SHOOTING STARS
The UK-China Leonid Meteor Shower
Observation Project

It is possible to undertake more advanced observation using photography, video and radio techniques. These all require equipment that is more expensive than the simple methods outlined above, but most of it is readily available in some form. These tasks are generally more suited to older students, though young ones may enjoy doing some basic astro-photography.

MAKING A PHOTOGRAPHIC RECORD

If you have access to a camera, you may be able to take photographs of the Leonid shower. The following suggestions are made to try and make your task easier.

This Nikon old SLR camera fitted with a standard 50mm lens is ideal for snapping the Leonids. The only extras are the clamp bracket and the cable release. The clamp is suitable for mounting the camera to a table or other firm fixture. But make sure that whatever you use, it is firm. Even the slightest jolt or vibration will ruin your pictures. It is much cheaper than a tripod which is the alternative, and can slip into you pocket. Note that this cable release has a screw lock so you can set the shutter open and walk away. You don't need to hold it the whole time the shutter is open.
 

How to proceed

1. Decide if your photograph is intended as a piece of photographic art, or as a record. In other words, are you really interested in just getting a pretty picture? If so, then you will need to tackle the task differently, carefully choosing your skyline etc. If you want a record, then you can be less selective in this respect, but you will have to pay more attention to recording what you see.

2. Choose a fast film, ASA 400 or faster, if the sky is dark. If however you live in an area heavily poluted with light use slow film - ASA100 or less.

3. You should use a camera which has a "B" setting, which allows you to hold the shutter open for as long as you like. Your camera should be mounted on a sturdy, stable tripod so that it doesn't shake. If you don't have a tripod, place it on a table or other flat surface, making sure that it can't wobble. You could also make your own camera mount. This time of year (November) it is advisable to use some sort of heater to keep dew from forming on your lenses and gratings. This is a real problem during long exposure photography, particularly in the UK!

4. Use a standard 50 mm lens, but you can get better results with a 35 mm lens, which allows a wider view, but reduces image size.

5. Use a cable release to avoid shaking the camera.

6. If possible, do some experiments photographing the night sky in the weeks before the shower, so that you get used to the best camera settings for you. If you can't do so, then set the lens to f5.6 or f8.

7. Observe the shower for a short while so that you can see where the radiant is. Don't point the camera directly at the radiant, but to one side or one corner - this will help you get a more definite "streak" from a meteor.

8. Record carefully the following information on your star chart or on a note pad.: Frame Number Film Type and Speed Aperture Time taken.

9. If the shower is intense, you can probably use a shorter exposure time. If it is fairly slow, then you can lengthen it accordingly. It may be possible to wait until you see an event before you take your photo. If the rate is slow, then shut down the stop, open the lens, wait for an event, then close the lens.

10. You may be able to get useful results from a simple camera, just by pointing it at the sky, and taking the photo, so long as the film is fast and you can control the shutter.

11. Warn your developer about what you have been photographing - he or she may think the film is ruined otherwise!

I have tested out my cameras on fireworks, to get some idea of the correct exposure. The night was cloudy and the fireworks display was in our city, which is heavy on light pollution and orange sky glow. Using 200 ASA film and a setting of 1/30 second at aperture f.2, I found the sky began to show up as a muddy ochre, which detracted from the firework plumes. However, when set at 1/60 and f.2, the sky was a nice inky black, and the fireworks showed up well, in something akin to the right colours.

Now, the problem is this, the fireworks are probably magnitude -6 and brighter, but most meteors are likely to be fainter. So what setting do you try? Depending on the sky glow, something around the settings I have suggested would seem to be a good idea. There are problems, however. Meteors even in a shower are infrequent and unpredictable. You will almost certainly need to leave the shutter open for minutes to get a reasonable photograph.

I can see a couple of solutions, which may go some way towards reducing the unwanted effects of skyglow. You can use a slow film, say 100 ASA or less, and you can adjust your camera apperture to the minimum stop, which will be f.16 or f.22 probably. This will enable you to increase the exposure time.

Using 100 ASA film, eight seconds at f.22 is equivalent to 1/60 second at f.2 using 200 ASA film, but this is a long way from the minutes-long exposures that you will find necessary.

METEOR SPECTROSCOPY

At first sight meteor spectroscopy might seem a little difficult and rather hit-and-miss. Ed Majden a veteren meteor observer in Canada, however, suggests that the Leonids offer an excellent opportunity to do some valuable work. And schools and amateurs can help in this.

