Visual Observations

Visual observing and the resulting “hourly rate” is still the basis of meteor astronomy. Despite the increasing use of photographic and video equipment, visual observations still provide an important function in the analysis of meteor rates. All newcomers to this field are encouraged to become proficient in visual observing before expanding their methods of obtaining meteor data.

There are several ways in which to observe. Many observers take paper and a clipboard outside and record data as it occurs. This has the advantage of reducing work after the watch as your data is already transcribed on paper. All you need to do to obtain totals and other calculations. On the negative side the observer needs to take their eyes off the sky to enter data in the field. This creates a loss of viewing time and a resulting loss of meteor activity. Some proficient observers have overcome this by using a roll of paper instead of a clipboard. They write without looking away from the sky and roll the paper with each entry to avoid transposing data on top of each entry. Most visual observers take some sort of audio recording device outside with them and recite the data which will be recorded on paper at a later time. It can be a long process listening to the recordings but the observer has not taken their eyes off the sky so no time or activity has been lost.

We ask potential visual observers to view meteor activity for at least 1 hour. This is the basic unit in meteor calculations. Rates and results are always listed in meteors per hour. Another reason for this request is that during major displays there are always peaks and valleys of meteor activity. Even during the strongest showers there can be 5 meteors occurring within one minute and then 5 minutes go by when nothing is seen. By observing for at least 60 minutes the observer will witness both periods of high and low activity. Thus the results will reflect a good sample of the overall activity during that particular period.

The most important item to record is the type of meteor seen, whether it be a shower member or a sporadic (random) meteor. Each shower has been assigned a 3 letter designation which can be used plus SPO for sporadic meteors. Usually, the exact time of each meteor appearance is not important. However, in periods of high activity it will be necessary to reduce the hourly rate into smaller increments such as 1 to 5 minute periods – thus time marks in respective sequence are required. The magnitude (brightness) of each meteor is also important to record. To the beginner, this is often difficult and will take many sessions to achieve a good degree of accuracy. Memorize the magnitudes of stars within your field of view and use them as reference. Depending on your sky conditions, the mean magnitude should be near +3.0. If it is +2.0 then you may be overestimating the brightness of each meteor. If your mean magnitude is +4.0 then you may be underestimating the brightness.

Another important factor is your limiting magnitude. This is basically the faintest star you can see that lies near the center of your field of view. This figure tells us the condition of your sky and allows us to adjust your results so that it may be directly compared to other observers. In days past an observer would take a chart of the sky outside that listed stellar magnitudes and find the faintest one they could see. Nowadays, the IMO has created areas in the sky where the observer simply counts the number of stars visible. The resulting number is compared to a chart which will list the equivalent limiting magnitude. It is advisable to use at least 2 and preferably 3 different areas as the limiting magnitude varies with elevation (distance above the horizon). Not only can the limiting magnitude vary with elevation, it can also vary over time so it is suggested that limiting magnitude estimates be taken at least once an hour. If viewing conditions change due to twilight, clouds/dust, moonlight or other effects, then limiting magnitude estimates should be taken more often.

As you gain experience in visual meteor observing, you can also begin recording other parameters of each meteor including velocity, color, and whether the meteor left a persistent train.

More information on visual observing can also be found in the Handbook for Meteor Observers.

You can also find more information on the IMO’s Visual Commission.