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Astronomers' predictions indicate that the Leonid meteor shower could produce many more falling stars this year when compared to previous years. It is estimated that many thousands of meteors/hour could appear in a relatively ‘short’ period if you should be on the most favourite location. This years Leonid display could be a really thrilling event for locations in the United States, the eastern part of Asia and the western side of the Pacific Ocean, and Australia. Astronomers are therefore planning large observation campaigns all around the world.

Until now observing campaigns have consisted mostly of land-based observations.  Occasionally marine reports have been received but, historically, a large observing campaign covering the world's oceans has not yet been carried out. If ships at sea could contribute observations the whole observing-network could be upgraded and the Leonid dataset greatly improved.   The combined ‘meteor-counts’, from both land and marine-based locations could lead to a detailed analysis of the dust-distribution in the Leonid meteor shower thereby contributing to a better understanding of the formation of the comet-tail of the parent Leonid-comet.

Would you like to join the marine Leonid Observing campaign 2001?

Ship Masters and Officers are invited to participate in an observing campaign on a voluntary basis by responding to the e-mail address given at the end of this information leaflet.  If your vessel is not expected to be at sea during this period it is still possible to join the campaign.  When all observations have been gathered in the weeks/months after November 20th, the outcome of the data will be published in various magazines and papers and will also be published on the Internet.

The basics of meteor-observations

Meteor astronomy is generally done by astronomy-amateurs. There are only a few professional astronomers active in meteor research today; therefore the field relies heavily on the amateur for data. This data collected by amateurs can provide astronomers with valuable information on the origin and evolution of the Solar system. With minimal equipment, and knowledge of a few basic concepts, you can begin a successful pursuit of meteor observing.

Meteors, often described as ‘falling stars’, are typically small particles, normally no larger than a grain of sand, that enter our atmosphere at speeds of up to around 70 kilometres per second. They become visible at an altitude of about 100 kilometres due to their impact with the atmosphere. Most particles will evaporate from the effects of heat well before reaching the surface of the Earth. Those that do reach the surface of our planet are known as meteorites.

Although meteors can be seen on any clear night, your chances of seeing greater numbers will increase if a few key points are kept in mind. As moonlight and light-polluted skies wreak havoc upon meteors, it is preferable to observe when the moon is absent from the sky and from the darkest skies possible. Another important consideration is the time of night when the meteor watch is held. Due to the Earth's rotation it is preferable to observe in the early morning hours. At this time you are facing the direction the Earth is travelling in its orbit. Meteors will then collide with our atmosphere. At other times, meteors must travel at a speed that allows them to overtake the Earth. (This situation is similar to a car travelling through a snowfall where more snowflakes will strike the front windshield rather than the back.)

There are two broad groups of meteors; those that arrive from random locations in the sky which are termed 'sporadic', and others that appear to radiate from a particular region of the sky and come from meteor showers.  Sporadic meteors, also known as the sporadic background, generally produce only about 5 to 10 meteors per hour, but actually make up the bulk of meteors entering our atmosphere.  However the highlight for meteor observers are those nights when meteor showers are active. Although each shower is somewhat different, they normally last for several nights with a peak of activity occurring on a specific date. Your chances of observing meteors are greatly increased on a night when a shower is active as rates can range to 50 or more per hour depending upon the shower. These meteors can be distinguished from the sporadic background by the fact they radiate from one particular region of the sky known as the radiant. The Leonids of November, for example, appear to come from a location near the constellation of Leo

Where can I see meteor showers (in particular the Leonids) ?

Because meteoroid streams are always much wider than the Earth you can see meteor showers scattered over your whole sky! You don’t therefore need to face any particular direction to see a meteor shower well! Nor will a meteor shower be visible only from one area of the earth. Unlike geographically narrow astronomical events like Solar eclipses or Lunar occultations, a meteor shower will often be visible over much of the Earth's surface!

However, not all of Earth will be able to see a given meteor shower. This is because the bulk of our globe shields some areas of Earth's surface from the impact of meteoroid particles - in effect, some areas of the world map are always in the Earth's "shadow" with respect to any meteoroid stream. This "shadow" is bounded by the area of Earth in which a certain point on the Celestial Sphere is not visible. This special point is unique to each meteor shower, and is characterised as being the point in the sky to which all visible tracks from the shower - no matter where they are seen in the sky, or from what point on Earth - all seem to trace back to. This point is the "radiant" of a shower.

Finally, because there is often a fine-grained structure within meteoroid streams, which the earth will "sample" as it passes through them from hour to hour, not all areas of the Earth will necessarily see the exact same show from a meteor shower! For instance, the peak activity for a particular shower may occur while it is daylight in your area of the earth.  Alternatively, it may be dark during the shower's peak "maximum", but the shower radiant point may be low on your horizon, thereby reducing the number of meteors you see - or it may even be below the horizon, making it impossible to see any meteors. Watch when you know a meteor shower radiant is above the horizon. No meteors can be seen from a shower when it's apparent "radiant" is not in the sky! The radiant of the Leonid meteor shower is up by around midnight, so you're generally safe watching after then.