Getting a spectrographic record of any astronomical objects tells us a lot about it, not least what it is made of. The colour of the light it emits and more important, the emission and absorption lines within that light - seen as a spectrum - can identify the substance from which the object is made, as sure as finger prints identify a suspect.

Most schools will have diffraction gratings in their labs. This can be used with a camera to create spectral images. Simply mount the grating in front of the camera lens as descibed below.

If you are doing serious scientific studies and have the experience and ability to analyse the spectral images yourself or want to send the results to an expert, you will want to use monochrome (back and white) film such as Kodak Tri-X Pan or Ilford HP-4 or HP-5. This is more or less consistent in sensitivity across the whole visual spectrum and will produce accurate results. Colour film, however, is made up of three layers that are sensitive to narrow bands of colour in the red, green and blue. Senitivity between these colours is lower, so a false indication of the spectral properties is likely.

However, if you only wish simply to demonstrate the principle, test your methodology and create some nice coloured images, then use colour film. The results can still be interesting and artistic.

This is what Ed says...

A meteor spectrum provides more information about a single meteor than any other method of observation. Generally, rather expensive precision replica transmission gratings are used as objective dispersive elements. It may be a bit late to suggest this for the Leonids but have you considered spectroscopy? I have experimented with an inexpensive thin film type 750 l/mm holographic grating available from Learning Technologies Inc in the US. When placed in front of a normal camera lens the spectra of very bright meteors will be recorded, around -3 magnitude and brighter. Analysis of the spectra is rather complex and will have to be done by professionals specializing in this study. Good spectra are of interest to them so they are interested in examining spectra obtained by amateurs. The best will probably be selected for measurement. During the last Leonid event in 1966 several Leonid spectra were secured by a Canadian meteor astronomer, Dr. Ian Halliday and a group in Japan. It would be important to get more spectra from this shower.

Ed adds...

For meteor photography, you take extended time exposures.

1. Mount your Camera on a sturdy stationary tripod.

2, Aim the camera about 20 to 40 degrees from the radiant, aligning the grating so the expected flight path of the meteors are parallel to the grating rulings, not across them.

3. Set your camera for time exposures. Normally this is the "b" or bulb setting on the camera. Use a locking cable release so time exposures are possible.

4. With a small format camera, such as a 35 mm, take several 5 to 10 minute duration exposures in succession. You are doing this with the hope that a meteor bright enough to be recorded will cross the camera field. Keep good records of start and end times, etc.

5. If there is a meteor storm, keep the time exposures toward the short end, 5 minutes or so. You don't want overlapping spectra, although it may be important to capture more than one spectra on each frame for what is called, time resolved studies.

6. If you have a number of cameras cover as much of the sky as you can.

7. If possible, mount a chopping or interupting rotating shutter infront of the camera for velocity and train studies. This shutter should be driven by a synchronous constant speed motor, interupting the light entering the camera from 10 to 60 times per second. For the Leonids any rate between 20 to 60 times per second is good.

Ed Majden

A practice photograph using fireworks as a test subject produded this image. The spectrum on the right was created by a 600 lines per mm diffraction grating. Note, however that there is a loss of colour between the three primaries - blue, green, red. This is a shortcoming of the film, which is not very sensitive in these wavebands.

MAKING A VIDEO RECORD

Video cameras can be used to great effect for the observation of meteors. However, you will need the camera coupled to an image intensifier if you are going to use this technique for serious study and analysis. If you are simply going to make a video record of the 1998 Leonids event you need nothing more than a standard camcorder with good low light performance. In this case think more along the lines of making a video for entertainment and for general historical value rather than using the camera as a scientific instrument.

If you do have the necessary equipment (Lenses, image intensifiers and recording systems) you may like to undertake a CCD based study. This though requires a good deal of painstaking analysis effort after the event, so be prepared, if you take this path. It is suggested you consult the IMO web site for detailed information on video techniques, at: http://www.imo.net/index.html

Results from investigations with video systems have been published by several amateur and semi-professional groups associated with the IMO. Here are some investigation examples:

images from meteors and fireballs slow motion sequences of meteors meteor shower images meteor shower sequences sonic booms from fireballs radiant plots activity graphs meteor cluster analysis meteor light curves meteor spectra comparision of video observation and other methods

How about Radio Techniques of Observation? Next.

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