Nov 16/17 Meteors and the Peak of the Leonids November 17, 2008
Posted by Carl Hergenrother in Meteor Outburst, Meteors.Tags: astronomy, leonids, Meteor Outburst, meteor storm, Meteors
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In yesterday’s “The November Meteor Storms – Part II – The Leonids” posting, it was mentioned that there were a few chances for elevated activity last night for Europe and Asia. Mikhail Maslov predicted a high rate of Leonids for an hour or so on either side of 00h 22m UT on November 17. Jérémie Vaubaillon also predicted elevated rates of Leonids centered at 01h 32m UT on November 17. According to Vaubaillon, the high rates would be due to the Earth crossing a trail of dust released by Comet Tempel-Tuttle in 1466.
According to the International Meteor Organization’s Leonids 2008 Live webpage, a nice outburst of Leonids was observed at ~02h 00m UT on November 17. Based on the Leonids Live page and posts to the Meteorobs list at Yahoo Groups, observers in Europe and Israel witnessed the outburst. Rates may have reached as high as ZHR=~130.
By the time the Leonids were visible from the United States, the outburst was over. The 23 Leonids seen by my Tucson-based camera show that no outburst was visible over Tucson. Bob’s tally of 30 Leonids over San Diego also confirms this. Comparing video rates with naked eye observeing rates is tricky. Last month, when my camera detected roughly ~23 Orionids in a night, the visual observers were measuring ZHRs (zenithal hourly rate) of 10-20. So, with a bit of hand waving, the Leonids were falling at a ZHR of 10-20 over the western US last night. This is the expected rate for the Leonids when no elevated activity is seen. As you will see in Bob’s comments, his experience is that the Leonids will continue to strengthen till the morning of the 19th. So maybe there is more to come.
From Bob Lunsford’s notes: “The weather continues to cooperate in San Diego. I had the camera on from dusk to dawn and recorded 87 meteors. The first Leonid was recorded at 12:30 am PST and 29 more were caught the remainder of the night. That is an average of roughly 6 Leonids per hour. While Carl has mentioned the possibility of enhance rates may seen from the eastern hemisphere on the 17th, my personal data show that the strongest Leonid rates have been occurring on the morning of November 19th. We will have to see what actually happens.”
Jérémie Vaubaillon predicts the possibility of another period of elevated Leonid activity at 21:38 UT on November 18 though rates will may not be as high as those seen last night over Europe. This “outburst” will be observable over Asia.
Below are 2 movies from Tucson. The 1st shows the brightest Leonid (or meteor of any kind) observed by my Tucson-based camera last night. This doesn’t mean that there weren’t even brighter meteors observable over Tucson. My camera only covers a small fraction of the sky so I do miss a lot of meteors.
The 2nd movie shows 47 of the meteors detected by my Tucson-based camera. The camera is fixed so you can easily see the stars and the Moon moving from East to West through the field. The big white blob moving along the bottom of the frame is the Moon.
Movie of 47 meteors (includind 23 Leonids) seen by the SALSA camera over Tucson on the night of November 16/17 MST. The big bright blob in the bottom of most frames is the Moon.
Obs Date (UT) TotTime TOT SPO NTA STA LEO AMO TUS 2008-11-17 11h 33m 48 22 0 1 23 2 SDG 2008-11-17 11h 27m 87 45 6 5 30 1
TUS – Camera in Tucson operated by Carl Hergenrother
SDG – Camera in San Diego operated by Bob Lunsford
TotTime – Total amount of time each camera looked for meteors
TOT – Total number of meteors detected
SPO – Sporadics (meteors not affiliated with any particular meteor shower)
NTA – Northern Taurids
STA – Southern Taurids
LEO – Leonids
AMO – Alpha Monocerotids
The Meteor Storms of November – Part I – The Andromedids November 15, 2008
Posted by Carl Hergenrother in Meteor Outburst, Meteors.Tags: andromedids, astronomy, bielids, Meteor Outburst, meteor storm, Meteors
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Meteor showers are called “showers” for a good reason. The steady fall of meteors resembles the steady fall of raindrops in a rain shower. But similar to rain, there are times when a large number of meteors are seen and we experience a “storm”. More akin to thunderstorms, meteor storms produce very short (10-60 minute) “downpours”.
