PERSEID 2002- Monitoring the Moon for Meteoritic Impacts
 
 

By Raffaello Lena (a), Stefano Basso and Feliciano Villares (b)

(a) Coordinator for ALS Lunar Impact project (gibbidomine@libero.it)

(b) GLR group

Introduction

Several attempts have been made to obtain scientifically valid lunar impact observations, one of the most notable being by Association of Lunar and Planetary Observers (ALPO) [1].

For the first time, independently confirmed observations of meteoritic impacts on the Moon were recorded during the meteor storm of November 18, 1999 [2-3] .

Recently, many lunar observers and amateur Associations have shared their plans for the observation of lunar meteor impacts from the Perseid meteor shower.

This paper is based on the analysis of observational reports (from European Observers) submitted to the ALS coordinator for the computed dates described in Table 1.

Table 2 lists the observers, instruments and location.
 
 

Table 2
 
 

Contributing individuals and instruments for computed dates, where

(a ) is August 12  , 2002 (b ) is August 13 , 2002 and (c ) is August 14, 2002.

(*) Observer used an approximate timing (+/-2 min)
 

Observer	telescope  D e F/D	type	date and time (UT)	N° of flashes
Basso S. (Valcava-Lecco) Italy	Newton  114 mm f/8	Webcam	(a) 19:19:36- 19:39:36 19:44:00- 20:00:00 (b) 19:17:53- 19:18:13 19:20:00 - 19:26:30 19:28:30 - 19:48:30 19:49:40 - 20:09:40	3 0 0 0 0 0
Cook J. (Essex) UK	Dobson 200 mm f/5	Visual	(a) 19:00 -20:00 (*)	1
Lena R. (Leonessa-Rieti) Italy	Newton  114 mm f/8	Visual	(a) 18:25:00- 19:07:50 (b) 19:50:00- 20:05:00 (c) 18:44:00- 18:55:00	0 0 0
Villares F. (Valencia) Spain	Refractor 120 mm f/8	Video cam	(a) 19:44:00 -21:15:15	0

 

Instruments and Measures

A timing was preserved using a receiver tuned to station HBG, which transmits time signal at 75 KHz. A video cam and a web cam was used from two observers (Villares and Basso).

The webcam (Vesta Pro), fitted to a Newtonian 114 mm telescope, was used with exposure time equivalent at 0.004 sec (frame rate 10 fps). The acquisition of the images (AVI file) has been made using the software Qcfocus.

The video camera MK-03461E (1 lux of minimum illumination with 420 TV lines of resolution) was fitted to a refractor 120 mm telescope. Accurate locations of the flashes detected on the dark side of the Moon was obtained measuring their Limb Angle (PA) and their distance (D) from the Lunar center (expressed in Lunar radius unit). The Limb Angle (PA) is measured in direction N->W, so the north region and the mean west region correspond at 0° and 90° respectively. The flashes are reported in Table 3. Also recorded in this chart are the signal to noise ratios. The S/N ratio was calculated by measuring the distance between the peaks and troughs in the non-flash sections of the tape, as described in [4].

The reported magnitude is only a rough estimation, due to the low altitude of the Moon during the Perseid shower from Europe.
 
 

Results and discussion

As reported in Table 3 there was a number of events observed during our project.

Figures 1 and 2 show flash B and flash C respectively.

Unfortunately, none were conclusively confirmed by simultaneous observations. A group of astronomers in Spain (Instituto de Astrofisica de Andalucia, CSIC Granada) did not record any flashes at the same times or even some seconds earlier and later. Ortiz [9], using also a large telescope (1.2 m. infrared observations) cannot confirm any flashes detected on 12 august 2002.

Figure 1- Flash B detected by S. Basso (12 August 2002 at 19:24:35 UT)
 
 

Figure 2- Flash C detected by S. Basso (12 August 2002 at 19:29:11UT). It is visible in one single frame.

The faint flash A (not reported here) has a low S/N ratio and it , likely, is a noise peak due to effects from electronic components. Furthermore, flash C could be a cosmic ray signature. However flashes A and C appear only in one single frame (Table 3).

On the contrary flash B appears in at least 3 frames. It is present in a stationary position (Centroid coordinate X= 403.49 Y=259.85) , which again rules out artificial satellite glints (these are always trailed and appear on many frames). Besides, we checked the positions of all geostationary satellites, and no one was closed to the Moon as seen from Valcava at the states time. The Moon was 4° north of the geostationary satellite "band" as seen from Valcava, Latitude 45° 47' 05" N Longitude 9° 30' 45" E 260 m over the sea level, at the stated times (USNO communication) [8].

On the same date, J. Cook reported us a very bright flash (magnitude was estimated at about 1) approximately at 19:27 UT +/- 2 min. (private communication). Due to the orientation of the Moon at low altitude from England, Cook considers the location of the flash he saw to be compatible with the north of Mare Frigoris (compatible to our flash C) . Considering the approximate timing reported by the English observer and the negative results from the Spain we cannot have any independent confirmation.

Because spurious flashes can occur due to the various reasons listed in our preceding papers [4-7], it is clear that a videotape of a flash (e.g Flash B not confirmed), which is restricted on one single videotape obtained by a single observer, is an insufficient evidence to prove that a lunar impact has occurred.

However the spurious flash B appears in at leat 3 frames (similar to an afterglow) whose nature is still unclear to us.

It has already reported in [4-5] that it very difficult to differentiate between what can be a real flash and what is a spurious flash. On the other hand, in a preceding paper [5] the authors (Lena and Favero) strongly encouraged observers to defocus the image recorded by the video camera or to place a dispersing element in front of the CCD; this rules out electronic noise or cosmic rays (methods for a single observer to validate the impact origin of the recorded flash).

Furthermore an important cooperation was obtained, so that the program shows promise for positive results in the coming years.

It is important that at least more experienced observers take part in this combined effort. Lunar Observers are encouraged to monitor the Moon during Meteor showers in order to support the ALS project.

We thank J. L. Ortiz for very helpful comments and his stimulating discussion.
 
 
 
 

References
 
 

[1] Williams, Thomas R. , JALPO, 2000, vol 42.4

[2] Cudnick, Brian, JALPO, 2002, vol 44.1

[3] Dunham, David W. et al, 2000, paper 1547 , Lunar and Planetary Science Conference XXXI, Houston Texas

[4] E. Douglass, F. Badalotti, G. Venturin, R. Lena, and G. Santacana, 2001, JALPO, vol. 43, n. 2, p. 24-29

[5] R. Lena and G. Favero, Selenology, 2002, vol 21.2

[6]R. Lena, Selenology, 2001, vol 20.3

[7] R. Lena, Selenology, 2002, vol 21.3

[8] Private communication, G. Chester USNO Public Affairs Office.

[9] Ortiz J. L. , Instituto de Astrofísica de Andalucía, CSIC Granada, Spain (private communication) .