Observing Meteors Visually

Observing Meteors Visually 

Taken from BAA blog

Naked eye observation of meteors is one of the easiest and most pleasant forms of work open to the amateur astronomer. Even a beginner can make useful observations, and it is a good way to learn the constellations. Meteor work is excellent for clubs and societies with little or no equipment; essentially only the human eye is needed.

A meteor during the peak of the 2009 Leonid Meteor Shower. The photograph shows the meteor, afterglow, and wake as distinct components

The notes below assume that a single observer is on watch, though most of what is said is relevant to group observation. Organisation of a meteor watch by a group of observers is more complex, though potentially productive of much more useful data (see Group Gbserving below)

The first requirement for the observer is to find a good dark site. Rural residents are favoured here. Urban lights, smog and haze have a major, adverse, impact on meteor rates. Hence, even if you have to drive some miles to get to a good site, it will be well worth the trouble to have darker skies.

What equipment should I use?

1. Norton’s 2000.0 Star Atlas or similar star maps.

2. Report sheets (will be made available to you during the meteor observation).

3. Timepiece – accurate to better than 30 seconds. 

4. Dim red torch – to enable you to note down data, but retain the dark adaptation of your eyes.

5. Several pens or pencils. These have a habit of breaking or getting mislaid in the dark, so have plenty of back-ups!

6. Clothing. Bring plenty of this; even on a summer night it can get chilly, and it is better to have too much clothing than too little. One advantage of a house back-garden site is that one can retreat indoors to warm up if necessary. A hat reduces loss of body heat from the head.

7. Food and drink. Refreshments should be available to be taken during breaks. Alcoholic beverages should, of course, be avoided!

Observer requirements

are rather more stringent

1. Patience. This is the prime requirement. The observer may face long intervals between meteors, or waiting for clouds to pass. Eagerly-awaited shower maxima often appear to turn out cloudy, and observations may have to wait for another year. Remember, however, that observations are required on all possible nights during a shower – so don’t just restrict watches to maximum night. One advantage of group watches is that the company helps to pass cloudy intervals.

2. Alertness. You must always be alert, otherwise the fainter meteors, which generally make the bulk of the bag, will be missed. If you are tired, or cold, or find your attention wandering, you should stop observing, at least for a while, since your results will not be reliable.

3. Honesty. All observers have different eyesight, and perception for meteors. An observer must not be disappointed to see fewer meteors than a colleague. Meteor work is not a competition, and conscious or unconscious ‘doctoring’ of observations is worse than useless, and indeed misleading.

Observing

Having covered the instrumental and personal requirements, we can get down to what is required from the observations. Before going outside to observe, find the radiant co-ordinates for the shower(s) active on the night in question, in this case it would be in perseus.

It is important to note that the radiant position the night of peak activity only. In accordance with theory, radiants generally move among the stars at a rate of about 1 degree per day. So, for a night other than maximum, the radiant will have RA and Dec different from the values mentioned.

Plot this position in Norton’s, and draw a circle of 8 degrees diameter centred on this position. The enclosed area is taken as the radiant for the night in question. Examine this area carefully indoors, until you are confident that you will recognise the area in the sky when you actually begin to observe.

Once outdoors, use the time that you spend getting dark adapted to record your name, address, and observing site (including latitude and longitude), and date on the report sheet. Note the sky conditions, mentioning whether any cloud, moonlight, fog or mist is present. Once you are fully dark-adapted, estimate the magnitude, to the nearest 0.25 mag, of the faintest star you can see in the area of sky being watched (not the zenith). Some observers prefer to estimate this limiting magnitude using the North Polar Sequence.

Now you are ready to begin the watch. Write down the start time of the watch in UT to the nearest minute. All times used in this type of work are required in Universal Time, which is 5.5 hours + IST. 

Of course, because astronomers work exclusively at night, the date changes at midnight, halfway through the observing period. To prevent confusion and ambiguity as to exactly which night the observations are carried out, one must record the Double-Date on the report form – for example, 30-31 October.

