and buying a telescope, and even for complete novices an observing diary of some kind can come in useful to help you learn your way around the sky.
In this short post I will outline some of the key things to record in a naked-eye observing log.
Time and Date
All records should include the time and date of your observation. In order to keep this in line with other astronomers’ records, you should note the start and end time of your session in UT (Universal Time). Fortunately for stargazers in the UK, UT is the same as GMT the time on our clocks over the winter months. During the Summer, when our clocks go forward our time is GMT+1, so we need to subtract an hour from our local time to get UT. You should record this time as accurately as possible by setting your watch to the pips before observing.
You date should be in a double-date format, i.e 27/28 November 2010, indicating that you were observing on the evening of 27 Nov, and possibly into the morning of 28 Nov.
Describe the site you’re observing from in as much detail as possible, ideally with your longitude and latitude, but at the very least by postcode. Describe also how clear your view of the sky is and whether any parts of your view are obscured by buildings, streetlights etc .
What You Observed and Where it Was
Your should describe in as much detail as you can your observation of astronomical objects, e.g. which constellations you observed, the nebulae that you saw (maybe the Andromeda Galaxy, or the Seven Sisters), any planets etc. Describe the relative positions of these objects in the sky, as well as which direction you observed them in (e.g. N, SSE, SW etc) and how high above the horizon they were (remember this easy method for measuring height of objects in degrees).
The Observing Conditions – Weather
You should note the weather conditions throughout your observing session, and how it changes, specifically the cloud cover. Estimate how much of the sky, if any, is obscured by cloud. You normally wouldn’t bother observing if a significant fraction of the sky is covered. Note also temperature and air pressure (using your own thermometer and barometer, or taking the data from a reliable local weather station).
The Observing Conditions – Sky Quality
You will most likely be observing skies that are affected by light pollution in some way, and so you should note the limits imposed by this nuisance. Estimating your limiting magnitude is a little bit tricky, but certainly worthwhile learning how to do. Astronomers would note this in terms of what magnitude of star was the faintest object visible to you. There is a relatively simple method to do just this using the stars in Orion. You can learn how to do this on the GLOBE at Night website.
You should also note whether the moon was in the sky, what phase it was in, and how high above the horizon it was. When the moon is more than half full it produces natural light pollution that imposes a limiting magnitude on the faintest objects you can see.