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Blog 19648

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Crunching the numbers



Having completed the excellent and free Future Learn - Open University short course - 'Data to Insight' (University of Auckland) I finally got around to doing something with the copious amounts of data churned out by my SDR LVST (The Lowestoft Very Small Telescope) meteor catcher. I decided to first apply my 'forensic intellect -Dr Lecter'🤓 to the 2016 Perseid Shower (I had a set of data collected from the 4th to 16th of August). 

Having done a bit of reading - an American paper from the 1990s - 'Statistical properties of meteors from a simple passive forward scatter system' by D D Meisel & J E Richardson  and the excellent - Detection & Analysis of Meteors by RADAR (Using the GRAVES space surveillance transmitter) by Dr David Morgan 2011, I decided to have a go at 'gaining some insight from the data', even though I'm more at home with a sketch book than a calculator.  As I'm fully aware that many SGL members are former scientists and engineers - please be gentle with me and some of the 'broad -brush' simplifications and approximations I have made.  I'm quite prepared to believe that I have made many school boy errors both in principle and detail!

I have organised the data using the accepted categories for meteor reflections - Over dense O, Under dense U and Transition T. 

I have filtered and manipulated the observations to create data sets:

  • O+U (including T) Cleaned source set)
  • O-T (O excluding T) Subset
  • U+T (excluding O) Subset 
  • O+T (excluding U) Subset

Creating the subsets was all a bit hit and miss and the procedure developed on an iterative basis. (As my partner is often known to say about my more off centre ideas "It might be getting a bit Goldilocks and the Three Bears")

The 'full monty' including my interpretation of the data is on my LVST site:


The following extract from the LVST relates to O+U data:

Filtering the full set of reflection observations O+U by removing all data where maxpower x duration (energy) <250 to create a new subset O+T

The graph of reflection observations O+T plotted against the (24 hour) day date indicates :


Overall the period during which data was collected 18,887 reflections were recorded.  This is  57.7% of the total number of reflections observed and represents only those reflections having a maxpower x duration =or>250 cycles (approx 3 secs).
With 95% confidence:
 The maximum number of observations - between 16.87 and 17.96 % - were recorded on the 6th August.
Between 11.53 and 12.46 % were recorded on the 7th of August.
Between 10.89 and 11.8 % were recorded on the 10th of August.*
The minimum number of observations - between 3 and 3.55 % occurred on the 4th August.
*note: because of the small over lap between lowest and highest values on the confidence bars for the 7th and 10th. we cannot be 95% confident with regard to relative values of observations between these two days.  

The graph of  reflection observations O+T plotted against the hour of the day (UT) indicates with 95% confidence :

One max peak, a smaller peak, a approximately even base line and one trough in observations: 
Max peak (approximately 5.5% of all observations)  between 2:00 and 8:00 UT.
A smaller peak between 14:00 and 17:00 UT.
A base line (approximately 4% of all observations)  at 0:00 and between 9:00 - 13:00 UT.,
A deep minimum between 18:00 and 22:00 UT

The plot of days against radial velocity for the O+T subset of observations is interesting in that it shows outliers of observations, particularly on 7th and 14th of August, grouped around radial velocities lower than the mean radial velocity (+367 m per sec with SD = 131.8) for the O+T subset.

For the Observations O+T the plot of Observations per day against Observations per hour coloured to show differences in radial velocity is interesting. To aid clarity and understanding the data has been 'binned' on a hexagonal basis. The size of the hexagon is proportional to the number of observations.
The observations made between 14:00 and 1900 (UT) on the 7th of August indicate a large number of reflections with radial velocities well below the mean value for V. The timing of these observations in the afternoon is also at odds with other days where observation density clustering is clearly skewed to the morning. Do these factors reinforce the hypothesis that a stream other than the Perseids is being detected? Could this be an outlier from the Capricornids or the Alpha Capricornids streams which are active into August?

The same observations coloured to show energy (maxpower x duration) indicate the reflections in the afternoon of the 7th of August have a greater proportion of lower energy reflections. The Capricornids are slow moving meteors and have lower velocities (lower energies?) as well as having velocity vectors different  from the Perseids.

I hope to analyse more of the data I have stored on pen drives and hopefully make comparisons between different showers and the same showers year on year. Even now I'm retired, I still seem to run out of time! 🙄








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