ALPO Meteors Section

The peak of the 1998 Leonid meteor shower (rich in bright fireballs), shown in a four-hour time exposure through a fisheye lens, and taken by Juraj Toth of Modra Observatory. This photograph demonstrates how the meteors in a particular shower appear to emanate from a certain point in the sky called the radiant. On a given night, this radiant point will remain relatively stationary with respect to the background star constellations; but will rise, traverse the sky, and set in the same manner as the sun and moon.

• Viewing Meteor Activity
• Viewing Activity from the 2010 Perseid Meteor Shower
• 2010 Meteor Shower Calendar
• Explanation of the 2010 Meteor Shower Calendar
• New Meteors Book Available
• Additional On-Line Resources

Viewing Meteor Activity

Since meteors are a transient phenomena one cannot go outside at night and expect to see meteor activity. This is especially true during the evening hours when the Earth is moving in the opposite direction from the sky seen above during those hours. At this time of night meteoroids (meteors in space) must catch up to the Earth in order to enter the Earth's atmosphere. Therefore meteor rates are lowest near 1800 (6:00pm) local time. Conditions for viewing meteor activity improves as the night progresses. At midnight a great majority of the meteors seen strike the Earth from a perpendicular angle instead of from behind. These conditions offer better rates than witnessed early in the evening but the general activity is still low when compared to the morning hours. During the dark morning hours the Earth is rotating toward the direction it moves in space, known as the apex. During this time the Earth slams head-on into meteoroids and many more will be seen. This is much like a vehicle driving through the rain. More raindrops will strike the front windshield compared to the rear window. The peak meteor activity occurs near 0600 local time.

In addition to the diurnal cycle there are also annual variations in the meteor activity. As seen from the mid-northern hemisphere the second half of the year is much more active than the first six months. The reason for this are several. First of all the sporadic (random) meteor activity is stronger during this period. Also most of the major annual showers active during the second half of the year have radiants located north of the celestial equator, favoring northern observers. The cycle seen from the mid-southern hemisphere is opposite with the better activity occurring during the first half of the year. Observers at the equator enjoy fair, but not exceptional activity all year long.

During certain times of the year the major meteor showers are active and increase the nightly activity severalfold. This is especially true if the moon is near its new phase and not brightening the nighttime sky. The list of these showers is provided below (see the class I showers).

This is also the best time to see fireballs, which are exceptionally bright meteors that can light the nighttime scene. These meteors can range from the light of the brightest planet Venus (magnitude -5) to that beyond the light produced by the full moon (magnitude >-13).

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This double bursting fireball was photographed at 23:45 Universal Time on August 6, 2007 by Maurizio Eltri from central Venice, Italy. He estimated this sporadic (random) fireball to be of maximum magnitude -8, which is nearly as bright as the half moon. Picture courtesy of Maurizio Eltri, (Unione Astrofili Italiani Sezione Meteore).

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To keep current on the upcoming meteor activity the Meteors Section invites you to subscribe to their quarterly newsletter, available for the price of postage (currently 44 cents per issue). To subscribe contact our section coordinator Robert Lunsford.

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Viewing Activity from the 2010 Perseid Meteor Shower

This chart represents plotted Perseid (arrows) seen from mid-northern latitudes while facing east near 4:00 a.m. local daylight time on August 13. This chart was created using SkyChart III Version 3.5.1 from Carina Software.

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In mid-July the Earth begins to encounter debris released from long period comet 109P Swift-Tuttle. The particles encountered at this time travel in a path far from the mainstream orbit of debris from the comet. Their radiant (the area of the sky these meteors seem to come from) lies on the Andromeda/Cassiopeia border and only their swift velocity reveals their identity as early arrivals of the Perseid meteor shower. The moon is favorable for observing these early Perseids up to July 23, when the waxing gibbous moon will remain in the sky most of the night, obscuring all but the brightest meteors. From then until August 3rd, the moon will interfere with observing during the prime morning hours. During the first week of August the Perseids will share the spotlight with the Delta Aquariids (SDA). Both showers will be equally strong producing 5-10 shower members per hour, depending on your latitude. During the morning hours the SDA radiant will be located low in the south while the Perseid radiant will lie in the opposite direction. It will be somewhat of a battle between the two showers with them shooting meteors at each other. As the second week of August arrives activity from the Delta Aquariids will wane while the Perseids will surge in activity.

The moon becomes a non-factor by August 7th. Also by now the Perseid meteors now become more noticeable as their rates are approaching that produced by the random (sporadic) activity seen each hour. The radiant has traversed the southern portions of the constellation of Cassiopeia and now lies among the stars of Perseus. At this time of year, the constellation of Perseus (the hero and slayer of the dreaded Medusa) lies on or near the northern horizon at dusk. This is the absolute worse time to try to view Perseid activity as a great majority of the meteors occur below the horizon or are blocked by trees and hills. The occasional Perseid that does manage to shoot upward at this time of night is often a magnificent sight as it only skims the upper portions of the Earth's atmosphere. This allows it to last several seconds instead of the normal sub-second streak. The Perseids seen at this time of night will also travel in long paths adding to the impressive scene.

As the evening progresses, the stars of Perseus begin to climb higher into the northeastern sky. Just how high depends on your latitude. The further north one lives, the further the radiant will lie above the horizon. If you are located too far north though, the sun sets later and rises earlier limiting the time you have to view the activity. For those located south of the equator, the Perseids are strictly a post midnight affair, as the radiant does not clear the horizon until the morning hours. For those located south of 35 degrees south latitude, the Perseids are not visible at all as the radiant never clears the northern horizon. So those situated near 30 degrees north latitude probably enjoy the best combination of high radiant altitude and long nights in which to enjoy the display.

