(meteorobs) What do the 2008 Leonids tell us about 2009?

Tue Nov 25 13:26:25 EST 2008

Hi Daniel and the list,

The revised post-prediction for this year were the following (according 
to my model: comments from other modelers welcome ;-):

Year: 2008
Trail 1466
Nrev          =        16.000000
Time of max: 17/11/2008 at  0:54
longSol       =        234.92330
dist0 (au)    =    -0.0036831112
DeltaA        =      0.076176792
f_M           =       0.37717626
ZHR           =        132.50824

Given the 'old' age of the trail I was not 100% confident with the model 
so I did not really make a fuss of it. The trail is very perturbed and 
who knows what the comet was looking like back in those days. However 
the ZHR was close to what was expected (somewhat surprisingly). The peak 
was 1hr later than predicted, meaning that the trail was not exactly 
where we expected it to be. It also means that there should be a way to 
constrain the orbit of the comet this far back in time.

So for 2009, without (yet) recomputing the orbit of the comet and based 
on previous version of the predictions we can say:

Year: 2008
Trail 1466
Nrev          =        16.000000
Time of max: 17/11/2009 at 21:43 (probably later)
longSol       =        235.54461 (probably later)
dist0 (au)    =   -0.00044680846
DeltaA        =      0.099397543
f_M           =       0.19529458
ZHR           =        510.30341

2009 Leonids
Introduction:

Given the result of the 2008 Leonids campaign we can re-consider the 
predictions of the 2009 Leonids. The revised post-prediction for 2008 
were the following:
Year 	2008
TraiL 	1466
Nrev 	16
Time of max: 	17/11/2008 at 0:54 (UT)
Sol.Long. 	234.9233 deg
dist (au) 	0.003683
DeltaA (au) 	0.07617
f_M 	0.377
ZHR 	130 /hr

Observations show that the maximum occured ~1hr later than expected. The 
ZHR was close to what was forecasted. Note the ihgh f_M value, coming 
from the perturbations of the planet, and Jupiter in particular.
Results

The situation for 2009 is the following:

The exact same trail (1466) as in 2008 will be encountered in Nov 2009. 
The forecastings are the following:
Year 	2009
TraiL 	1466
Nrev 	16
Time of max: 	17/11/2009 at 21:43 (may be 0.5-1hr later)
Sol.Long. 	235.54461 deg (idem)
dist (au) 	-0.000447
DeltaA (au) 	0.09939
f_M 	0.195
ZHR 	500 /hr

f_M is less than in 2008 but the trail will be much closer to the Earth, 
explaining why we expect a ZHR reaching the 'half-storm' level (a storm 
is typically defined as ZHR=1000). The time of maximum may be later than 
expected, as in 2008: the whole calculation of the orbit of the comet 
has to be done before we are able to provide a time of maximum with 
greater confidence.

So 2009 will not see a Leonid storm, but an outburst that will reach 5 
times the level of the Perseids.