Bright Leonid captured from Ermelo, the Netherlands on November 20, 2018 at 01:45:18 UT. Camera: Canon 6D. Lens: Sigma 8 mm F 3.5 fish eye lens. The Liquid Crystal Shutter was set at 30 breaks per second.
Abstract
A comprehensive analysis of the Leonids 2018 is presented based on visual observational data sent to the International Meteor Organization and to the author. After the 2017 analysis of the Leonids a second one could be done based on visual meteor data. This article presents the results of this analysis. It seems there was a normal nodal Leonid maximum, but on 19 and 20 November there were two (possible) small outbursts of the meteor shower. On November 19 a bit higher as usual activity was recorded (ZHR ~ 12), but with unusual numbers of bright Leonids, and also on November 20 with a ZHR of 20 and also with bright Leonids.
Introduction
It is already 16 years ago that the last major outbursts of the Leonids took place. After that year outbursts were more often observed, but these were only a fraction of the strength of the big outbursts. This lasted until 2009, when a last outburst took place with a ZHR of 100. After this, it seemed to be quiet. In 2018, the author made a first analysis of the Leonids, based on visual observations from 2017. Even though there was not so much data available, there was a nice result with two possible outbursts on 17 and 20 November 2018 [1]. The results of this analysis was a reason, if there was enough data, to do an analysis on the Leonids 2018 with the available Leonid observations.
The Leonids are only sparingly visible from the BeNeLux. This has nothing to do with the astronomical conditions, but with the weather conditions. Very often it is cloudy in November. This was very different in 2018. High pressure over Northern Europe led to NO / SE winds during the period of 15-20 November. That resulted in the Benelux in four clear nights in a row between 15 and 19 November. The author for example, was able to observe the Leonids in the mornings of the 16th, 17th and 18th November for the first time since 2007!
Predictions
The 2018 Meteor Shower Calendar of the IMO [4] contains a summary of all the predictions made by various astronomers. It is interesting to see if there has been something observable visually. Table 1 gives an overview. Peter Jenniskens gives no extra activity for the Leonids in 2018 in his book [5].
Table 1. Overview of predictions for the Leonids in 2018 (from [4])
IMO’s on the fly graph
The author also looked on the IMO website at the well-known ZHR-on-the-fly curve. There, 27 observers had observed during 55 sessions, in which observations were collected for 135 count periods. The result was a graph based on 432 Leonids. The graph on the IMO website also contains an error, which is removed in Figure 1. It concerns a ZHR point at λꙨ 229.336 (12 November 2018 at 01:08 UT: ZHR 7 ~ 7 based on 0 Leonids. The graph of the IMO is based on data with a limiting magnitude of 5.0, and an assumed r value of 2.50 .
Figure 1. The on-the-fly ZHR profile of the IMO for the Leonids 2018.
Remarkable is a single ZHR point of 24 ~5 found at λ 237.699 (November 20, 2018 at 08:21 UT). This looks like an error or an observation where the radiant height is very low. However, further research shows that this is indeed an accurate observation!
Collecting the meteor data
The necessary Leonid data was downloaded via the website of the International Meteor Organization. The author also received some Leonid observations from observers who did not report to IMO.
Just like in 2017 rather few observations were done. The cause may be the bad weather conditions in November and the low activity of the Leonids. The workflow: first, of course, the available observation data were critically examined. Radiant height (observations below 25 degrees radiant height were not used), limiting magnitude (limiting magnitude 5.9 or less was not used), extreme outliers were removed and only data from observers with a reliable Cp were used.
After selecting all the data that met the requirements described above, 507 Leonids remained for the analysis. These are 201 Leonids more than for the analysis of 2017.
Leonids 2018: population index r
In contrast to 2017, a population index value could be determined for 2018 for the period from 16 to 18 November 2018 and this only based on the European data. The results are shown in Table 2. A total of 367 Leonids were used for the determination of the population index r. Because the interval r [0; 5] yields the best numbers during the three nights, meteors were chosen for that selection.
Table 2. Population index r Leonids 2017. In the ZHR calculations r [0; 5] was used.
Leonids 2018: ZHR
The ZHR was determined by the method of Peter Jenniskens as described in [2 & 3] with the radiant height correction on 1.0 instead of 1.4 to make a comparison with the IMO curve. For the nights 15/16 (maybe too low numbers), 16/17 and 17/18 November 2018, sufficient data was available for a population index r determination r [0; 5]. Values for the population index r as equal to 3.02, 2.98 and 2.53 were used respectively for the nights 15/16, 16/17 and 17/18 November. With a strong number of bright meteors during the morning of November 19, the author assumed a r value of 2.40 and for all other nights the IMO value 2.50 was used. For the ZHR determination a total of 507 Leonids could be used, this resulted in table 3 and figure 2.
Table 3. Calculated ZHR values based on 507 Leonids.
