(meteorobs) meteorobs Digest, Vol 5, Issue 19

[Saunders Stuart]

  Dear Marco,
	Thank you for your reply - I think I understand it.

	It appears then that it the increase in fireballs is a matter of  
degree, or is it more significant? Also, does the lack of meteor  
showers make the fireballs more conspicuous?

	Best regards,
	Stuart.


> Op 24-2-2010 09:42, Stuart Saunders schreef:
>> Robert, you say "February is the start of the fireball season, when  
>> an
>> abundance of fireballs seem to occur. This lasts well into April and
>> seems to occur mostly during the early evening hours."
>>
>> I am wondering are these from one or a few radiants, or are they
>> random? What might cause random fireballs in a particular season, and
>> in the evening - contrary to earths motion, etc?
>>
>> I would be grateful for any thoughts.
>>
>> Stuart.
>
> During this period, the highest part (in declination) of the  
> ecliptic, in the northern hemisphere, is high in the sky in the late  
> afternoon and early evening.
>
> This means that activity from ecliptic sources (sporadic asteroidal  
> origin meteoroids) are favoured as their source area is relatively  
> high in the sky.
> These are objects in prograde orbits with similar speeds to the  
> earth - their radiants will tend to cluster near the opposit side of  
> where the earth is moving to. This point is higher in the sky in  
> northern hemisphere spring evening. By contrast, retrograde,  
> sporadic cometary origin meteoroids will tend to have their radiant  
> clustered near the point where the earth is moving to. Their  
> activity will be highest in northern hemisphere autumn mornings.
>
> Asteroidal meteoroids tend to be relatively big and solid relative  
> to cometary meteoroids (they are the potential meteorite producers).  
> Hence their fireball potential. In spring, the asteroidal sporadic  
> source is hence more active (favourable radiant area position in the  
> evening sky) and they are relatively large. Together, this means:  
> good fireball activity. But don't let this fool you. You need to  
> observe a lot of spring hours to capture them.
>
> - Marco
>
> -----
> Dr Marco (asteroid 183294) Langbroek
>