Visual Observing of Meteors.
On this page you will find information on the following topics:
What you need to observe meteors
Where you can observe meteors from
Some things to know and learn before observing
How to make the observations
What do you need to observe ?
Meteor observing does not require expensive optical equipment. All that is required is a keen observer, a suitable site, and a few essentials to ensure the observer's bodily comfort. A checklist of items that are regularly taken on observing trips is useful when preparing for the trip, and avoids the possibility of leaving important equipment behind. Essential equipment includes:
- WARM CLOTHING: Prolonged observing requires the observer to remain warm. A warm coat, hat, scarf, and gloves are desirable.
- OBSERVING SEAT: A good resting place, such as a reclining lawn-chair or a groundsheet with a foam underlay, is necessary for the observer to remain comfortable. A warm sleeping bag will provide comfort on cold nights. Summer months require the use of bug repellent to keep the observer free from insect bites.
- ILLUMINATION: A dull red torch is required for illumination without ruining night vision. Layers of red bits from plastic supermarket bags, or a few layers of red cellophane, held over the top of a suitable torch will provide even illumination of the proper red colour. The brightness may be varied according to the observer's liking, but should not be too bright or it will interfere with the observations of others (as they are likely to tell you if your torch is too bright!).
- STATIONERY: Paper, pens or pencils, and observing forms are required to record meteor data accurately. This Observer's Kit is also valuable in the field, as it provides the necessary information to record an observation. Beware of the effects of dew which will ruin exposed papers! A vinyl clipboard can be useful in keeping papers covered.
- SNACKS AND DRINKS: Snacks and drinks are useful to keep an observer warm and free from hunger. Comfort is important. Oh yes!!! Observing strength coffee may be used to keep oneself awake in the early morning. It is easy to fall asleep when you think you are observing meteors!
- GOOD COMPANY ! It is great to be able to observe with a group of friends who share a similar interest in meteor astronomy. Our section has many trips with usually 2 - 5 people. It makes the night a lot of fun with some great conversations and stories while observing.
Where do you observe meteors ?
Meteor observing may be undertaken from almost any location. Over half the observing done by amateur meteor observers is done from suburban or city viewing conditions. To observe meteors under the best conditions, however, a dark sky site, free from interference of street lights and other pollution, is required. A site which is known to be reliable for cloudless conditions free from haze, fog, and harsh extremes of temperature is desirable. A clear horizon is also required, but a 360° clear view is not essential, since the field of view of the human eye is limited to 120° at most.
Sites which include the desirable attributes listed above are located far from the city of Melbourne in order to get away from light pollution. Sites on the Northern side of the Dividing Range provide good observing locations. Successful observations have been made from a site near Murchison in central Victoria. This site has a clear dark sky, free from heavy light pollution, and has a reasonably reliable climate. However, ground fog has a tendency to affect this site, and in serious cases may bring about the end of an observing session. The ASV Leon Mow Dark Sky Site at Heathcote is also suitable for meteor observing, possessing a dark sky and little light pollution (Bendigo produces a glow at the horizon towards the west which refuses to set!). The site does not have a 360° clear horizon due to trees towards the South. However, these trees may used to the observer's advantage, stopping winds which may produce an uncomfortable wind chill.
Before you start observing.
Estimating the Limiting Magnitude of the Sky
The darkness and transparency of the sky at an observing site determines whether faint stars and meteors can be seen. The magnitude of the faintest star visible is termed the limiting magnitude. Accurate calculation of this parameter is vital. The simplest method that observers have employed involves the use of an accurate star chart, with stellar magnitudes marked, of the observed part of the sky. The observer then compares the view he/she sees in comparison to the map view. The observer first picks out the brightest stars and then progressively tries to locate the fainter ones. The faintest star visible in the field gives an indication to the limiting magnitude. Most reliable results are obtained from averaging the limiting magnitudes from several visible star fields. Maps with magnitudes marked are included for this purpose. You will find these maps in Appendix F “Limiting Magnitude Charts” For areas which lie low on the horizon, the following corrections for atmospheric absorption are listed. Areas for estimating limiting magnitudes are chosen for those which are high up on the horizon and preferably in the direction the observer wishes to face.
Altitude of Centre of Region Atmospheric Correction, in magnitudes
50° or more 0
The atmospheric correction is added to the limiting magnitude. Quote all limiting magnitudes to an accuracy of 1 decimal place. For example, if an observer can see a 6.1 magnitude star but cannot locate the next star at 6.3 magnitude, the limiting magnitude is the average of the two values, 6.2.
Other items to note
There are other things to note before you start the observing session which are important. These include:
Visibility of the Moon
If any of your observing field is obscured by trees, buildings, etc
These can be listed in the comments section of your form, or in the appropriate sections. Items like Cloud Cover, and field obscurations are normally listed as percentages of the sky.
How is the observation carried out ?
The observation of meteors by visual methods makes up the bulk of amateur meteor observing. Below are outlined the procedures, used and adhered to by members of the ASV Meteor Section, which have proved successful in the past. The following sections describe the various levels at which meteor data can be gathered. Simple observations are recommended for the beginner, while more advanced observations should be undertaken when enough experience has been gained to make such observations of reliable value.