The Latitude of your observation position is also important. The position of the radiant of the Leonids varies from place to place and also from moment to moment. The higher the radiant is above the horizon the more meteors could be seen at the maximum-moment. At very northern latitudes the radiant is quite long above the horizon but is also staying quite low above that horizon too. In the tropics the constellation of Leo will rise high in the sky near dawn and in the Southern Hemisphere we will be confronted with the long duration of the November daylight period. Mid-Northern latitudes therefore seem to be the most favourite position, although apparently less favourite Latitudes could also experience an impressive celestial show.

Watch from the darkest site you feel safe at: this means getting away from all man-made lights, and also trying to watch when the moon is not in the sky (or is a very thin crescent). In November 2001, at the moment of the Leonid-meteor shower, the moon will not be present in the night-sky. Man-made light   from shipboard sources should be avoided if possible in order to get a truly dark meteor-filled sky.

Watch from a spot without obstructions, ideally on a clear night: Obviously, if there is an area of the sky you cannot see, you will miss the meteors that appear in that part of the sky! For the same reason, try facing high enough up in the sky so that no part of the horizon blocks your view.

When can I expect the meteor shower ?

The Leonid 2001 dust stream will most likely be divided into at least two main filaments. According to several computer computations the earth will cross a first filament core on November 18th at 1000 to1100 UTC.  The core of a second filament is on our planet's path some 8 hours later, around 1800 to1900 UTC. According to these computations a good position for observing the first peak will be in the region of the East Coast of North America and the second peak in the Western Pacific. Over Australia the second peak could give also a good show with radiant heights between 30 and 40 degrees.

The passage through each filament will take some hours, so the observation campaign for each filament of the meteoroid cloud will consist of at least 2 to 3 hours. However meteor counts should ideally be obtained from as long a period as possible.

The best observation periods are probably those mentioned above which are derived from computations. In reality however there may be some undiscovered filament(s) at other times in the period between 17-20 November (maybe already appering from the 14th of November till the 22nd of the month). It is important therefore to be prepared for sudden increases in amounts of Leonid meteors throughout the 3 observation days. (If you have time please also report your observation counts over the ‘low-activity-time’ of the mainstream period).   If you have observed the nightsky and didn’t see any meteoractivity, also that information is valuable for the astronomers. So if you have made an observation, always tell us what you saw, many meteors, some or no meteors, all pieces of information are even important!

It is essential that the same time zone description - UTC (GMT) - is used  in your observation messages and reports.

How do I count the number of falling stars?

Scientists are eager to get counts of meteors over a specified time period, for instance 30-seconds, 1 minute- or 5-minute periods. The level of activity itself will determine which counting period should be used. If at a certain moment the number of meteors is rising quite dramatically, perhaps more than 20 meteors per minute, you should try to count the amount in small periods of 30 seconds each.   Otherwise a totality count over 1-minute-periods is sufficient.  If activity is low, you could make a total-count over each 5-minute-period.

What about the observing conditions ?

Another important factor is the condition of the sky at the time of observation e.g. the transparency and the amount of cloud covering the celestial bowl. Together with the meteor counts a description of these conditions is essential, especially when observations have to be compared to each other at a later date .

The transparency of the night sky at dawn can be measured by estimating which stars can be seen. If hundreds/thousands of stars are visible the sky can be said to have good transparency. In a hazy sky only the brighter stars remain visible (some dozens over the whole sky), and in very hazy or misty situations only the very brightest stars will stay in sight. Ideally the magnitude of the stars that can be seen should be noted; magnitude +6 is the normal faintest star category and magnitude – 4 the brightness of planet Venus at its most brilliant appearance. The brightest stars normally reach magnitude 0 or –1.

To estimate the amount of cloud over the whole sky, please use estimated cloud amounts as for your meteorological reports - in octas of the whole sky. Two octas (2/8) will give a good view of most of the sky, six octas (6/8) some gaps in a rather obscured sky.

Remarks

It is important to report the exact amount of total observation time i.e. not just those counted during your own watch onboard. If someone is watching the sky each hour for 5 minutes, this should be noted with beginning and end-time.

Details of the format in which observation reports should be submitted are attached herewith.  Additional observed details e.g. fireball-appearances, general brightness of meteors, etc are also welcome and can be included in the “remarks” section of your report.

Contacting the campaign-co-ordinator

A special e-mail address kuiper@knmi.nl has been established for contacting the co-ordinator of the marine-Leonid 2001 observing campaign, Jacob Kuiper, Senior meteorologist at the Dutch National Meteorological Office. This address can be used to register your participation in the campaign and, from November 17^th, will be used to receive your Leonid observations.
It would be appreciated if copies of your Leonid observations could also be sent to obsmar@metoffice.com  in order that they may also be considered for inclusion in a future issue of The Marine Observer

Some interesting other meteor-internetsites could be found at:

http://www.dmsweb.org
http://www.arm.ac.uk./leonid/dustexpl.html
http://www.imo.net
http://www.xs4all.nl/~carlkop/astroeng.html

Content of Observation reports

Observation reports should follow the following format