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Southern Leonid Watch 2001


updated 27/11/01 The Leonids were fantastic!!! I've only just got back from Alice Springs and still haven't developed my films. People are still collating data. I have put an account of my observations, some preliminary graphs and some links on this page.


The Leonids are a meteor shower that originates in the constellation of Leo, (the lion) and occur regularly. Their peak numbers are generally observed on November 16-17. This year in Australia, the peak should be on the morning of November 19. Aside from their occasional spectacular displays, the Leonids are important for understanding the origin of meteors and their relationship to comets, and play an important role in trying to predict meteor showers themselves. This year, a spectacular storm is predicted for Australia.

Meteors are the light trails we see when small dust grains or rocks enter the Earths atmosphere. Most of the meteors are caused by dust particles no bigger than a grain of sand. Meteor showers occur when a lot of dust and rock enter Earths atmosphere close together. These associations of dust and rock are thought to be debris ejected from comets (more rarely from asteroids), and the Leonids are associated with comet 55P/Temple Tuttle.

The meteors appear to radiate out from a single spot in Leo (the radiant). However, the meteors in fact are moving along parallel paths. They appear to radiate from this spot in Leo for the same reason that parallel railway lines, or any other parallel lines on the ground, appear to originate from a point on the horizon.

Comet 55P/Temple Tuttle orbits the sun with an orbital period of 33.2 years. In line with the comets return, every 33 years or so the Leonids give an outstanding display. The last big Leonid shower was in 1966, where the number of meteors ranged from 40 per hour to an estimated peak of 200 per second!

35 years, and a lot more modeling later, in light of the good display in 1999, the less spectacular display in 1998, and the ordinary display in 2000, it seems that 2001 will be a bumper year. More details can be found in the links section.

The 1998 Leonids were a subject of intense interest because of the predictions of that the 1998 shower would be a spectacular "storm". Popular media tended to ignore the warnings that the predictions could be wrong by orders of magnitude so when hundreds of people bundled up in the wee hours of the morning, some having driven a fair distance to get clear dark skies, a fair few were disappointed when instead of hundreds or thousands of meteors they got a handful. To be fair, those few were truly spectacular, and were the biggest and brightest I'd ever seen, and had meteor watchers everywhere excited. There just wasn't a lot of them.

In fact, while peak rates of 1,000-10,000 meteors per hour were predicted, the actual peak was around 250 per hour, and the peak arrived nearly 24 hours early! Predicting meteor shower densities and times is tricky at best, but the Leonids seem to be trickier than most. Analysis of the data suggests that if Earth crosses the orbit of Tempel-Tuttle too soon after the comets passage, then there is no storm, just a strong shower. Records show that no Leonid storm has ever occurred less than 300 days after Tempel-Tuttle passed by Earth's orbit and in 1998, Earth followed the comet to the orbit-crossing point by only 257 days.

The 1998 Leonid shower provoked a flurry of analysis, and new models, especially by Rob McNaught (ANU) and David Asher (Armagh Observatory), may have better predictive power. The times and densitites featured here are taken from their work. These predictions were spectacularly confirmed when the 1999 Leonids peaked with a ZHR above 5000 on November 18, 2h04m +/-5m UT (that's 1.04 pm daylight saving time in Australia) over the Middle East. Thus it seems that the peak time of 2h08m UT predicted by Asher and McNaught is confirmed within the margin of error, although the observed activity is significantly higher (>5000 vs 2000 predicted. Those Leonids apear to be from dust shed from comet Temple-Tuttle three revolutions, or nearly 100 years, earlier). For 2000, the Asher/McNaught model and the Lyytinen/Flandern model predicted 3 peaks with modest rates which corresponded pretty closely to the observed peaks seen in 2000. So their predictions for 2001 seem pretty likely.

Well, what about 2001. The majority of researchers predict a storm.

Both D. Asher & R. McNaught as well as E. Lyytinen, predict two strong peaks of the meteor rate on Nov. 18, 2001, one around 10 UTC with about 1000 meteors/hour and a double peak around 17 and 18 UTC with 6000 to 8000 meteors per hour.