Figure 2. ZHR graph Leonids 2018 based on Table 2 (507 Leonids).
The period shown is from 4 to 21 November 2018.
There is little difference between the ZHR curves from this analysis and the IMO ZHR-on-the-fly curve (figures 1 and 2). The differences are caused, among other things, because not all IMO data has been used, data from observers have been used who do not report to IMO and an assumed population index r 2.50 has been used for the IMO curve. See also figure 3 that combines the IMO chart and that of the author. Very small differences in the first nights but in the period 16-19 November we notice somewhat larger differences.
Figure 3. Comparison Leonids ZHR 2018 between this analysis and the IMO ZHR-on-the-fly curve.
16/17 November 2018
We zoom in on the ZHR values found per hour in the night 16/17 November. This resulted in figure 4. According to the IMO Meteor Shower Calendar 2018 [4] the nodal passage in 2018 was at λꙨ = 235.27 ° (17 November 2018 at 22:30 UT). As expected, we see a slightly increasing ZHR from 8 to 12 over Europe that night, these are the first four ZHR points. This European part of the graph is based on 93 Leonids (12 periods, 7 different observers). This mainly concerns weak Leonids, but it is striking that several observers also see a relatively large number of 0 to -3 Leonids, few of +2 but again a lot of +3 and +4.
We see declining ZHRs over the American continent. However, caution is required here, it concerns three ZHR points based on only 2 individual observers, namely Terence Ross (5th ZHR point) and Wesley Stone (6th and 7th ZHR points).
Figure 4. ZHR Leonids in the period November 17, 2018 between 01 and 13 UT.
17/18 November 2018
Of course we also zoom in on the ZHR during this night. As mentioned earlier in this article, nodal passage took place on 17 November at λꙨ = 235.27 ° (17 November 2018 at 22:30 UT. The ZHR above Europe (the first 6 ZHR points) decreases from 15 to 10- 13, exactly what was to be expected. The first point above America seems to be high, the other three are more in line with what to expect.
Figure 5. ZHR Leonids in the period November 18, 2018 between 00 and 13 UT.
Outburst Leonid activity in 2018?
After the maximum night of November 17/18, we enter the “interesting area” of the Leonids [4]. Unfortunately, the weather barely cooperated. There are few Leonid data in the IMO database after November 18th. There are three observations of “suspicious” Leonid activity.
18/19 November 2018
Only one observer could observe in this night. Michel Vandeputte reported relatively high activity of bright Leonids. He wrote:
At 01:45 UT I was installed in the backyard and tsjakka: immediately an impressive -2 Leonid with persistent train moving to the southern parts of the sky! Immediately countered by a not much less beautiful -1 sporadic meteor from Canis Minor. More of it please! Here and there, there was a small cumulus-cloud, but they did not really bother. I could observe for two hours before the clouds re-appeared. The night sky was better at times than last night: more transparent and less hectic. But the wind blew a lot more and it felt pretty cold. The Leonids were much more attractive to my surprise! A whole battery of nice bright meteors between -2 and +2, certainly hour counts of 10. Only in the end of my session the activity decreased a bit.
For those two hours a ZHR is calculated of 12 ~ 4 with an assumed population index r of 2.40. The ZHR found is somewhat higher than the American ZHR values from figure 5 of November 18, 2018. The magnitude distribution is also strange, see table 4 below. Unfortunately, Michel was the only observer who observed this event. The lack of weak Leonids is striking with as a result the high average magnitude of 1.15.
Table 4. Observation of the night 18/19 November 2018 by Michel Vandeputte.
Vandeputte’s observation is supported by radio observations published by Felix Verbelen, he wrote the following on the VVS mailing list:
Yesterday (20181118) it seemed that the Leonid activity this year would be moderate … Not so. Today, since 01h UT, many strong and long-lasting reflections! Attached are some eye-catchers on the frequency of our VVS beacon (49.99 MHz), here in Kampenhout.
If we look at the graph of overdense reflections longer than 10 seconds of Felix (figure 8) then we see indeed an increasing activity in the nights 16/17, 17/18, 18/19 and 19/20. Although the ZHR was lower in the night 18/19 than in the previous night, the number of bright Leonids turned out to be higher on the night of November 18/19 than on the previous night. See also Felix’s article in Meteornews [8].
A second confirmation of the nice activity of bright Leonids on the morning of November 19 was on the well-known website of Hirofumi Sigumoto (figures 6 and 7). The way in which Sigumoto performs his calculations is described in Meteornews [6]. The prediction of Jeremy Vaubaillon is the closest to this particular observation. So perhaps Michel has seen some activity from the associated dust trail.
Figure 6. Leonid ZHRs determined based on radio observations from RMOB [6].
Figure 7. A part of the Leonids radio ZHR curve of Hirofumi Sugimoto, combined with the visual data (ZHR) by Michel Vandeputte. The graph suggests that there may have been some more Leonid activity in the period before Michel did his observations.
