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Hints & Tips for Meteor Observers

 

Contents

 

Introduction

Although the SPA Meteor Section's webpages contain much information and advice on meteor observing generally, putting that into practice in the field inevitably raises questions sometimes, as to why certain things should be done in one way, not another, while the physical realities of observing create opportunities for ideas to make meteor watching a little easier. This page presents an eclectic collection of such items, many of which are intended to assist those with as yet little practical experience of meteor work.

Much of the material here was originally available on this website under the heading of "Shelagh's Spots", named after our Assistant Director Shelagh Godwin. Shelagh has been visually observing meteors with the Section since April 1987. When she became Assistant Meteor Director in September 1994, she took on responsibility for enrolling all new Section members. The extra contacts this brought, coupled with her own extensive observing experience, prompted the preparation of a series of short articles for the regular Meteor Section News Circular (NC) columns, beginning in NC 184 for February 1995, which were named "Shelagh's Spots". They quickly became a popular feature of the columns, and in 2000, a compilation of those already published was prepared, to enable people without access to the previous Circulars to still benefit from the advice. A revised version suitable for this electronic format featured from quite early in the life of the SPA's website, and as part of the major reorganization of the Section's webpages in 2009, it was possible to move some of the advice elsewhere on the site, without drawing the same attention to it as before. Not all of the information could be so readily transferred, so we decided to retain it separately here, and to expand it with additional notes, plus links to topics in the SPA's Electronic News Bulletins (ENBs) and on the Forums.

You may find it helpful to have a copy of the Section's instruction booklet Observing Meteors available when reading through parts of this page. If you have ideas for other topics not included here already, please contact the Director via meteor@popastro.com. Good luck for all your observing, and clear skies!

Beginners' Notes

Starting Out

If your New Year resolutions included taking up meteor observing, you may not find it too easy to keep this one, as the best showers tend to occur during the latter half of the year. A particularly good time to begin your meteor-watching career is near a major shower maximum, like the Perseids in August (always a favourite time, because of school and college holidays, perhaps with a trip away to a good, dark-sky site).

Allow yourself plenty of rest first, since you will see very little if you are exhausted, and then wrap yourself up warm and get out there, even if it is only for a short time initially. The small hours of the morning will be the best time for seeing meteors and avoiding neighbours' lights. You will find that you grow to love the peace and quiet and night sounds after the last trains have gone.

Seeing your first meteor can be very exciting indeed, particularly if it happens to be a fireball (any meteor of magnitude -3 or brighter, at least as bright as the planet Jupiter at its best). In that case, you should report it to the Section straight away.

Staying Awake & Alert

When meteors are not very plentiful, staying awake and focused on meteor watching can be a problem. So, to combat those drooping eyelids:

  • Try to get some rest during the previous day if you can.
  • Do not eat a large meal or drink alcohol before observing.
  • Ensure you will be warm enough.
  • If you are a "snacker", equip yourself with appropriate food and drink (a bottle with a straw or a drinking-nozzle cap is preferable to a glass or mug which might fall over or spill).
  • Do not stay in the same position for too long. On a lengthy watch, take a break, get up and walk around, shift your chair to help you follow the best field of view, observe a satellite or two, or some variable stars before returning to meteors.
  • Keep your mind alert by visually checking on other things in the sky.
  • In your head, compose letters you have been meaning to write, or a tune, or poetry, or have a stock of literature you have already memorised and can recite to yourself.

If you find you need your sleep and cannot catnap during the day, try observing in short bursts, say 2-3 hours each clearer night. To make the most of when you can observe, remember that for many showers and the sporadic background, best activity is in the small hours well after midnight (the Geminids, which are easily visible nearly all night, are a lovely exception to this). There is no point at all in observing if you are exhausted (but it's amazing how seeing a bright fireball can wake you up!).