A very different result has been obtained by B. Cooke of NASA's MSFC who, taking into account worldwide observations of the Leonids in 1999 and 2001, comes to the conclusion that there will be only one very broad and shallow maximum, peaking at a mere 1300 meteors/hour around 13 UTC.

A completely different model again was presented by P. Jenniskens at the Meteoroids 2001 conference in Kiruna. He saw two peaks, at the times predicted by Asher, McNaught & Lyytinen, but with the intensities the other way around. He has revised his data, with 4,000 meteors/hr at the 'American' 10 UTC peak and only some 2000/hr at the 'Asian' 17 UTC and 17:55 UTC peaks. The table below summarises the different predictions

Leonid storm predictions for November 18 (Universal Time), 2001 (figure in brackets are estimated meteors per hour)
												Group
Storm seen from             Asher/McNaught              Lyytinen           Jenniskens    Brown/Cooke
United States               09:55 UT (ZHR = 800 /hr)    10:32 UT (2000) 10:09 UT (4200)  none
California, Hawaii          none                        none            none             13:00 UT (1300)
West Pacific, Australia     17:24 UT (2000)             18:00 UT (2300) 17:08 UT (1800)  17:00 UT (500) 
West Pacific, Australia     18:13 UT (8000)             18:06 UT (5100) 17:55 UT (2700)  none
Whatever happens, Australian observers seem virtually assured of seeing LOTS of meteors.


When should I look?

There are three predicted peaks this year, as the earth moves through a number of dust trails that have been shed at previous passes of comet 55P/Temple Tuttle.The peaks with the greatest activity this year have been predicted to be at 10 hours universal time (UT), November 18, and 18 hours UT Nov 18 (actually, the second peak is a "double", with peaks at 17:24 and 18:13 UT). These dust trails were ejected from Comet temple-Tuttle 9 orbital revolutions (300 years ago) and 4 revolutions (134 years) ago respectively.

As the eastern seaboard is 10 hours ahead of UT, the 18 hour UTC peak occurs at roughly 4.00 am AEST on the morning of the 19th (not daylight savings, see Min ahead of UT for state by state times), when the radiant is well above the horizon, with a predicted rate of either 2,000 meteors per hour or 6,000-8,000 meteors per hour. Either way it should be a fantastic show. However, there should be activity well before then (see above, Min ahead of UT and below), and you also should start looking earlier to get your eyes dark adapted and to familiarise yourself with the sky.
The radiant in Leo rises after 2.00 am (1.00 am in Northern Australia). However, it's best to wait a bit longer, as until the radiant is about 20 above the horizon, atmospheric effects reduce the number of meteors you can see. For most cities, this does not occur until about 3.30 am local time, but you should start earlier (say 3.00 am) because of the early peak predicted by Lyytinen and the relatively narrow viewing window. The number of meteors you can see after the start of twilight rapidly diminishes, so there will be a narrow window for observation in most states, lasting from approximately 3.00 am to 4.00 am (See the table below). On the other hand, it would be best to be up a little earlier just in case the shower comes early, so 2:30 am may be an ideal time to start watching. This is a comprise between radiant height, beginning of twilight, and the possibility of a peak on or earlier than 3.00 am. Observers in South Australia and the Northern Territory should naturally start observing half an hour earlier, and in Western Australia two hours earlier.

The best sites for observation are in the Northern Territory and Western Australia (although Perth tends to miss out a bit because of the low radiant height) where there is roughly a three hour window of dark skies. The worst site is Tasmania, where it is unlikely that anyone will see anything.

City		Radiant		1st Peak	Twilight	Sunrise		Min ahead of UT
==============================================================================================
Darwin		30		2:54 am		4.56 am		6.00 am		570
Brisbane 	30 		3:24 am		3.23 am		4.48 am		600
Sydney 		23		3:24 am		3.09 am		4.43 am		600
Melbourne    	20		3:24 am		3.18 am		4.59 am		600
Hobart 	         16		3:24 am		2.43 am		4.06 am		570
Canberra	20		3:24 am		3.12 am		4.47 am		600
Adelaide       	20		2:54 am		4.14 am		5.41 am		570	
Alice Springs	25		2:54 am		4.27 am		5.54 am		570
Perth		22		1:24 am		3.34 am		5.08 am		480
===============================================================================================

Radiant: This is the height of the radiant above the horizon in degrees at 3.30 am local time, NOT corrected for daylight saving. Twenty degrees is about 4 handspans.

