Leonids 2000 observational campaigns
The Leonid meteors will soon be back - and although this year's shower is not expected to reach storm proportions, ESA scientists are continuing their efforts to learn more about the cosmic debris that is incinerated as it enters Earth's upper atmosphere.
This year, there are three different observational campaigns involving scientists from the European Space Research and Technology Centre (ESTEC) in The Netherlands.
Looking at the Leonids
Detlef Koschny is hoping to obtain three sets of simultaneous video observations on the nights of 16-17 and 17-18 November. While Koschny's cameras will be located in the Harz Mountains of Germany, his colleague Joe Zender will be duplicating the observations in the north of the Netherlands. A group of Dutch amateur meteor observers will also be assisting by making their own observations from a third site.
By using automated video cameras to continuously watch the same region of sky from three different viewpoints, the scientists hope to be able to calculate the altitudes and orbits of the dust grains entering the upper atmosphere.
In addition, meteor detection software will be able to scan the stored video images, eventually enabling the scientists to determine the numbers of meteors down to magnitude 8 or 9 (about 10 times fainter than the human eye can see).
"The video cameras have very sensitive, wide angle lenses. They will be generally pointing away from the Moon, since its glare tends to hide the fainter meteors," explained Dr. Koschny. "By using different sites, we will obtain stereo observations of the same meteors.
"We are not expecting to see as many meteors as last year, when there were several meteors a second at the peak period, but we may see a few hundred meteors an hour," he added.
See also: Leonids 2000 Reports.
Listening to the Leonids
Jean-Pierre Lebreton and Trevor Sanderson from ESA's Space Science Department at ESTEC will be using radio signals rather than telescopes or cameras to observe the elusive meteors. Their technique uses the ability of plasma (ionised gas) clouds around glowing meteor trails to reflect radio waves.
"Signals from HF transmitters above about 10-15 MHz are not reflected back to Earth until they have travelled a few hundred kilometres or more. This creates a `Skip Zone' close to the transmitter where listeners cannot receive the signal, whereas listeners further away can. It's when we listen in the skip zone that we can best receive HF signals reflected on meteor trails," explained Dr. Sanderson.
"The night time is much less effective in reflecting HF signals in the range above 10-15 MHz. The signals at those frequencies escape into space, so the HF radio stations are usually shut down after dark. However, meteor trails can also reflect HF radio signals for brief periods at night," explained Dr. Lebreton.
This means that, at night, instead of no radio reception at all, the team can pick up brief transmissions every time they bounce off a meteor trail.
"For our experiment during night time, we have come to an arrangement with Merlin Communication, the service provider for the BBC, to continue their transmissions at 17.64 MHz," said Lebreton. "They will switch on one of their transmitters every night between 13 and 20 November. We will then use the short-lived meteor ionisation trails as mirrors to reflect the radio signals. In this way, we hope to be able to count the meteor echoes."
Not only will this technique enable the scientists to make an accurate count of meteors, but it will provide information on the winds in the upper atmosphere.
"Because upper atmospheric winds move the `mirror' a little bit, it induces a very small Doppler shift in the signal we receive," explained Lebreton. "These minute changes in the signal frequency allow us to separate the reflection from the meteor and the main signal. The fixed frequency of the HF carrier wave and the small changes caused by the reflection will be automatically recorded as dynamic spectrograms.
"We will be using advanced signal processing software provided by Dr. Bev. Ewen-Smith from the COAA observatory in southern Portugal to record and display the data on our computer screens. He is offering the licences for this software at reduced price until 15 November to anyone who is interested in using this technique."
A similar experiment will be conducted by the Radio Society of Great Britain.
Preliminary trials conducted over three nights in early November picked up echoes from numerous sporadic meteors and demonstrated that the Doppler technique does work.
"Anyone tuning in their radio to the BBC frequency can try this experiment for themselves," said Lebreton. "It should be possible to pick up the echoes - each lasting a few seconds - from the UK and all over Europe. It will be an interesting challenge for the readers of our Web site!
"This is the best way to learn about meteor showers - it works day and night, and in all weathers. It should be possible to listen to the radio broadcast and hear echoes that will last for more than a few seconds. During the peak activity at around 4:00 GMT (5:00 CET) on 18 November, we may even be able to listen continuously to the radio programme!"
See also: Leonids 2000 Reports.
Tell-tale flashes on the Moon
Håkan Svedhem and a colleague from ESTEC's Space Science Department will be using a 25 cm telescope to observe the dark hemisphere of the Moon on the nights of 16-17 and 17-18 November, during next week's Leonid shower.
Attached to the telescope will be a video camera and a recorder, which Svedhem hopes will capture images of the tell-tale flashes that indicate Leonid meteors are striking the lunar surface.
"These flashes are very brief - they will only last one or two frames of the video," he explained. "We will be using special software to compare each frame with the previous one."
A similar Leonids observational programme from Tenerife in November 1999 was washed out by bad weather, but Svedhem is hoping for better luck this time.
"The meteor count is not expected to be as high this year and the phase of the Moon is not very favourable, so we are not too optimistic about seeing any flashes. However, next year the lunar phase is much better and the meteor predictions are higher, so this will be a useful trial for the 2001 Leonids shower."
See also: Leonids 2000 Reports.