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Leonids 2002

The Last Great Meteor Storm

November 18 / 19, 2002

On the night of November 18th / morning of the 19th we will experience the last great meteor storm of this decade. In fact the next Leonid storm won't occur until 2033, so if the weather cooperates this is it for photographing a meteor storm in the lifetimes of many of us.

Now, don't misunderstand. The Leonid meteor shower occurs every November, and there are other meteor showers each year, but we're using the word "storm", because rates as high as 2,000 — 4,000 an hour can be expected. That's about 1 per second.

Meteors are typically tiny particles the size of grains of sand that burn up as they enter the atmosphere. The Leonids are the tail of comet 55P/Temple-Tuttle. The storm is caused by the Earth entering one of two major dust trails of the comet, and the reason that we won't have another storm for more than 30 years is that the Earth's orbit won't cross these trails again till then.

The Moon and The Weather

That's the good news. The bad news is that there are two things that can get in your way. The first is, of course, weather, and the second is the Moon. Weather is always a factor in any type of astronomical observing, and at this time of year the odds are against us. And, unlike last year when we had dark skies for the Leonid meteor storm, this year there is an almost full moon that will be low on the western horizon (for those of us in northeastern North America), and it will wash out the fainter trails.

For those strictly interested in observing this phenomena this is a detriment, but for photographers this could work to our benefit. Only the brighter meteor trails will be recorded on film or digital in any event, and the moon near the horizon can be used as part of the composition if you're facing west. It will also illuminate some foreground objects if you face east.

This annual meteor shower or storm is called the Leonids because its radiant (where the meteors first appear) is in the constellation Leo, which is high and to the east. But, as we saw last year, the trails can stretch far across the sky and can be photographed in virtually any quadrant of the sky.

Milky Way, Muskoka — September, 2002
Canon EOS 1Ds with Canon 15mm f/2.8 Rectilinear Fisheye lens @ f/3.5. ISO 400. 73 second exposure.
This photograph doesn't show any meteors but does show how how effective a digital SLR can be in capturing faint stars. It also shows how important the use of a very wide angle lens can be in avoiding blurred stars. See below for more on this.

Timing is Everything

For eastern North America there will be two peaks. The first will be at 11pm on Monday the 18th. There are two problems. The moon will be fairly high at 61 degrees elevation, and the radiant (where the meteors appear to come from) will be very low in the eastern sky. But then at 5:30am the next morning (the 19th) the earth passes though the second tail and conditions are much better.

Sunrise will be at 7:15am, so at 5:30am there's almost an hour of darkness before first light. The moon is also much lower in the sky, at about 11 degrees above the horizon, setting at 6:45am. So, between 5:30am and 6:30am we'll have a moon that's very low in the sky (at 292 degrees Azm — just north of west) meteors will be at their peak and the sky will still be dark.

Meteor trails will be coming from the east and passing overhead. If you face west you'll be able to include the low full moon and have trails coming in from the top of frame. If you face west you'll have meteors coming towards you and moonlight illuminating the foreground. By 6:30am the show will be over and first light will wash out any meteor trails still visible. Time for breakfast and to drive back to the city and go to work.

Please note that all of the above information is for northeastern North America. Please check with one of the astronomy web sites, magazines or your local newspapers for details on your part of the world.

Last Year

Last year (2001) also saw a Leonid meteor storm. My shoot was a real fiasco, but I learned a lot and had a good time. I wrote about preparations and provided some tips, and also chronicled the screw-ups that happened which prevented me from getting any worthwhile images. This year, if weather permits, I hope to be a bit luckier (and more prepared). My write-up on last year's preparations and results can be found here, but I've repeated all of the technical advise so all you really need to read is this page.

Location

The prime radiant (the spot in the sky from which the majority of meteors will appear to originate) is fairly high in the eastern sky. Try and find a spot to shoot from that has a south eastern exposure. Trees in the foreground are not a problem as the radiant is quite high, about 40 degrees above the horizon.

Tips

Clear Skies: Check the weather forecast. If there's a decent forecast, head out to a dark sky location. Even though you may not have 100% clear skies, it still will be a worthwhile show. If the forecast is for overcast and/or rain, stay in bed. But, clearing can happen at the last minute, so what do you have to lose other than a few hours sleep?