1st Peak: This is the time of the first of the two peaks predicted by Asher and McNaught, NOT corrected for daylight saving. Lyytinen predicts this peak will turn up half an hour later, Jenniskens predicts it will turn up half an hour earlier. See Min Ahead of UT for the times of the second peaks.

Twilight: Time that local twilight starts NOT corrected for daylight saving. This will be the approximate time when meteors viewing will start to deteriorate.

Sunrise: Time of local sunrise NOT corrected for daylight saving.

Min ahead of UT: Minutes that local time, uncorrected for daylight saving, is ahead of Universal Time. The Leonid peaks visible to us are using the Asher McNaught predictions to be at 17:24 and 18:13 hr UT November 18, this translates to :
3.24 and 4.13 am local time Monday, November 19 for most of the eastern seaboard,
2:54 and 3:43 am local time Monday, November 19 for Darwin, Adelaide and Alice Springs
1.24 and 3.13 am local time Monday, November 19 for Perth.

It best to start observing some time before the peak to allow your eyes to adjust, also in case the peak comes earlier (The Lyytern Flanders predictions are for 17 and 17.55 UT, roughly 30 minutes earlier). Also, it's nice to watch the build-up to the peak as well.

Why haven't I corrected for daylight saving? I am too lazy too took up when each state does/doesn't go onto daylight saving and apply the necessary corrections.


Where should I look?

leo in the morning

The view facing east on the morning of Monday, November 19, 3.30 am AEST (4.30 am daylight saving) . Leo is low in the north-eastern horizon.

A black and white star map of the northern November sky at 3.30 am (4:30 am daylight saving) on Monday 19 November can be viewed here (nov_leo.gif 18 Kb). Clusters and Nebula brighter than magnitude 5.5 are marked as circles and squares respectively. The approximate location of the Leonid radiant is marked with a large circle.

A high resolution PDF file can be obtained for the the leonid radiant map (95 Kb). You will need a PDF viewer such as Adobe Acrobat or GhostView to view and print them. They look slightly worse on-screen than the GIF files, especially as Acrobat 3.0-4.0 can only display them side on, but print much better and come with legends. However, Acrobat 4.05 can display them in the proper orientation.

The above maps and all descriptions below are based on the view from Melbourne at 3.30 am local (non-daylight saving) time and assumes a fairly level horizon.

Face north. About five hand spans above the horizon you should see bright Jupiter. Seven hand spans to the right brings you to the bright white star Alpha Leonis, Regulus. Following down and to the left from Regulus you will see a number of fainter stars which form a sickle shape, the head of the lion. The radiant of the Leonid shower will be roughly in the center of the curve of the sickle, about one finger width up.


What should I see?

Asher-McNaughts predictions are for a peak of 6000-8,000 meteors per hour (another prediction is for around 2,000 meterors see Above) visible from Australia. These predictions are somewhat soft, as we have little historical data on encounters with these dust trails. Unlike other years, Australia is ideally placed, and weather permitting, we should be in for a fantastic show. At the above rates you should be seeing about every one to two seconds.

The meteors themselves should be quite bright, possibly as bright as Regulus or Sirius.

Note that these are predictions, and meteor showers are notably hard to predict, as we found out in 1998 and 1999. We think these predictions are much better than earlier ones, but there may still be other factors that have not been considered. The actual rates may be ten times higher or lower than noted here. Also, the peak may turn up earlier or later than predicted. In fact, the meteor streams might miss the Earth entirely. However, even a rate of 50 meteors per hour is worthwhile watching, and there is always the chance you will see many more. Furthermore, I must stress that observations of these meteors in Australia are important for testing and refining models of meteor storms, and making more accurate predictions.

