ALPO Meteors Section

Coordinator: Robert Lunsford
 
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.
[Image: Leonid Meteor Shower Radiant]

Contents:


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).


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).
[Image: Double Bursting Fireball]

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.


Viewing Activity from the 2008 Taurid Meteor Shower

Examples of Taurid Activity

This chart represents plotted Taurid meteors (arrows) seen from 45 degrees north latitude while facing south near midnight local standard time on in early November. This chart was created using SkyChart III Version 3.5.1 from Carina Software.


Examples of Taurid Activity

This chart represents plotted Taurid meteors (arrows) seen from 25 degrees south latitude while facing north near midnight local standard time on in early November. This chart was created using SkyChart III Version 3.5.1 from Carina Software.


The Taurids are not well known outside the astronomical community. They are not a strong shower and rarely produce in excess of ten meteors per hour, even at maximum activity. The Taurids are known for producing bright, often fireball class meteors during the last half of October and the first half of November. They appear to move slowly compared to most meteors. The sight of a bright Taurid, often fragmenting in flight, is unforgettable.

The Taurids are one of the few meteor showers that produce activity all night long. They are best seen near midnight when the radiant, the area of the sky where the meteors seem to originate, lies highest above the horizon. The radiant lies in the constellation of Aries during October and crosses into Taurus in November. During the time of maximum activity in early November, the large Taurid radiant is located in western Taurus, just south of the brilliant naked eye star cluster known as the Pleiades or the Seven Sisters. Any true Taurid meteor will trace back to this area of the sky.

There are actually two branches of the Taurid meteor shower. A southern branch peaks a week before the northern branch (November 5) and is located roughly five degrees further south. Together they can produce 5-10 meteors per hour during the first two weeks in November. Lesser rates can be seen in October and during the second half of November. It is difficult to differentiate between the two branches unless you face directly at this area of the sky.

Occasionally there are years when an extraordinary number of Taurid fireballs are observed. 2005 was one such year and there are predictions that 2008 may be another. These events are associated with the parent comet 1P/Encke and possible concentrations of material that happen to encounter the Earth in these years. We urge you to monitor the skies for the next two weeks to view the Taurid meteor shower. If you are lucky then perhaps a brilliant Taurid fireball will light up the skies above while you are out observing!


2008 Meteor Shower Calendar

Shower Activity Period Maximum Radiant Velocity r ZHR Class Moon
    Date S. L. R.A. Dec. km/s        
Antihelion Source (ANT) Nov 25-Sep 30 - - - - 30 3.0 3 II -
Quadrantids (QUA) Jan 01-Jan 05 Jan 04 283°16 15:20 +49° 41 2.1 120 I 25
Alpha Centaurids (ACE) Jan 28-Feb 21 Feb 08 319°2 14:00 -59° 56 2.0 5 II 1
Delta Leonids (DLE) Feb 15-Mar 10 Feb 25 336° 11:12 +16° 23 3.0 2 II 18
Gamma Normids (GNO) Feb 25-Mar 22 Mar 13 353° 16:36 -51° 56 2.4 4 II 6
Lyrids (LYR) Apr 16-Apr 25 Apr 22 032°32 18:04 +34° 49 2.1 18 I 16
Pi Puppids (PPU) Apr 15-Apr 28 Apr 23 033°5 07:20 -45° 18 2.0 var III 17
Eta Aquarids (ETA) Apr 19-May 28 May 05 045°5 22:32 -01° 66 2.4 60 I 0
Eta Lyrids (ELY) May 03-May 12 May 08 048.4° 19:08 +44° 44 3.0 3 II 3
June Bootids (JBO) Jun 22-Jul 02 Jun 27 095°7 14:56 +48° 18 2.2 var III 22
Piscis Austrinids (PAU) Jul 15-Aug 10 Jul 27 125° 22:44 -30° 35 3.2 5 II 23
Delta Aquarids (SDA) Jul 12-Aug 19 Jul 27 125° 22:36 -16° 41 3.2 20 I 23
Alpha Capricornids (CAP) Jul 03-Aug 15 Jul 29 127° 20:28 -10° 23 2.5 4 II 25
Perseids (PER) Jul 17-Aug 24 Aug 12 140° 03:04 +58° 59 2.6 100 I 11
Kappa Cygnids (KCG) Aug 03-Aug 25 Aug 17 145° 19:04 +59° 25 3.0 3 II 15
Alpha Aurigids (AUR) Aug 25-Sep 08 Aug 31 158°6 05:36 +42° 66 2.6 7 II 1
September Perseids (SPR) Sep 05-Sep 16 Sep 09 166°7 04:00 +47° 64 2.9 5 II 9
Delta Aurigids (DAU) Sep 18-Oct 10 Oct 03 191° 05:52 +49° 64 2.9 2 II 3
Draconids (GIA) Oct 06-Oct 10 Oct 08 195°4 17:28 +54° 20 2.6 var III 8
Epsilon Geminids (EGE) Oct 14-Oct 27 Oct 18 205° 06:48 +27° 70 3.0 2 II 18
Orionids (ORI) Oct 02-Nov 07 Oct 21 208° 06:20 +16° 66 2.5 23 I 21
Leo Minorids (LMI) Oct 23-Oct 25 Oct 24 211° 10:48 +37° 61 2.7 2 II 24
Southern Taurids (STA) Oct 01-Nov 25 Nov 05 223° 03:28 +13° 27 2.3 5 II 6
Northern Taurids (NTA) Oct 01-Nov 25 Nov 12 230° 03:52 +22° 29 2.3 5 II 13
Leonids (LEO) Nov 10-Nov 23 Nov 17 235°27 10:12 +22° 71 2.5 var III 18
Alpha Monocerotids (AMO) Nov 15-Nov 25 Nov 21 239°32 07:48 +01° 65 2.4 var III 23
Dec Phoenicids (PHO) Nov 28-Dec 09 Dec 06 254°25 01:12 -53° 18 2.8 var III 8
Puppid/Velids (PUP) Dec 01-Dec 15 Dec 06 255° 08:12 -45° 40 2.9 10 II 8
Monocerotids (MON) Nov 27-Dec 17 Dec 08 257° 06:40 +08° 42 3.0 2 II 10
Sigma Hydrids (HYD) Dec 03-Dec 15 Dec 11 260° 08:28 +02° 58 3.0 3 II 13
Geminids (GEM) Dec 07-Dec 17 Dec 13 262°2 07:28 +33° 35 2.6 120 I 15
Coma Berenicids (COM) Dec 12-Jan 23 Dec 20 268° 11:40 +25° 65 3.0 5 II 22
Ursids (URS) Dec 17-Dec 26 Dec 22 270°7 14:28 +76° 33 3.0 10 II 24
Information and Table Template Courtesy the International Meteor Organization.