When observing, don't stare at one part of the sky for too long. If you do, your eyes will get 'bored', and everything will become grey. If this happens, shift your position or get up and take a break, and remember to move your eyes around more. You might also try closing your eyes briefly, but be careful you don't fall asleep when outdoors, since even on an apparently not-too cold night, that may lead quickly to very serious problems such as hypothermia.

Sky Transparency

The sky is "clear", but how clear? Here is a rough-and-ready guide to sky transparency. Within 5-10 minutes of going outside, can you see:

  • All year round: The curve of three stars leading from Polaris to β UMi?
  • Autumn and winter: The four stars of the Y-shaped "Water Jar" asterism in Aquarius; the Andromeda Galaxy (M31); the three stars in the "Kids" asterism in Auriga?
  • Spring and summer: The three stars of Leo's back - γ, δ and 60 Leonis; the four chief stars of the diamond-shaped Lyra asterism; the four main stars of the Corvus asterism?

If you can see these magnitude +4 or fainter objects within 5 to 10 minutes, it is worthwhile considering a meteor watch, bearing in mind that it will take you up to 40 minutes to become fully dark-adapted. If you cannot see them - save up on sleep for the next really clear night!

When is Best to Observe?

You can see meteors on any night of the year, but the better times are during one of the major annual showers:

  • Early January - Quadrantids
  • Mid-April - Lyrids
  • Mid August - Perseids
  • Mid October - Orionids
  • Mid November - Leonids
  • Mid December - Geminids

Note that the names of the meteor showers listed here are taken from the names of the constellations from which the meteors appear to be coming. (The Quadrantids appear to come from an old constellation, the Wall Quadrant, which covered the area of the heavens now claimed by northern Boötes.)

Do not be tempted to restrict your observing just to times when the major shower maxima are due, however. Fireballs in the past have been observed quite frequently during February, a month when meteor activity is generally thought to be very low!

Observing Tips

Estimating a Second

When making fireball timings, or the length of time a persistent train is left behind after the meteor has passed, it's important to know what a second is. A couple of suggestions to enable you to look at the meteor instead of your watch:

  • Memorise a broadcast time signal. One of the best places to find this regularly is before the hourly news on BBC Radio 4. Each 'pip' is a second apart.
  • Practise using a clock or watch that reliably keeps good time, and that has a second hand or a seconds display on it, until you can count up to 10 seconds or more accurately without looking at the clock-face. You should find that counting "one thousand, two thousand, three thousand", etc., at a steady speed will help.

Dead Time

Inevitably when observing, you will not be able to watch the sky the whole time. You may need to take a break, and you may need to look at your watch after each meteor and note down details of what you saw. While you can usefully practise writing without looking down at your pad, for example, you should always be prepared to make an allowance in your watch duration for such "dead time". For typical visual observing, it's likely you'll have to allow up to five minutes dead time for every hour you observe.

Cloud Cover

Clouds can seriously affect your observed meteor rates, but you don't have to wait until the sky is 100% clear before you contemplate a meteor watch. You need to do two things. Estimate the area of sky you are observing that has clouds covering it, and every 15 minutes or so, note down this estimate as a percentage. This will enable your observed rate to be properly corrected when computing the Zenithal Hourly Rate (ZHR).

If the cloud cover grows to become more than 20-25% and doesn't improve before the next quarter-hourly estimate, the ZHR's cloud-correction factor will be too large to be reliable, so that is the time to think about a break for that drink of hot cocoa. If there is some clearer sky than this elsewhere, you can always shift your gaze to that area, rather than give up, because you need to estimate the percentage of your field of view that is cloud-obscured, not how much cloud there is across the whole sky.

Picking the Wrong Night?

Don't take shower peak predictions - even SPA ones - too literally. In 1998, a spectacular, early peak with many Leonid fireballs, happened the night before the maximum that year had been predicted, and quite a few people missed it entirely as a result. If your sky is clear, and the shower radiant is 20°-30° or more above the horizon, you could see reasonable to very good rates up to 48 hours before, and sometimes after, the peak of quite a few major showers. Whatever you do, don't "save" your observing until the peak if conditions are right beforehand!