As the midnight hour passes the Perseid activity begins to kick into high gear. The radiant now lies high enough above the horizon from most locations to allow meteors to be seen shooting in all directions, including straight down. To see the most activity it would be advisable to view approximately half up in the sky with the radiant toward the edge your field. Personally, I like to view above the radiant at this time and then have it move through my field of view as the night progresses. This basically means that I face northeast at an altitude of 45 degrees the entire night. I was never one that wished to get out of a warm sleeping bag to move my chair in the middle of the session!

The best Perseid activity, no matter the date or location, is usually seen during the last hour before the start of morning twilight, when Perseus lies highest above the horizon in a dark sky. This is usually between the hours of 0400 and 0500 local daylight time for most of us. While gazing high into the sky, one must be comfortable in order to avoid neck strains and fatigue. A folding lounge chair is the perfect solution. It is easily portable and comfortable. Be sure to also have a blanket or sleeping bag too, even if temperatures seem balmy. It's surprising how the inactive body can become chilled even though the air temperatures seem warm.

The Earth is predicted to pass closest to the core of P109 Swift-Tuttle near 0100 Universal Time on August 13. This timing favors western Asia. Both the mornings of August 12 and 13 will be good for North America, with perhaps the 13th offering slightly more activity due to the fact we are closer to the predicted time of maximum activity.

On the mornings of August 12 and 13, I would estimate peak rates to be near 60 for those under transparent rural skies. Those under dark but hazy skies should still be able to see 30-40 Perseids per hour. Those under urban skies will be lucky to exceed 20 per hour.

Transparency is an important factor as many of the Perseid meteors are faint. A hazy, humid night can hide these faint meteors making the display seem much weaker than it actually is. This haze also scatters light from ground fixtures, making it difficult to view the display from urban areas. It is difficult for those in the eastern half of North America to escape this haze. Their only recourse is to find a safe rural site away from urban lighting. This will help with the problem of scattered surface light but not the dimming of the stars above. Observers in the west often have the ability to travel to mountain sites above the haze where one can see the stars and meteors right down to the horizon.

The characteristic Perseid is a bright white or yellow meteor lasting less than a half second. The brighter meteors usually leave a persistent train or "smoke trail" that lasts a second or two after the meteor has vanished. This is not really smoke at all but rather ionized gas created by the meteor passing through the atmosphere at tremendous velocities.

One of the best times to try and photograph meteors is during the Perseid meteor shower. All you need is a camera capable of exposures lasting one minute or longer. Simply aim the camera high enough to clear the horizon and set the focus to infinity. Don't aim the camera straight up as this is the worst direction for meteor activity. The layer of air directly above you is the thinnest therefore less activity will be seen there compared to the denser portions of the atmosphere located closer to the horizon. Also try to center the camera 30-60 degrees from the radiant so that the meteors are long enough to be easily seen on your photograph. Meteors appearing near the radiant will appear shorter as they are traveling in a direction toward you. It is also advisable to use the fastest film/ ISO setting possible to increase the sensitivity of you camera. Meteors will appear as straight streaks overlapping the curved trails created by the stars moving through the field of view. The length of the star trails will depend on the length of your exposure and the direction you point the camera. Pointing your camera northward will decrease the length of the star trails. Some photographers eliminate the stars trailing by mounting their cameras on motor driven mounts. With this setup the stars remain as pinpoints while meteors are obvious streaks.

It is also enjoyable and scientifically useful to record the meteor activity you see. Experts in meteor astronomy can reduce your data and compare it to others all over the world if you use certain standards in your reporting. First and foremost is to provide the accurate time of your observing session. It is helpful to time each meteor but not absolutely necessary as long as the start and finish times are provided. The observing conditions are very important to properly record, especially if your field of view is obscured by clouds or trees. These obscurations should be recorded to the nearest ten percent. Once per session is fine for trees but at least every 15 minutes for changing conditions such as cloudiness. The limiting magnitude of the sky in your field of view should also be recorded at least once an hour. The easiest way to do this is to count the number of stars visible in pre-selected areas of the sky. These areas and the resulting limiting magnitudes are available from the IMO web site at: http://www.imo.net/visual/major01.html#table2

It is also necessary to classify each meteor seen. On August 13, a majority of the meteors seen will be Perseids. There is no way that every meteor is a Perseid that night. There are on average 5-10 random meteors occurring each hour. These can come from any direction and be of any velocity, usually slower than the Perseids. Perseids will always line up with the radiant in Perseus and will usually be swift unless they occur close to the radiant or close to the horizon. There are also minor showers active during the Perseids that will also add a few meteors per hour to the total count.

If you would like to contribute more to our knowledge of the Perseids then I invite you to get serious about meteor observing and to make an hourly count of the activity you witness. Other more detailed projects include the estimating the magnitude, velocity, and color of each meteor. Others also note whether there was a persistent train after the meteor has vanished. Meteor watching can be both fun and scientifically useful endeavor. To be scientifically useful you must share your data with an active meteor organization such as ALPO. We accept data from observers with all levels of experience. Our data is published in our quarterly newsletter. The easiest way to share your data is to email your results to our section coordinator Robert Lunsford. We look forward to hearing from you!