Abstract: Examination of archived sporadic meteor orbits from the UKMON multi-station meteor survey suggests a summer shower centered in Lacerta.


Archival data from the UKMON meteor survey (e.g. Campbell-Burns and Kacerek, 2014) were obtained from the UKMON online public data archive and all the orbits flagged as being sporadic retained whilst all other orbits were removed, leading to 16252 remaining orbits.  The orbital part of the data was then analyzed against a copy of itself for all 16252 orbits utilizing the Jopek (1993) D criterion modification, henceforth referred to as DJ, to obtain matching orbit pairs using a DJ upper threshold limit of 0.10.  This particular processing time took over four days on a 3GHz intel quadcore computer.

The resultant output was examined for radiant clustering via passive visual inspection of the radiants’ positions plotted against the sky with solar longitude and geocentric velocity being scaled into the graphical representation.  Following on from this some indication of a reasonably tight but thinly populated grouping was noted in Lacerta and accordingly a wider DJ test was made upon the mean orbital particulars of those meteors using data from multi-station meteor survey publicly available data archives of SonotaCo Network (e.g. SonotaCo, 2009), CAMS (e.g. Jenniskens et al., 2018) and EDMOND (e.g. Kornoš et al., 2014) and Global Meteor Network (Vida et al., 2019a; 2019b).  As various regional meteor surveys can not only provide their own dataset but contribute it to other surveys the combined datasets used in this search had the potential for some duplicates, accordingly the results were sorted on Right Ascension and any objects in the resultant output having a commonality of Right Ascension, declination and solar longitude had their duplicates removed.  This led to the removal of one orbit, with one other orbit being removed as its orbit had a hyperbolic solution. A new mean orbit was then derived from the results and that orbit further tested against the above-mentioned datasets using the DJ criterion.


The analysis resulted in a total of 21 meteor orbits meeting the DJ < 0.100 threshold, of which 13 have DJ < 0.008 and 4 have DJ < 0.006.  The meteoroids spanned the years 2009 to 2021, with 2012 the only missing year, ranging from only one some years to four each in 2015 and 2016.  However, due to the nature of the surveys used all bar one of the meteors were brighter than magnitude +1 and of these 12 were brighter than magnitude 0, essentially fireballs, with the brightest magnitude –3.4.  Thus, there is a selection effect for only the brightest of potential meteors from this shower having been detected.  The distribution of meteors as a function of solar longitude is displayed in Figure 1, and the particulars of the meteors are given in Table 1.


Figure 1 – The number of meteors as a function of λʘ (solar longitude) in degrees.


Figure 2 – The orbits of the 21 meteors depicted for a representative date of July 16th where the Earth and Sun are represented by black dots, with the Earth’s orbit shown as an ellipse and the meteor orbits shown with the above ecliptic sections in dark grey and the below ecliptic section in lighter grey.


Table 1 – Mean and Median plus standard deviation on the Mean along with Minimum and Maximum values of the meteor orbits are given for :- Right Ascension (in degrees); declination (in degrees); solar longitude, λʘ, (in degrees); geocentric velocity, vg, (km/s); perihelion distance, q, (AU); eccentricity, e; inclination, i, (in degrees); argument of perihelion, ω, (in degrees); ascending node, Ω, (in degrees); ecliptic longitude, λ, (in degrees); ecliptic latitude, β, (in degrees); ecliptic latitude minus solar longitude, λ–λʘ, (in degrees) and longitude of perihelion, Π, (in degrees).

R.A. Dec λʘ vg q e i ω Ω λ β λλʘ Π
Mean 342.3 44.1 114.0 53.5 0.935 0.922 98.5 213.4 114.0 6.3 46.5 252.3 327.5
Median 342.4 44.0 113.7 53.3 0.937 0.924 97.8 213.6 113.7 6.0 46.5 252.1 326.6
Stand. Dev. 2.4 1.0 2.6 0.8 0.013 0.033 1.6 2.9 2.6 2.5 1.0 1.5 4.5
Min 338.8 42.7 110.6 52.1 0.909 0.849 95.7 209.2 110.6 2.6 44.5 249.3 320.8
Max 346.8 46.7 118.8 54.9 0.955 0.990 101.4 218.4 118.8 10.6 48.6 255.0 335.1


The similarity of the orbits is revealed in Figure 2 where the ecliptic crossing path at a date of July 16th is depicted with the Earth and Sun shown.  Figure 3 lists the disposition of the meteors in terms of geocentric ecliptic latitude βg in Sun-centered geocentric longitude with respect to the UKMON sporadic meteor background, whilst Figure 4 does the same for the case of the meteor orbital inclinations i against the longitudes of perihelion Π.  Finally Figure 5 denotes the position of the 21 meteors in Right Ascension and declination with respect to the full entirety of the 16252 sporadic UKMON meteors used in the analysis via Aitoff projection.

Figure 3 – A depiction of the ecliptic latitude, β, with respect to the difference between the Sun-centered ecliptic longitude, λ–λʘ, for the shower meteors depicted as black filled circles and the UKMON sporadic meteor background in light grey circles.


Figure 4 – A depiction of the orbital inclination, i, with respect to the longitude of perihelion, Π, for the shower meteors depicted as black filled circles and the UKMON sporadic meteor background in light grey circles.


Figure 5 – The Right Ascension and declination of the shower meteors are shown in Aitoff Projection denoted as red filled circles with the entirety of the 16525 sporadic UKMON meteors denoted as light grey dots. Grid lines are shown for every 3 hours of Right Ascension and every 30 degrees of declination.


Examination of 16525 sporadic UKMON meteor orbits suggested a clustering of same geocentric velocity meteors in Lacerta and subsequently an iteratively derived mean orbit for an area in Lacerta was tested against an extended dataset of orbital data.  This resulted in 21 potential meteor orbits from which mean and median and standard deviation particulars of radiant, Solar Longitude, and orbit were derived.

This led to a potential shower of some small radiant dispersion but relatively tight date of presentation of around 1 to 4 bright to fireball level medium to fast meteors per annum, near a representative radiant of Right Ascension 342 degrees, declination 44 degrees centered around a solar longitude of 114 degrees (around July 16th) and a geocentric velocity of 53.5 km/s.


The meteor survey groups and especially their volunteers and operatives are expressly thanked not only for their work but for making their data public and thus available for analytical examination by all instead of just wallowing in a private archive.  The individual groups are mentioned in the body text of the article and fully referenced below.  Strangely, for the case of public domain scientific data, the Global Meteor Network (GMN) and UKMON data are released under the following licence. The Aitoff Projection was generated using TopCat.



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