Finding a Radiant

Radiant positions for meteor showers are given in the Meteor Showers List for the current year, and charts are provided for some showers in the Section's monthly meteor notes pages, showing how the radiants drift across the sky from night to night. It's essential to know where any shower radiants are for the nights on which you're observing, to tell which meteors might be members of a particular shower, or might be sporadics instead. If you have problems memorising the sky-location for radiants, perhaps especially when there are quite a number active simultaneously, such as in July-August, take a copy of the radiant charts out with you, suitably protected against the cold and damp in one or more clear plastic wallets, for instance. Take a few minutes to find each radiant area in the sky from your charts, and refer to them again during your meteor watch if you need to.

Shower Association

The angle at which the Earth approaches a meteoroid stream affects the speed at which these meteoroids enter the Earth's atmosphere and 'burn-up' as meteors. A point-source or short-pathed meteor travels straight towards the observer and appears to be moving more slowly than a longer-pathed meteor of the same shower travelling across the observer's field of vision.

So what does this mean for the observer? It can be very difficult to determine which shower a meteor belongs to, simply by trying to establish the radiant by prolonging the meteor's path back in a straight, imaginary line. In the summer months especially, there can be clusters of active radiants quite close to each other. Plotting the meteors onto gnomonic charts and associating each meteor with its more probable shower only after the watch helps, but isn't usually sufficient.

Using the apparent velocity as well can provide further help in shower association, especially in conjunction with the meteor's path length, and its distance from the radiant. The Meteor Section uses a 0-5 meteor-speed scale, where 0 = stationary or point-source, 1 = very slow, 2 = slow, 3 = medium speed, 4 = fast, 5 = very fast. This allows us to distinguish between a swift Orionid and a slow Taurid in October, for example. Very slow to slow meteors have velocities between roughly 11-30 km/sec, while fast to very fast meteors are around 55-72 km/sec.

Meteors have shorter apparent paths the closer they are to their own radiant. A long-pathed meteor crossing over a known radiant thus cannot have come from that radiant. In general, where the radiant is at least 25°-30° above the horizon, a useful guide is to assume that a meteor from a particular shower must have a path-length which is no more than half the distance back towards its radiant from its start point. In other words, the meteor's path must have started at least twice its own length from the radiant to be considered a member of that shower.

Observing While Ill

The major shower of the moment is upon us, and you cannot observe it because you're holed-up inside with a cold or flu. All is not lost! Wrap up warmly, and station yourself by a large window, suitably insulated against draughts. Pick a window where you can see plenty of unobstructed sky, ideally centred about 40° to 50° from the shower's radiant. If the shower lives up to its reputation, you might be pleasantly surprised at what you can still see even under such less-than-ideal circumstances.

Moonlit Observing

We advise observers to meteor watch chiefly when there is no Moon, because the brighter the sky, the fewer meteors will still be visible. About every third year, any given shower maximum will fall quite close to full Moon, thus making it unfavourable for observations. However, the stronger annual meteor showers, including the Quadrantids, Perseids and Geminids, can produce ZHRs of 100 or more near their peak, a level of activity that means quite healthy numbers of brighter meteors should still be obvious in clearer skies close to even a moonlit maximum. Other showers may produce lesser activity, but from a theoretical peak, which will need to be checked-upon despite any bright Moon, to help improve our knowledge of the shower's behaviour.

In such cases, the keen observer can still make a valuable contribution to our knowledge by keeping watch as usual, but in a direction looking as far from the Moon as possible, while still observing as much clear sky as comfortably practical. Hiding the Moon entirely behind a convenient rooftop, fence, wall or tree, will help as well.

Archived ENB & Forum Notes

Fireballs:

  • Separating satellites from fireballs: Forum.
  • Separating "sky lanterns" from fireballs: ENB 228.
  • Sundog mistaken for a fireball, 2007 February 1, Leeds: ENB 216.