NASA have a web based program that will predict the Leonid intensity at your location.
It is at http://leonid.arc.nasa.gov/estimator.html

It is "hard wired" for Adelaide, Brisbane, Alice Springs and Perth. For other sites, you will need to know your latitude and longitude (usually in the back of an atlas). For major cities the values are:

City       Latitude      Longitude     Hours Ahead of UT (NOT daylight saving)
========================================================
Canberra   35.28 S	 149.12 E     10
Darwin     12.37 S       130.90 E      9.5
Hobart     42.90 S       147.30 E      9.5
Melbourne  37.45 S       144.97 E     10
Sydney     33.53 S       151.17 E     10  
==========================================================

Observing conditions on the night might not be ideal. Cloud cover and sky haze can get in the way. People in the city will see far fewer meteors than those in the country, so you might consider going out to a park on the edge of town if you are a city dweller. Given the possible magnitude of the event, you might even consider going a few hours out into the country, as this not only gives darker skies, but also increases the viewing time.

To check the weather forecast, go to the Meterology Departments forecast site, or alternately the Weather Channel.

At the very worst, under clear skies, you will see a nice sunrise, with Jupiter and Saturn in the north, and a host of interesting constellations, the sky will be quite beautiful. And there is the chance you will see something quite amazing. Isn't that worth getting up early for?


What do I need?

For meteor watching, very little is needed. Basically, all you need is you. If you want to try and count the meteors, you will need a couple of sheets of paper, a pencil and a good watch. Bundle up against the predawn cold (I really mean this, I had a jumper and a windproof and I was seriously cold), bring a reclining chair if you have one or a good picnic blanket, and find a dark site with a wide-open view of the sky. Then just lie back, relax, and look up at the stars.

Optional extras are a torch with red cellophane over the buisness end, and a thermos of something warm to drink. Mosquito repellant is also a very good idea.

Also, use common sense in choosing a viewing site. Lone persons should not choose dark parks in the seedy part of town to watch the Leonids, as a mugging can ruin your entire day.


Observing the leonids

Several amateur astronomy groups have meteor watch sections. If you wish to participate, why not contact them, a list of Australian astronomy goups and their meteor sections is given below.

If you wish to try your hand at visually recording the Leonids, here's what to do.

What you will need

Note that these methods are very rough and ready compared to the techniques used by "professional" amateur astronomers, (for example, I have ignored quadrants and a few other niceities) but they will give a decent impression of the Leonid shower.

To observe the Leonids this year, look slightly above the radiant, by roughly a handspan, so that you have the widest possible field of view unobstructed by the horizon. How will you know the meteors you see are Leonids? Normally you take a line of sight to see if it originated at the radiant. This year, it should be rather obvious. However, following the International Meteor Organisation's lead, I have calculated a few lines at the sky along which Leonid meteors may travel:

   Alpha Gemmini -> beta Tauri -> Jupiter -> Gamma Ceti
Alpha Canis major -> Kappa Orionis -> 27 Erandi
psi Velum -> beta Carinae
Alpha Hydri -> Zeta Puppis -> Alpha Carina
Delta Crateris -> gamma Centauri

If you choose your field of view in the general area of the constellations mentioned above (check the acompanying maps), you can classify a meteor as a Leonid if it travels parallel to the lines above (in the right direction, of course, and the right - very fast - speed). At the peak, the meteors will be just too fast to do this, but its unlikely that there will be significant numbers of sporadic meteors interfering.

Left field Guide Star Map
Right Field Guide Star Map
The Key guide stars are indicated on the map. I haven't joined them with lines as the map projection distorts them.

Starting the observations

Allow at least 10 minutes for your eyes to get accustomed to the dark, then write down you starting time. Also make a note of how cloudy the sky is. If cloud covers more than 20% of the sky, you will miss many meteors. Look in the general direction of Leo, around 1 hand span up from the radiant, and start counting.

Counting Meteors

Quite simple for small numbers of meteors. Just count the meteors you see by making a mark on your paper, and write down a direction (up, down, left, right) an approximate magnitude (see below). To make recording simple, use a simple code such as 4u for a 4th magnitude meteor travelling up from the horizon. Every 10 meteors, note down the time and repeat for the next 10 meteors.