Figure 8. Graph based on radio observations of the Leonids by Felix Verbelen of all overdense reflections longer than 10 seconds. These can be best compared with visual data because of the bright meteors.
November 20, 2018
In both the IMO ZHR-on-the-fly graph (Figure 1) and the graph of this analysis (Figure 2) we see the fairly high ZHR point around November 20 (λꙨ 237.80). This appears to be a ZHR point based on an observation reported by the active American observer Terrence Ross. His observation was done from Alpine, Texas on November 20 between 10:26 and 11:30 UT with a radiant height of 62 degrees. It yields a ZHR of 20. His observation can be found here:
https://www.imo.net/members/imo_vmdb/view?session_id=77963
The number of bright Leonids is also striking, somewhat comparable to the observation by Michel Vandeputte of November 19, 2018. Unfortunately, Ross is the only observer who has observed this.
However, there is another observation that was done earlier on the 20th by Pedro Pérez Corujo from the island of Cran Canaria. His observation can be found here:
https://www.imo.net/members/imo_vmdb/view?session_id=78032
His observation could unfortunately not be used in this analysis because of the too low limiting magnitude. But because of Ross’s observation, it is used to compare the observations. Corujo sees 12 Leonids with a limiting magnitude of 5.5 between 05:15 and 06:15 UT and a radiant height of 70 degrees. This yields a ZHR of 33 ~ 9.7. Unfortunately, this observer did not provide any magnitude distributions. His observation is roughly 5 hours before the observation of Ross and seems to be an indication that a possible small outburst was going on at November 20th.
The observations of Ross and Corujo are also supported by the graphs of Hirofumi Sugimoto (Figure 9) and Felix Verbelen (Figure 8). The ZHR on November 20 was higher than on November 19 and indeed the graph of Felix Verbelen also shows higher activity on November 20 than on November 19. All three modellers Sato, Vaubaillon and Maslov give candidates fort his possible outburst: the observation of Corujo fits best with Sato (1433 dust trail), that of Ross with Maslov (1466 dust trail). The radiograph of Sigumoto (figure 6) shows two broad peaks on November 20th. It is therefore very unfortunate that not more observers were active during this period.
Figure 9. The radio ZHR graph of Hirofumi Sugamoto compared with visual observations (ZHR) from
Pedro Pérez Corujo (CORPE) and Terrence Ross (ROSTE).
Recommendations
Like the analysis of the Leonids for 2017, this analysis also shows that the Leonids between 15 and 25 November can be very interesting with sometimes small “outbursts”. Therefore, I make a call to actively observe this meteor shower visually! And also, in 2019, when the conditions are moderate because of the Moon, the shower should be monitored. Who knows what surprises we will get to see?
I would also like to urge all observers to observe more in the period at the end of July and during entire August. This way I can calculate more reliable Cp’s and add more data in the analyzes.
Acknowledgment
First of all, a huge word of thanks to the observers who observed the Leonids in 2018. These are: Alexandre Amorim, Shrinivas Aundhkar, Pierre Bader, Steve Brown, Tim Cooper, Tibor Csorgei, Kai Gaarder, Glenn Hughes, Paul Jones, Javor Kac, Adam Marsh, Ken Marsh, Pierre Martin, Koen Miskotte, Rafael Neumann, Pedro Pérez Corujo, Ina Rendtel, Jürgen Rendtel, Terrence Ross, Kai Schutze, Ben Sharp, Ulruch Sperberg, Wesley Stone, Hanjie Tan, Michel Vandeputte, Roland Winkler, Frank Wächter and Sabine Wächter.
A word of thanks also goes to Paul Roggemans, Carl Johannink and Michel Vandeputte for a critical review of this article and for the suggestions given. Felix Verbelen and Hirofumi Sigumoto are thanked for providing radio data and useful discussions.
References
[1] Miskotte K., De Leoniden in het off season deel 1. 2017: een kleine uitbarsting!, eRadiant 2018-2, p. 73-78
[2] Jenniskens P., Meteor Stream activity 1. The annual streams, Astron. Astrophys. 287, 990-1013 (1994)
[3] Miskotte K., Johannink C., Miskotte K. & Johannink C., eRadiant 1/1 (Feb 2005), Analyse Perseïden & Geminiden 2004, p. 9–12 & 14–19
[4] Rendtel J. et al., 2018 Meteor Shower Calendar, p. 18-19
[5] Jenniskens P., Meteorshowers and their parent comets
[6] Sugimoto H., The new method of estimating the ZHR using radio meteor observations, eMeteornews 2017-4, p. 109-110.
[7] http://www5f.biglobe.ne.jp/~hro/Flash/2018/LEO/index.html
[8] https://www.emeteornews.net/2018/12/03/radio-meteors-november-2018/