Meteor Showers:

  • Identifying possible new minor showers from sporadics: ENB 229.

Meteor Observing:

  • Activity variations overnight: Forum.
  • All-sky fireball camera: Forum.
    Limiting magnitude determination: Forum.
    Point-source meteors and brief flashes of light in the sky: Forum.

Variations in Meteor Activity

You were expecting to see lots of meteors on your watch, yet saw only a few. Why could this be? Perhaps you were not watching at a time close enough to a shower's peak. Some showers, like the Quadrantids or the rarely-strong α Monocerotids, have a very narrow peak, so if you are not observing at that time, you are going to miss it. Others, like the η Aquarids or Orionids, have a much "flatter" maximum stretching over several nights. On nights well before and after a shower's maximum, you can expect to see very few meteors from that shower in any case.

If you wish to see a lot of shower meteors, it's best to wait until the radiant is high in the sky. Easily-seen meteor trails tend to begin at about 40° (a distance of sky covered by a 30 cm ruler held out at arm's length) from the radiant. A low radiant means that at least half the meteors will occur beneath the horizon and out of sight. Once the radiant has risen to about 60° above the horizon, a well-placed observer should be able to see meteor trails extending away from the radiant in all directions. Unfortunately for sleepyheads, this usually happens well after midnight, or even close to dawn, when sporadic rates also tend to be at their highest.

Why is it that in the frosts of February and March you tend to see very few meteors, even towards the end of the night? There are few showers active then in the northern hemisphere, and sporadic activity is at its lowest. Rates begin to pick up with the Lyrids and η Aquarids in April-May. In July-August you could be spending lots of time plotting radiants before you even go outside. Antihelions, Aquarids, Capricornids, Cygnids, there's no end to it, and then the Perseids too. None of them must be missed. There's a good spread of major showers, one each month, between October and January, and plenty of sporadics then as well. However, do try to observe on clear nights during February and March - as you never know what might happen.

Unexpected Meteor Showers

You're out one night and you see lots of meteors you didn't expect. It happened to some of us in 1998, when the June Boötids put on an unexpected show for the first time since 1927. If you see a sudden shower of meteors (even if you are not doing an official watch) try to note and report the following:

  • The date, time and place of the observation.
  • The sky conditions (clouds, limiting magnitude).
  • The approximate positions in the sky of the meteors, and note particularly if most of them seemed to have paths that came from one place (if so, please say as precisely as you can where that might have been).
  • The approximate speed of each meteor (fast, medium, slow).
  • The time of each meteor.
  • The brightness of each meteor.

If you cannot note down details for every meteor, give an approximation of the numbers you saw, and how long you were observing, preferably with exact start and end times.

Will It Be Clear?

Amateur astronomers spend much of their planning time with this question in their minds. For meteor watchers, the key event is often when a big shower maximum is coming up, so the important period will be overnight, and perhaps for just a few critical, often after-midnight, hours. Publicly-available weather forecasts in the media and on the Internet can be of limited help over such a restricted interval.

Some tips on interpreting the forecast. The best chance of a clear, transparent sky in Britain is just after a vigorous cold front has passed over, in the wake of a depression. Areas of high pressure which hang around for too long can result in hazy, stagnant air, so you will be more likely to encounter a meteor-worthy sky soon after the high pressure has become established. For a quick transparency check, look towards the horizon just after sunset. Orange or pink haze near the horizon usually means a hazy night to come.

Satellite images showing cloud-cover across Europe and the British Isles, updated at regular intervals, are available via the Internet, along with forecast notes for specific locations. Don't place too much reliability in these however, since they frequently fail to indicate the kind of small-scale variations which can give one place a clear enough sky for meteor watching, and another a few miles down the road an entirely overcast night. The best method to ensure you see as much as you'd like of the meteor activity is to keep checking the sky regularly all night when a significant event is due. Set the alarm, have a nap, and check again in another couple of hours if conditions seem especially unpromising.

By Shelagh Godwin & Alastair McBeath