Some observers, once they get past midnight, use the 24-hour clock beyond the figure 24 so that, for example, 2 am becomes 2600 UT. This is quite acceptable. So long as your record of date and time is unambiguous, do what you find most convenient.

As the name implies, a meteor watch involves concentrating on the sky and noting details of any meteors seen. Solo observers should watch the sky 50 degrees above the horizon, and 30-40 degrees to one side of the shower radiant expected to be active on the night in question; most meteors should be seen here.

As each meteor appears, not whether it was a shower member or a random sporadic, estimate how bright it was, and give its time of appearance to the nearest minute in UT.

To ascertain whether a meteor belonged to a given shower, or was a sporadic, mentally project its path in the sky backwards. If the projected path intersects the 8-degree radiant circle, the meteor is a shower member. Otherwise it is a sporadic. Those with paths tangential to the radiant should be considered as possible shower members. If a stick, or piece of string is held up against the meteor path when the event is seen, this will give you time to collect your thoughts after the meteor has vanished. Estimation of the magnitudes of shower and sporadic meteors may be omitted by those observers wishing only to carry out counts. The others should estimate meteor magnitudes by comparison with nearby stars. It will be adequate to estimate to the nearest whole magnitude. Do not forget that there is a mag. 0 between -1 and +1. Estimation of meteor magnitude is largely subjective, since the meteor is rarely present long enough to enable very accurate visual photometry; it is a remembered impression that is compared with the stars. For bright meteors, errors in magnitude estimation are much larger, due to the lack of suitable comparison standards. Useful tips for bright meteor estimation: Full Moon is mag. -12.5; Venus is -4.4 at its brightest; Jupiter about -2.2. Large scatter in the magnitude estimates of fireballs can hardly be avoided. The list here offers some further suitable comparisons for fainter meteors:

Magnitude Object(s)

-4 Venus

-2 Jupiter

-1 Sirius

0 Capella, Rigel, Arcturus

+1 Regulus, Spica, Pollux

+2 Belt stars of Orion, Beta Aurigae, Gamma Geminorum,
Pointers of Plough, Polaris, Denebola, Alphard

+3 Delta Ursae Majoris, Gamma and Delta Leonis, Epsilon Geminorum

+4 Eta Persei, Delta Aurigae, Rho Leonis

+5 Faintest meteors generally visible to naked eye

Note the time of appearance of the meteor, having made due allowance for the time spent thinking about magnitude and type, and writing these down, perhaps 15-30 seconds.

Then, and only then, you may make any notes about the meteor itself. For example, did it explode? Did it have an intense colour? Did it have a long-duration persistent train?

As this is the first time we have mentioned meteor trains, a few words about them would not go amiss. Many observers, especially beginners, are confused by the difference between meteor trails and persistent trains. A night-time meteor train appears as a faint nebulous streak of light left behind, along the track of a meteor, but AFTER the meteor itself has extinguished. Do not mistake it for the actual moving streak of a fast meteor – this is the trail. Momentary meteor trains are generally likened in appearance to the vapour wake of a jet aircraft, and are only left by about a quarter of all meteors. Meteor trains lasting more than a few seconds are quite rare. Statistically, one must observe about 600 meteors to observe a train of 10 seconds’ duration or more!

Each meteor seen during the watch should be treated similarly; practice makes perfect, and you should soon be able to get down the data quickly and efficiently. Abbreviations such as “S” for sporadic, or “P” for Perseid, and writing the minutes instead of minutes and hour, will help you to cope with the sudden rushes of meteors that sometimes occur. As long as you get all the data down, and you can understand your symbols at a later date, you can use any symbols you like. Many experienced observers, to reduce “dead time” spent looking away from the sky, note meteor details in such a shorthand, for later, neat transcription to the Section’s report forms.

At the end of the watch, note the time to the nearest minute. Then you can stop, or have a break and start another watch later. Ideally, watches should last for an hour, or multiples of an hour, at a time. Monitor the sky conditions during each watch, as these may change.