Dark Skies: While you'll be able to see the meteor shower from the city, you'll only be able to effectively photograph it from a dark sky site in the country. If you have a friend with a country house, now's the time to call in a favour. Try to get at least 75-100 miles from the nearest major city. The reason for this is that you'll be taking long exposures. The sky glow from city lights will simply overexpose your film, just the way flare does during the day. 

Cameras: Any camera with a shutter than can take time exposures can be used. Set the camera to B or T. Use a locking cable release on B. If your camera has an electronic shutter see if it also has a long time exposure mode that doesn't draw current (like the Pentax 67II). Otherwise, put in fresh batteries and plan on replacing them the next day. Mechanical shutters are preferable for long time exposures for this reason. If you have a Canon EOS 35mm SLR or DSLR then this is a good excuse to pick up that TC-80N3 timer release you wanted but couldn't figure out when you'd use.

Digital Cameras: If you have is a digital camera, then give it a try. Otherwise, use a film-based camera instead. Astronomical CCD cameras designed for astrophotography have built in Peltier coolers. This brings their temperature down some 50 degrees F below ambient, thus reducing thermal noise. Therefore the lower the outside temperature, the better. The Canon D30 does a decent job on exposures down to about 20 seconds because of its special long exposure compensation mode. But, if you use this mode it doubles the time, since a 20 second exposure needs 20 seconds of post processing in the camera. The Canon D60 doesn't need this special long exposure mode but does a very good job nevertheless, up to several minutes before noise becomes really objectionable.

Lenses: You'll likely want to use the widest and fastest lens that you have. If you have something like a 14mm f/2.8 that would be ideal. The reason for this is twofold. Firstly, you want a wide lens because you want to show as much sky as possible as well as something recognizable as a foreground silhouette. This could be a lake, some trees or a house. Without a foreground subject what you'll have are just white streaks on film.

A fish-eye lens would be a good idea if you have one. I'll be using the Canon 15mm rectalinear fisheye with its 180 diagonal field of view. Prime lenses are better for this type of photography than are zooms, but if a zoom is what you have use it. Don't bother with anything longer than about 50mm. The exposure times will need to be too short, to avoid blurred star trails, as discussed below.

Film Speed: Film speed, aperture and shutter speed are of course all interrelated. We'll look at the each separately, but make your plans in the context of understanding how they combine to affect what you can achieve.

You can use any film speed from ISO 100 to 400. 800 or higher is simply too grainy / noisy and isn't needed. If you will be using an f/2.0 or faster lens then 100 speed film will be OK. If your lens is slower then ISO 400 is preferable. You can use color transparency, colour negative or B&W, though negative films or digital are preferred because of their greater exposure latitude. If you shoot B&W something like Ilford XP2 Super will give you good speed (ISO 400), reasonably fine grain, and convenient processing.

Aperture: The faster the better. But, don't just use your lens wide-open. Try stopping down at least 1 stop for some frames. So, if you're using an f/2 lens, stop down to f/2.8. The reason for this is that lenses are least sharp wide open and also suffer from coma at wide apertures. Coma is the inability of a lens to render a point source as a point, particularly at the corners of the frame. Instead they will appear to be smeared. Since there will be stars in your shot, which are of course point sources of light, any coma will be less visible if you're stopped down a bit.

Shutter Speed: This is the most complex of factors to be considered. You want a long enough exposure so that you capture a good number of meteor streaks, yet not so long that the stars themselves start to streak. Because of the Earth's rotation during the course of even a minute or less, any time exposure that includes stars will show them as streaks instead of points of light.

The simple formula for 35mm format is 600 / (Focal Length) = Maximum Exposure Time. So, for example, if you're shooting with a 24mm lens the math would be:  600/24mm = 25 seconds. (For medium format it's roughly half this number).

Aurora, Muskoka Ontario, Canada, October 28, 2000

Photographed with Canon D30 at ISO 400. 15 seconds @ f/2.5 with a Canon 50mm f/1.4 lens. RAW Mode. Long Exposure noise reduction mode ON.