(a) Seeing a Meteor: A meteor can be said to be seen if its path can be accurately traced across the sky by the observer. Meteors appear as streaks of light of varying magnitudes of brightness and colours. The length, speed, and position of the streak across the sky are also characteristic of particular types of meteor.
(b) Recording Data : (See reporting page) The accurate recording of data is the most important part of observing. Basic data about observations must always be recorded, preferably before the commencement of an observing session. This should include:
* Observer's Name, age, whether spectacles worn
* Location of Site
* Date, and start and finish time of observation (Australian Eastern Standard Time, or state time zone clearly)
* Direction of Observation
* Percentage of Field of View covered by cloud or obstructions
* Limiting Magnitude (See section under this heading)
* Other sky conditions of relevance such as fog, haze, the presence of the Moon, and light pollution.
* Amount of obstruction in the observers field of view caused by houses, trees, etc
* If observing was done in a group, the names of the other observers in the group
* The recording method used
This information must be recorded with EVERY observation to ensure validity. There are forms for this which are used widely. Follow the highlighted text above for a view andexplanation of the form.
(c) The Characteristics of an Observed Meteor: They type of a meteor is uniquely defined by its characteristics as it is observed across the sky. These characteristics include:
* Brightness (Magnitude)
* Path across the sky
* Presence of a train and its duration
* Duration of visibility of the meteor
* Whether it explodes
* Bursts of brightness along the path
Not all of these characteristics can be recorded for an event which may last for only a second, but as many as possible should be noted and recorded in observations.
(d) Recording Techniques: Meteor information may be recorded in a number of ways. Observations may be written down or recorded on tape. Tape observations are useful as they keep the observer's eyes on the sky, but take care to protect the tape recorder from the effects of dew, and ensure that its batteries are fresh enough to perform well in cold conditions. Plotting meteor paths generally requires the observer to take his/her eyes off the sky, and tape methods of describing a meteor path are inadequate.
The various "schedules" of meteor observing are ordered in relative degree of difficulty according to observer experience, and are described now in more detail.
Meteor frequency observations
This is the simplest type of observation. Record all the information listed in section (b) ("Recording Data") above at the beginning of EACH hour, since some conditions may alter. Then, the number of meteors seen during a particular time period is noted. As each meteor is seen, a mark or note is made, similar to a tally. Meteor observations are done in statistically significant blocks of one hour. At the end of each hour the number of meteors seen is summed and recorded.
Magnitude, Colour, and Train observations
This schedule of observations requires the observer to record the following characteristics of a meteor IN ADDITION to that of the above meteor frequency observation.
Magnitude: The magnitude of an observed meteor is recorded to the nearest whole number. An observed meteor is compared to the brightness of a star of known magnitude. For this purpose a list of stars of various magnitudes is given later.
Colour: The colour of a meteor is noted in addition to its brightness. The bulk of all meteors are white. Observed meteors are categorised into the following colours of the spectrum: red, orange, yellow, green, blue, violet, plus white. Colours of meteors give an insight into their chemical composition.
Train: If a luminous linear glow (a train) is left after the bright streak of the meteor has passed, it is recorded as a train meteor. The number of meteors possessing trains is counted at the end of an observing hour. Train duration (how long before it fades out) should be recorded for an advanced observation.
The following shorthand method for recording the above data is recommended. When a meteor is seen in the sky, the observer compares its brightness with that of a known star to deduce its magnitude, there are charts in Appendix D for this purpose Its colour is also noted, and whether it had a train and if so, for how long the train persisted. Thus, for example, a third magnitude red meteor with no train would be recorded as: 3 r and a second magnitude yellow meteor with a train lasting five seconds would be recorded as: 2 y t5
Data may be recorded in this form down a column on a sheet of paper for each hour of observation. The respective form is filled by counting the number of meteors which fall into the categories of magnitude and colour. The number of meteors seen is counted and entered onto the form as is the number of trains seen.
Another way involves a meteor form designed for field use. The attributes of an observed meteor are recorded into columns of a suitable form. Such a form is included for this purpose.
Stream Frequency Observations
This involves the classification of meteors into sporadic and specific stream categories. The data recorded is IN ADDITION to that listed in the above observation. Observations of this type require a knowledge of the night sky, a thorough familiarity with meteor observing, and also require preparation beforehand to be able to identify the radiant of a meteor shower with respect to the stars.
Radiants are listed as an Appendix to this Kit and are given in terms of right ascension and declination which may be plotted onto a star chart and used to familiarise oneself with the radiants above the horizon at a particular date. Radiants have periods of maximum activity which are also listed. Once all active radiants are identified in the sky, observed meteors are traced backwards in their path of flight to see if they lie within about three degrees of a known radiant. Meteors which cross a meteor radiant DO NOT belong to that stream. Projection backwards to about 10 times the path length of the meteor is allowed.
Meteors which fit more than one radiant are divided between those streams, and fractions of meteors belonging to a radiant are counted. Meteors are classed into streams, and the magnitude/colour/train data is recorded for each meteor. Meteors which do not fit any stream are termed sporadic, and are listed under this category. The information gleaned from stream frequency observations gives insight into the streams' character.