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 2008 Delta Aquariid Meteor Shower
• Viewing Activity from the 2008 Perseid Meteor Shower
• 2008 Meteor Shower Calendar
• Explanation of the 2008 Meteor Shower Calendar
• 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.

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 obserevers. 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 42 cents per issue). To subscribe contact our section coordinator Robert Lunsford.

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Viewing Activity from the 2008 Delta Aquariid Meteor Shower

This chart represents plotted Delta Aquariids (arrows) seen from 40 degrees north latitude while facing south near 3:00 a.m. local daylight time on July 27. This chart was created using SkyChart III Version 3.5.1 from Carina Software.

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This chart represents plotted Delta Aquariids (arrows) seen from 20 degrees south latitude while facing south near 3:00 a.m. local daylight time on July 27. This chart was created using SkyChart III Version 3.5.1 from Carina Software.

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The Delta Aquariids (SDA's) are the strongest southern shower active during the northern hemisphere's summer months. The Earth encounters these particles from July 12 through August 19 with a broad maximum occurring near July 28. Zenith hourly rates (ZHR's) average 20 near maximum activity. During July and August this radiant is well placed as it rises near 2200 local daylight time and culminates at 0300 local daylight time (LDT). This shower is visible over most of the Earth but those observers located in the southern tropical areas are best suited as the radiant passes through their zenith. Observers further south may have a lesser zenith angle but they also enjoy a longer night which allows longer observation of this activity.

On July 27, the radiant is located at 22:36 (339) -16. The area of the sky is located in southern Aquarius, four degrees west of the 3rd magnitude star Delta Aquarii. An easier signpost may be the bright first magnitude star Fomalhaut (Alpha Pisces Austrinis), which lies fifteen degrees to the southeast of the SDA radiant. These meteors strike the Earth's atmosphere with a velocity of 41 kilometers per second. Visually these meteors would appear to possess a medium speed for those shower members seen far from the radiant and high in the sky. Those seen close to the radiant or close to the horizon would appear to move slower. Most members of this shower are faint so rates seen from urban locations would most likely be unimpressive. Only from darker rural locations can this shower really be appreciated.

To view this shower it is advised that you limit your session to the morning hours when the radiant has achieved sufficient altitude. The best rates will occur near 0300 LDT when the radiant lies highest in the sky. You should face toward the southern half of the sky so that you may be able to better distinguish the SDA's from the other weaker radiants active in this same general portion of the sky. Facing this direction will also allow you to experience the swift Perseids shooting into your field of view from behind. Although not as numerous as the SDA's in July, the Perseids will provide some memorable bright meteors as you patiently wait for the fainter Aquarids to appear. In late July the moon will reach its last quarter phase on the 25th. On the morning of maximum activity for the SDA's the waning crescent moon will rise near 0200 LDT, depending on your exact location. The moon will be bright but if you keep it out of your field of view you will be able to obtain successful observations of the Delta Aquariids.

Be sure to share your data with our section coordinator Robert Lunsford.

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Viewing Activity from the 2008 Perseid Meteor Shower

This chart represents plotted Perseids (arrows) seen from 40 degrees north latitude while facing north near dawn on August 12. This chart was created using SkyChart III Version 3.5.1 from Carina Software.

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This chart represents plotted Perseids (arrows) seen from 20 degrees south latitude while facing north near dawn on August 12. 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 full moon on July 18 will deter most meteor observers from observing at this time so a majority of these early Perseids will go unnoticed in moonlit skies. Not until later in the month, when the moon reaches last quarter, will observers again venture outside to view the increasing meteor activity. Their main target at that time will not be the Perseids though, as most eyes will be gazing southward to view the activity located in that portion of the sky occupied by the constellations of Capricornus and Aquarius. These meteors will be much more numerous than the Perseids but chances are they will appear as dim and short meteors. Those occasional bright and colorful meteors shooting out of the northeastern sky will be much more impressive and memorable. They are also a sign of exciting times ahead as the Earth moves closer to the central portions of comet 109P Swift-Tuttle.

As the moon exits the morning sky in the last days of July, 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 approaches 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 folks 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. 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.

As we enter August the waxing crescent moon enters the evening sky and progresses eastward with each passing night. The illuminated portion of the moon also increases with each night as it moves away from the vicinity of the sun. As the illuminated portion of the moon increases, the lunar glare becomes a problem limiting the number of faint stars and meteors seen. This is not a problem during the evening hours as Perseus lies low in the northern sky during this time of night, producing only 1-2 meteors per hour even if the moon was absent. The moon reaches its first quarter phase (half illuminated) on August 8. On this date it will set near midnight local daylight time (LDT). Between now and the date of maximum activity (August 12), once the moon sets it's time to concentrate your efforts on the Perseids. The Earth is predicted to pass closest to the core of P109 Swift-Tuttle near 1200 Universal Time on August 12. This timing favors the Pacific coast of North America. If the maximum occurs early then continental North America is favored. If it's late then Hawaii and the eastern Pacific is favored.

With the moon being situated well south of the celestial equator, it will set far earlier for those situated in high northern latitudes. On August 12 the waxing gibbous moon will set near 0100 local daylight time (LDT) for those situated near latitude 50N, 0230 LDT for those situated near latitude 25N, and near 0330 LDT for those viewing on the equator. You can start viewing an hour before moonset as the glare from the moon will be significantly diminished as it sets in the southwest. Just be sure to keep the moon at your back so that you are looking toward the darker portions of the sky. At this time of night the hourly rates for the Perseids will still be low, perhaps 10-20 shower members per hour, depending on the transparency of your sky. 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.

On the morning of maximum activity (August 12) most of us will see the highest hourly counts between 4 and 5am. I would estimate these rates to be near 75 for those under transparent rural skies. Those under dark but hazy skies should still be able to see 40-50 Perseids per hour. Those under urban skies will be lucky to exceed 25 per hour. If your skies are cloudy on the morning of the 12th, impressive number of Perseids can still be seen on the mornings just before the maximum and after the maximum. Unfortunately the lunar interference becomes worse as you approach the full moon on August 16.

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 star count areas and the resulting equivalent limiting magnitudes are available online from the IMO web site at: http://www.imo.net/visual/major/observation/lm

It is also necessary to classify each meteor seen. On August 12, 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. Other parameters that can be recorded are the magnitudes of each meteor, the color, the velocity (slow, medium, fast) and whether the meteor produced a persistent train. If you do decide to record data, be sure to share it with us by mailing your data to our Meteors Sections Coordinator Robert Lunsford at: 1828 Cobblecreek Street, Chula Vista, CA 91913-3917. Robert also gladly accepts observations by email at: lunro.imo.usa@cox.net

This is the last time you will be able to view the Perseids under moonless skies until 2010. Next year's shower will peak with a bright last quarter moon in the morning sky, which will dampen the display. The remaining major showers of 2008 are also spoiled by bright moonlight. Not until the Quadrantids of January 2009 will a major shower peak under favorable conditions. So take every opportunity to view this display and to share your observations with us.

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Additional On-Line Resources (Provided by the American Meteor Society)

• Frequently Asked Questions about Meteors and Meteor Showers, a FAQ sheet containing more in-depth information on this topic.

• Robert Lunsford's Weekly Meteor Outlook, a weekly newsletter describing the meteor shower activity for a given week.

• Fireball Reporting Form, Report exceptionally bright fireballs.

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Comments and Questions may be directed to the Meteors Section Coordinator: Robert Lunsford

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Last Modified: July 5, 2008