This means that with a 24mm lens any exposure of longer than 25 seconds will show the stars as streaks rather than points of light. The frame above shows what I mean. This aurora photograph was taken with a 15 second exposure using a 50mm lens. According to the formula (600/50=12) a 12 second exposure was the maximum that wouldn't show star streaking. And sure enough, even the few seconds more used for this exposure starts to show slight streaking. 

You'll also see above that a 15 second exposure at f/2.5 and ISO 400 was more than enough to record the brighter stars. Meteor trails are often brighter than this (though many are fainter).

But, now you see the quandary. Even with a 25 second exposure using a 24mm lens, how many meteor trails do you think you can capture? Not many, unless we really have a "storm". So, the solution to either take take longer exposures and live with the star streaks, or many shorter ones hoping to catch some meteors in one or two of them?

Moonlight at Saddle Canyon, May 2000

This photograph was taken in the Grand Canyon at 2am under a full moon, and was a 4 minute exposure at f/4 with a 24mm lens on ISO 100 film. The star trails are just starting to appear long enough so that they don't simply look like bad blurs.

Update: Because of the full moon long exposures will be inappropriate this year. Too much light. Try and keep your exposures under the minimum needed to eliminate star trails and simply keep firing frames. If you are using a digital camera check the LCD for results.

For all the anal compulsives out there, here's the scientific formula for calculating star trail exposure times as quoted from Sky & Telescope...

The length l of a star's trail on the film in millimeters can be calculated from the formula

l = [tF cos (delta)]/13,750

where t is the exposure time in seconds, F the focal length of the lens in millimeters, and delta is the north or south declination of the star.

Happy?

 

Tripod: It goes without saying that you should use as large and as heavy a tripod as you have available. And a cable release. An intervalometer release like the TC-80N3 is ideal. I plan on putting mine on one camera and just letting it fire away unattended while I vary exposure, and framing with a second camera.

Clothes, Comfort & Accessories: Since it's mid-November, dress warmly. Bring a thermos of something hot. The trick for keeping warm is to wear a warm hat and scarf. The greatest heat loss is through the head, and the body's temperature sensor is at the back of the neck. That's why your mother told you to wear a scarf. Keep your head and neck warm and the rest of your body will feel fine. Gloves are a good idea too.

Flashlights are a must, of course. A small headlamp is very handy for nighttime and pre-dawn shooting as it keeps your hands free. Put a red filter on it to avoid ruining your night vision, or at least cover it so that it is as dim as possible.

Aiming

Aim your lens at about 45 degrees away from the prime radiant. This way you'll capture as much of the meteor trail as possible. With a 14mm — 21mm lens this will allow you to capture the prime radiant where they first appear and the full length of the meteor trails.

Focusing?

At infinity, of course. Remember to check that your lenses are racked over to their infinity stop before starting a series of exposures. If you are using autofocus lenses that focus past infinity be sure to autofocus them first on the moon and then turn autofocus off! Be careful — it's easy to make mistakes in the dark.

Good luck, and if you get any really great shots send them to me and I'll publish them here. Of, if you screw up the way I did last year, write to me with your anecdote.

Links

NASAAstronomy MagazineSky & Telescope Magazine


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Concepts: Film speed, Photography, Meteor shower, Leonids, Wide-angle lens, Exposure, Shutter speed, Digital single-lens reflex camera

Entities: Peltier, Ontario, Canon, North America, October 28, Saddle Canyon, ISO, Grand Canyon, coma, Michael Reichmann, Sky & Telescope, Aurora, SLR

Tags: meteor, trails, show, star, camera, meteor trails, long exposures, storm, meteor shower, exposure time, meteor storm, time exposure, star trail, Leonid meteor, Leonid meteor storm, North America, long time exposures, prime radiant, special long exposure, northeastern north america, digital camera, dark, film speed, mode, exposure mode, eastern sky, Canon EOS, Leonid meteor shower, brighter meteor trails, Canon D30, dark sky, dark skies, shutter speed, great meteor storm, clear skies, weather, good idea, time exposure mode, focal length, cable release