Explanation of the 2008 Meteor Shower Calendar

Shower: named for the constellation or closest star within a constellation where the radiant is located at maximum activity.

Activity Period: the dates when the ZHR (Zenith Hourly Rates) are equal to or greater than one.

Maximum: the date on which the maximum activity is expected to occur.

S.L.: the equivalent solar longitude of the date of maximum activity. Solar longitude is measured in degrees (0-359) with 0 occurring at the exact moment of the spring equinox, 90 at the summer solstice, 180 at the autumnal equinox, and 270 at the winter solstice.

Radiant: the area in the sky where shower meteors seem to appear from. This position is given in right ascension (celestial longitude) and declination (celestial latitude).

Velocity: the velocity at which shower meteors strike the Earth's atmosphere. The velocity depends on the angle meteoroids (meteors in space) intersect the Earth. Meteoroids orbiting in the opposite direction of the Earth and striking the atmosphere head-on are much faster than those orbiting in the same direction as the Earth. This velocity is measured in kilometers per second.

r: The Population Index, An estimate of the ratio of the number of meteors in subsequent magnitude classes. Simply stated: the lower the "r" value, the resulting overall mean magnitude of each shower will be brighter. "r" usually ranges from 2.0 (bright) to 3.5 (faint).

ZHR: Zenith Hourly Rate, the average maximum number of shower meteors visible per hour if the radiant is located exactly overhead and the limiting magnitude equals +6.5. Actual counts rarely reach this figure as the zenith angle of the radiant is usually less and the limiting magnitude is usually lower. ZHR is a useful tool when comparing the actual observed rates between individual observers as it sets observing conditions for all to the same standards.

Class: A scale developed by Robert Lunsford to group meteor showers by their intensity:

Class I: the strongest annual showers with ZHR's normally ten or better.

Class II: reliable minor showers with ZHR's normally three or better.

Class III: showers with widely variable rates. They may be strong one year and totally inactive the next.

Class IV: weak minor showers with ZHR's rarely exceeding three. The study of these showers is best left to experienced observers who use plotting and angular velocity estimates to determine shower association. Observers with less experience are urged to limit their shower associations to showers with a rating of I to III. These showers are also good targets for video and photographic work.

Moon: the age of the moon in days where 0 is new, 7 is first quarter, 14 is full, and 21 is last quarter. Meteor activity is best seen in the absence of moonlight so showers reaching maximum activity when the moon is less than 10 days old or more than 25 are much more favorably observed than those situated closer to the full moon.