The month of November is witness to three different meteor showers that have caused major meteor storms in the past. Most years these showers are minor and produce rates much lower than last month’s Orionids. But a few times per century, the skies have opened and a storm has occurred. This post will focus on the first of the three storm producing showers, the Andromedids, or the Bielids, as they are sometimes called. This year the Andromedids have already passed. The reason why I made no mention of it before is because this shower has become a very minor shower. In fact, visual observers have had a hard time detecting it over the past century. Only in video meteor camera data has a hint of activity been detected.
The Rise, (Split) and Fall of Comet Biela
The story of the Andromedids starts with the discovery of Comet Biela, or to be more exact, the many discoveries of Comet Biela. Similar to the discovery story of Comet Encke in the Taurid Preview post, Comet Biela was found a few times before astronomers recognized it as the same comet. The first person to see the comet was Jacques Leibax Montaigne of Limoges, France, who found it on 1772 March 8. Since the comet was observed for less than a month, an accurate orbit could not be computed and the comet’s periodic nature was not recognized.
The comet was re-discovered on 1805 November 10 by J. L. Pons. During this return the comet passed very close to the Earth (0.037 AU). Enough observations were made that a reasonable orbit was calculated and some astronomers noticed the similarity between the orbits of this comet and Montaigne’s comet of 1772. But the link wasn’t definite and it would take another re-discovery to make a perfect link.
The 3rd discovery happened on 1826 February 27 when Wilhelm von Biela of Josephstadt, Austria, found a faint comet in the constellation of Pisces. Biela and other astronomers quickly noted that this comet was one and the same with Pons’ 1805 comet and Montaigne’s 1772 comet. With a period of ~6.6 years the comet was observed again in 1832. After being missed during the unfavorable return of 1839, the comet was recovered in 1845 which is when the story gets really interesting.
For a month and a half after recovery, the comet showed no sign of anything unusual. Then in mid-January of 1846, observers found a companion comet traveling along side Comet Biela. [See the post on Comet Giacobini for a recent example of a split comet.] The two comet components slowly separated over the next few months.
Drawing of split Comet Biela in February of 1846 from a 1888 book by E. Weiss.
When the comet returned in 1852, the two pieces of Comet Biela were observed once again. Due to poor observing circumstances in 1859, the comets were next expected to be seen in 1866. But the comets were never seen again and their whereabouts, or even if they still exist or not, is unknown. [A comet discovered by the NEAT asteroid survey in 2001 may be a piece of Comet Biela. Whether Comet 207P/NEAT is related to Comet Biela is still conjecture.]
The Rise and Fall of the Andromedid Meteor Shower
On the night of 1741 December 6, a large number of meteors were noted over the city of St. Petersburg, Russia and marks the first sighting of the Andromedid meteor shower. Additional strong outbursts were seen in 1798, 1825, 1830, 1838 and 1847. None of them compared to the showing the Andromedids would make in 1872.
By 1872, the story of Comet Biela had unfolded. Also by this time, the link between comets and meteor showers was well established. Some astronomers, such as Edmond Weiss whose book included the drawing shown in the last section, predicted that the Andromedids would be observable on 1872 November 27-28. And what a meteor display that was. Modern research into the 1872 storm suggest that rates reached as high as ~7000 meteors per hour, or roughly 2 meteors per second.
The orbit of the Comet Biela and the Andromedids. This orbit is valid for the 1852 return which helped produce the 1872 and 1885 meteor storms. The Earth is at its November 28 position.
