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Re: (meteorobs) Re: NM past South Delta Aquarid rates

Kim,

Although some observers have more years of observing experience than 
I do, I have had good success with late July nights for the past few 
years. Late July is usually consistently clear for me, and makes it 
easier to view the SDA activity as well as all the minor showers in 
the south. Because I am at 45 degrees latitude, the SDA radiant never 
rises quite high in the sky. Rates can be decent but not really 
spectacular. With a brightening moon in the sky, the many faint 
members of SDA will be unseen. I have seen only a few brighter SDA's, 
but no fireball from them yet. Norman's data was interesting. When 
time allows, I'll see if I can post some data in a similar way for 
years 1995 to 1998.

I feel it's a good idea not to get overwhelmed with too many 
radiants. It's much better, as you say, to be careful with shower 
association. This way, your data is much more reliable. With time, 
the more minor showers can be monitored, but it requires far more 
care as accidental sporadic alignment can happen easily.

It seems to me that the SDA's produce fairly dependable rates every 
year when the moon is abscent. The SDA's should be a relatively old 
diffuse shower, which is why its activity period is spread over so 
many days. With time, I feel this shower will follow a trend of 
gradual decreasing rates, and the peak will become even more broader 
and less obvious.

For velocities, it often happens for me to call different but not 
always close velocities for a shower. It all depends mainly on the 
distance of the meteor from the radiant. Sometimes it involves 
whether the meteors are seen in the early evening or before dawn. 
Evening meteors can appear to move slower, as they have to catch up 
more with earth. With the swift Perseids (59 km/sec), I usually call 
most meteors as a 5 or a 4. Short Perseids close to the radiant can 
appear as 3 or even 2 if they are seen coming right out on an almost 
head-on path. If I'd ever see a Perseid *directly* on the radiant as 
a tiny star like flash, I would call it a *0* (stationary)! So, it 
all depends mainly on perspective.

I agree that very short meteors are difficult to assign correctly, 
especially the faint ones. Unless I face the radiant, most head-on 
meteors occur on the edge of my field of view. When no trains are 
produced, I'm sometimes left wondering if I really saw something. For 
the Perseids, I always like to face a little further from the radiant 
to catch many of the longer paths meteors, which the eye sees more 
easily anyway. For me, an optimum field of view is about 30 degrees 
away from the radiant, and at least more than half way up to the 
zenith from the horizon (60-70 degrees high).

By the way, I quite enjoy reading all your reports!
Clear skies for Perseids,

Pierre


Kim Youmans wrote:

>If I saw too few SDA's on the 25/26th this year, that can almost certainly
>be chalked up to my inexperience!  I have caught myself too many times this
>year not paying attention to the possible radiant origins of meteors I spot.
>And I've offered the disclaimer several times that I probably have too many
>sporadics and not enough shower members listed in my reports.  On the other
>hand, I am very careful about the ones I do ascribe as shower 
>members -- I note
>shower velocities and arc length as related to the distance from radiant.
>     Norman's list of past rates is very informative!  It leads me to ask one
>question...do the SDA's have a dependable rate year to year?
>     Not straying too far from the subject, I have a couple of other lingering
>questions about velocities.
>           A.   Is is possible to see different but close velocities from the
>same shower.  For instance, could I designate one leonid as a 5 and another as
>a 4?  Would this difference be subjective or due to perspective?
>           B.  When meteors have extremely short path lengths, I find it quite
>difficult to give many of them what I feel would be accurate velocity ratings.
>Should I take Lew's advice and just "call 'em as I see 'em" (as best I can)?
>                      Thanks up front,             Kim Youmans

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