When high rates occur, just write down a tick for each meteor and give an avearage magnitude every 10 meteors or so. 2000 meteors per hour is about one every two seconds, so you will have to be on your toes. Still write down the time every 10 meteors, you will miss a few doing so, but it won't matter that much at very high rates. If the rate is really high just choose a small section of sky and count in that, then do an estimate based on the patch you are watching.

If you have a tape recorder (remember them) and a blank tape, you can just speak a magnitude into the tape recorder, and a time after every 10 meteors. Then later playback and count the meteors that way.

Estimating magnitude

This is a little tricky, but can be done with out too much pain. Looking at Leo, Regulus is roughly magnitude 1, the star immediatly below it is about magnitude 4, the star immediately below that is about magnitude 3, the star immediatly to the right and down two finger widths is magnitude 5. To the left of Leo by about 4 handspans is Castor and Pollox, approximate magnitudes 2 and 1 respectively. Directly above is bright white Sirius, at roughly -1.

From this you should be able to get a rough idea of the magnitude of a meteor, if it is brighter than Castor, but not brighter than Regulus, record a magnitude of 1. If it is brighter than the star immediately below Regulus, but not brighter than the one below that, record a magnitude of 3.

Again, this is much more rough than the techniques dedicated meteor watchers use, but it will give you some reasonable idea of the brightness. Don't stress too much about it, but if you want to get a feel for this, why not try checking out the relative brightness of the stars on a dark night before hand.

Finishing Observations

For most places, by 4.00 am the sky will be too light to see all but the brightest meteors, so stop then. For Northern Australia, 5.00-5.30 am would be a good time to stop. Afterwards, go get a cuppa, and write down your observations of a better sheet of paper, adding any useful comments (like cloud cover).

Lunar Leonids

In 1999 impacts of Leonid meteors were recorded on the Moon. This was the first time meteor impacts had been recorded on another world. This year, during November 18, a storm of Leonid meteors is expected to hit the dark side of the thin crescent Moon. The revised time of the Lunar Leonid maxima is when the moon is well below the Australian horizon on the Eastern seaboard. In Western Australia, the Crescent Moon is 4 hand spans above the horizon when the first stream hits at 8.00 pm local time. For Adelaide Darwin and Alice Springs the Moon is a hand span above the horizon at 9.30 pm local (not daylight savings) time when the stream hits. It might be worth while looking anyway, just in case the meteor stream comes early. More information about lunar meteors and how to observe them can be found at http://iota.jhuapl.edu.

Detailed information is given at the ALPO Lunar Section lunar impacts web site at
http://www.lpl.arizona.edu/~rhill/alpo/lunarstuff/lunimpacts.html
At that site, read the top and click on the large type "Lunar Impact Alert Notice!" that has the direct link http://www.lpl.arizona.edu/~rhill/alpo/lunarstuff/impactalert.html

Radio Leonids

You can pick up meteors using just your car radio. Strange but true. This is a good method for picking up meteors after the sun has risen. The Radio Leonids page will tell you all you need to know about using your radio to pick up the Leonids (or any other meteors).

For this years Leonids an observer in Japan has put together a project involving 67 sites in 12 countries. Now most are actually schools in Japan but there are also a few others around the world that will be (are) contributing data.

http://homepage2.nifty.com/~baron/radio.htm
http://homepage2.nifty.com/~baron/leo01p.htm
http://homepage2.nifty.com/~baron/leo01pmap.htm

Three observers have a separate site that will show their data as graphs and text. I've been updating mine as often as possible and from November 14 onwards it will be hourly if possible.

http://radio.data.free.fr/

Some of this data will be uploaded to a NASA web site. You can also hear the real time sound output from several systems.

http://www.spaceweather.com/
http://www.spaceweather.com/glossary/nasameteorradar.html

Many thanks to Bruce Young for this update

Amateur radioastronomers can also pick up meteors with their rigs. This site for radioastronomy amateurs shows you how to build a simple rig, and how to detect meteors with it.


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Created: Friday, 31 August 2001, 11:22:13 PM
Last Updated: Friday, 31 August 2001, 11:30:13 PM