Introduction :

For a general introduction to meteors see this page

The previous predictions posted earlier on on this page did not mention the presence of 2 Leonid trail in the vicinity of the Earth in Nov. 2009. There are indeed the 1466 trail and the 1533 each causing an outburst at roughly the same time (Nov. 17/11/2009 at 21:50 UT). In addition, the 1567 trail might cause a slight enhancement of activity on 17/11/2009 at 7:27 UT Below are the details for each trail.

The situation in 2008

Given the result of the 2008 Leonids campaign we can re-consider the predictions of the 2009 Leonids caused by the 1466 trail. The revised post-prediction for 2008 were the following:

Observations show that the maximum occured ~1hr later than expected, meaning that the trail was not located where we thought it was. The ZHR was close to what was forecasted. Note the high f_M value, coming from the perturbations of the planets, and Jupiter in particular.

The Situation in 2009

The general location of the streams is illustrated below

A closer view is provided below. As can be seen there is an encounter with the 1466 and 1533 trails on Nov 17th.

Detailed Results

1466 Trail

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:

f_M is less than in 2008 but the trail will be much closer to the Earth, explaining why we expect a quite high ZHR. Initially our expectations were much higher though (Vaubaillon et al 2005b). The recent analysis is based on the revised version of our program, taking into account the observations in 2008. In particular, the time of maximum may be later than expected, as in 2008. The work by E. Lyytinen and M. Nissinen (WGN, 37:4, Aug 2009, 122-124) also predicts a shower at this time and this level of activity. This plus recent changes in our code motivated us to completely re-do the Leonids forecastings, hence the change since last year. However the discrepancy between the expected time of maximum remains, as well as a general higher expected ZHR. Among the possible explanations are: sensitivity to initial conditions (given that the trail is 16 Rev. old) or change of cometary activity (impossible to verify unfortunately).

1533 Trail

This trail will encounter the Earth at almost the same time as the 1466 trail

The circumstances of the encounter are the following:

So the 2 trails will peak together for a total ZHR ~ 200/hr

1567 Trail

This one will pass further away from the Earth but may producea noticeable activity

Conclusion

The year 2009 will not see a Leonid storm, but an outburst for sure. There are still some uncertainties regarding the time of maximum of the 1466 trail [Nov. 17th 2009, 21:43 UT (+1hr?)]. The total level of the shower (ZHR~200/hr) was callibrated using the 2008 observations of the 1466 trail, but nothing is known from the 1533 trail. As a consequence, it will be very interesting to check:

Our colleagues from MSFC (D. Moser and B. Cooke) pointed out that the best location to view the outburst caused by the 1466 and 1533 trails will be centered around India and includes: Nepal, Thailand, Western China, Tadjikistan, Afghanistan, Eastern Iran, South Central Russia etc.