Thirteen years later, another major storm was observed on 1885 November 27 when ~6000 meteors per hour were observed. At the time, astronomers thought the large number of meteors were due to the complete break-up of Comet Biela. It was suggested that the Earth must have traveled through the debris left over from the comet’s demise. But work reported by Peter Jenniskens in his excellent book on meteor showers, “Meteor Showers and Their Parent Comets“, suggests that the 1872 and 1885 storms were due to the Earth crossing the dust trails left behind by Comet Biela in 1846 and 1852. Based on the number of meteors observed, he finds that the meteor storms could be accounted for by a normal level of cometary activity. This suggests that Comet Biela did not release a large amount of dust when it broke into two. This means that even if Comet Biela not split, the Andromedids would still have stormed.
Though much smaller outbursts were observed in the years after the 1885 storm, the shower was nearly impossible to observe by the early 20th century. What happened? The Andromedid meteor shower is still out in space but its orbit has shifted an no longer intersects the orbit of the Earth. As a result, no additional Andromedid storms are possible. At least not for a few centuries when the orbit will once again be in the vicinity of Earth.
Analysis of meteors detected by video camera over the past few years found evidence of very low level Andromedid activity. The meteors were observable between November 1 and 19 with a peak on November 5. Though even at their peak, these residual Andromedids accounted for less than 1% of all the meteors observable that night. As a result, this meteor shower is more of a historical curiosity than something that modern observers can experience.
Next on our tour of November meteor storms, the Leonids…
Outburst of the September Perseids September 9, 2008
Posted by Carl Hergenrother in Meteor Outburst, Meteors.Tags: astronomy, fireball, meteor, Meteor Outburst, september perseids
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The September Perseids (SPE) are a minor meteor shower which produces a small number of meteors every year between September 5th and 17th. The shower usually peaks on Sept. 9 at a low rate of ~3 meteors per hour. That rate is only true for a dark, rural site with no moonlight. Rates of observable meteors are even lower at urban and suburban sites with lots of light pollution. So in general, this shower is usually not one to get too excited about. [Note, this shower is different from the spectacular Perseids shower which peaks in mid-August and is one of the year's highlights. Though both showers appear to radiate from the same constellation, the two showers are not related and were formed by separate comets.]
During the morning of Tuesday, Sept. 9, the SPEs were observed in outburst producing many more meteors than usual. My automated sky camera was able to detect over a dozen bright meteors, each one as bright or brighter than the brightest stars in the sky. One meteor was even brighter than Venus and was easily the brightest thing in the sky though for no more than a second. An image of this meteor can be seen above. There are few stars visible in the frame because the camera can only see stars down to magnitude +2. The triangle of faint stars near the beginning (left end of the meteor trail) is the west end of the constellation of Cassiopeia. A few other examples of bright meteors can be seen below.
SPE seen over Tucson at 1:01 MST.
SPE seen over Tucson through clouds at 1:30 MST.
Yet another SPE at 2:45 MST.
The radiant is the point in the sky that the meteors appear to travel, or radiate, from. Meteor showers are named after the constellation that contains their radiant. In the case of the September Perseids, the meteors radiate from the constellation of Perseus. The September in the name not only tells us what month the shower is visible but differentiates it from the more famous Perseids of August.
Plot of the radiant of the 2008 September Perseids.
The plot to the right shows the paths of all the detected meteors as bright white arrows with the following shape (|—>). The light gray lines are the extrapolated paths of the meteors back towards their point of origin. The meteor paths are plotted on a star chart and all of the white dots and diamonds are stars. The two symbols denoted by a circle with an X in it are two previously suggested radiants for the September Perseids. From the large number of meteor paths intersecting nearby, it is obvious that the proposed radiant in western Perseus is closer to, though not exactly at, the observed radiant from last night. My data shows the radiant at (RA = 49° and Dec = +39°).
Even though SEPs should have been observable between 8:00 pm and 5:00 am MST (3:00-12:00 UT), they were only observed between 12:30 and 4:15 am. This suggests the outburst was relatively short and lasted for only a few hours. Over the next few nights, a few more SPEs may be observable but at a much lower rate than last night’s outburst.
A suite of software written by Sirko Molau called MetRec was used to automatically detect meteors and determine their radiant.
Other observations of the September Perseids can be found at the excellent Spaceweather.com website.
- Carl Hergenrother
