Leonids

Active November 15 - 20

Radiant  RA 10h 08m Dec  +22^o

Having commanded - literally! - the lion’s share of attention in the past eleven years or so, the Leonids are now be declining from the high - sometimes exceptionally so - activity which followed the parent comet 55P/Tempel-Tuttle’s early 1998 perihelion passage. No further storm activity is anticipated in the current round, and the Leonid ‘background’ will probably revert to its normal peak ZHR of about 15 in the next few years. This, it should be stressed, is still a respectable showing by any standards, and serious meteor  observers, in for the long haul and not just the ‘glory’ nights, will continue to cover the shower in the years ahead. The regular maximum should occur around Nov 17d 23h UT in 2006.

   Added interest is given to the shower in 2006 by the forecast by McNaught and Asher that we may enjoy one last outburst of enhanced activity – to perhaps double ‘normal’ Perseid levels – around Nov 19d 04h 45m UT. This makes the Saturday-Sunday of Nov 18-19 a potentially very interesting night for meteor observers, and all are encouraged to be on watch in the post-midnight hours (the radiant doesn’t rise until after 22h local time) on this night. While there is no guarantee of high activity, observations positive or negative will be very important in testing the – so far – successful model of the Leonid meteor stream as a collection of separate ‘filaments’.  

Local Time (53^oN)   Radiant Altitude     Local Time    Radiant Altitude

23h                                  14.8^o                          03h                    41.7^o

00h                                  15.0^o                          04h                    49.6^o

01h                                  23.9^o                         05h                    55.8^o

02h                                 32.9^o                          06h                    58.9^o 

With New Moon promising dark skies, at least, and the radiant high in the eastern sky at the time of the possible outburst peak, the Leonids in 2006 could hardly be better placed. Even if no exceptional activity is seen, the shower’s usual performance sees a healthy smattering of fast (entry velocity 70 km/s) meteors, including several bright events with lingering persistent ionisation trains. 
 

Geminids

Active December 7-16

Radiant RA 07h32m Dec +33^o

BAA observers have obtained many useful data on this shower over the past 25 years, charting an increase in intensity and broadening of the maximum, which occurs around December 13-14. Having had a fairly narrow peak in the 1960s, the Geminids currently show activity in excess of that found during a typical Perseid maximum over a 36-hour interval it is usually the case that watches on Dec 12-13 and/or 14-15 can be almost as productive, in terms of meteor numbers, as those on maximum night. Corrected peak Geminid Zenithal Hourly Rate in recent years has been of the order of 100-120, corresponding to observed rates up to 80 meteors/hr and more. Commonly, the meteors come in ‘clumps’, and it is not uncommon for spurts of four or five Geminids to be reported in a minute, following which there may be a brief lull in activity.

     The Geminid radiant lies just north of Castor, and is above the horizon throughout the hours of darkness in the British Isles in mid-December, reaching its highest elevation around 01h local time; productive watches are possible from mid-evening onwards. 

Local Time (53^oN)   Radiant Altitude     Local Time    Radiant Altitude

20h                                    25.4^o                     00h                    60.5^o

21h                                    34.1^o                     01h                    67.1^o

22h                                    43.1^o                     02h                    70.0^o

23h                                    52.1^o                     03h                    67.4^o 

Geminid meteors are produced by debris from asteroid (3200) Phaethon. The meteoroids have a rather different - rocky, as opposed to dusty - nature from those in cometary streams such as the Perseids or Leonids, meaning that they are mechanically more robust and last longer in luminous flight, penetrating the atmosphere to somewhat lower altitudes. Their relatively slow entry velocity (35 km/s) and reasonably abundance of bright events make the Geminids a good photographic target.

      The early parts of the 2006 return are rather affected by moonlight; Full Moon falls on December 5. Maximum activity is expected to around Dec 14d 05h UT. For observers in the British Isles, best visual rates can probably be expected in early evening before the last quarter Moon rises on the Wednesday-Thursday of December 13-14. Moonrise occurs around 01h local time on this night, at which time the radiant will have attained an elevation of just over 60 degrees in UK skies.

       A well-documented feature of the shower is the increased proportion of bright Geminids in the interval after the very highest visual rates. It is possible that although numbers will be gradually declining as time goes by on Dec 14-15, observers will find the activity laced with occasional slow, very bright and spectacular Geminids.