(meteorobs) Northern bias to meteor showers?

Fri Feb 2 11:50:47 EST 2007

Actually, there are a lot of biases and plenty of quirks to the current catalogs.  Since there are a lot more observations in the Northern hemisphere, that is a natural bias.  Another one is a very strong bias against radiants that are high in the daytime!  Another bias is that now that we have more precise shower forecasts, most folks only observe on the night of the predicted maximum missing interesting details of the shower.

The newer meteor radars, such as the Canadian CMOR http://aquarid.physics.uwo.ca/cmor.htm have collected literally millions of meteor orbits and are re-defining what it means to be a shower.  The shower radiants can be seen to drift, waxing and waning, over large regions of RA/DEC space often ending up with different names.  The major sporadic sources (anti-helion, torodial, apex, etc) also undergo name changes each month leading to more confusion than illumination.  Meteors are entering a paradigm shift.

Wes

-----Original Message-----
From: meteorobs-bounces at meteorobs.org [mailto:meteorobs-bounces at meteorobs.org] On Behalf Of Bruce McCurdy
Sent: Wednesday, January 31, 2007 5:26 PM
To: Global Meteor Observing Forum
Subject: (meteorobs) Northern bias to meteor showers? 

    Further to my query of last week (copied below for ease of reference), I am trying to do some research on the subject of meteor showers for my next "Orbital Oddities" column in the Journal of the Royal Astronomical Society of Canada. With thanks to Roberto G. for his previous comments, I would very much appreciate some additional expert commentary -- or reference to an authoritative source -- about why meteor showers seem to be heavily biased towards the northern hemisphere. Is it lack of observation by southern observers? A fluke of small number statistics? A temporary/temporal aberration? An asymmetry with respect to the distribution of comet orbits? 
Some other physical cause? Or are my conclusions re: the perceived bias all wet?

    Thanks.

    Bruce
    *****

----- Original Message -----
From: "Bruce McCurdy" <bmccurdy at telusplanet.net>
To: "Global Meteor Observing Forum" <meteorobs at meteorobs.org>
Sent: Tuesday, January 23, 2007 11:15 AM
Subject: Northern bias to meteor showers?

I watched an entire evening match of the Australian Open hoping for a
between-games "skyline" view of Comet McNaught ... which wasn't forthcoming;
what were they thinking? While I waited in vain and watched the tennis, I
spent some of the time pondering the disparity between northern and southern
observing. Many observers have commented that generally speaking one is
better off living in the Southern Hemisphere, what with the centre of the
Milky Way, the Magellanic Clouds, Eta Carinae, the Jewel Box, 47 Tucanae,
more favourable apparitions of Mars and Mercury, and so on. In fact,
somebody recently told me that he couldn't think of a single aspect of
observing in which northerners are better off. I immediately responded that
those in the northern hemisphere have it good when it comes to meteor
observing.

A review of the major showers listed in the RASC Observer's Handbook 2007
reveals how good we have it. Twelve major visual showers (ZHR >= 10) are
listed: Quadrantids (radiant declination +49°), Lyrids (+34°), Eta Aquarids
(-2°), South Delta Aquarids (-16°), Perseids (+58°), Draconids (+54°),
Orionids (+16°), South Taurids (+14°), North Taurids (+22°), Leonids (+22°),
Geminids (+33°), Ursids (+76°). Add them all up and that comes exactly 360°,
an interesting coincidence. More to the point, the *average* radiant is
+30°. I'm not formally trained in statistics but I know enough about them to
realize that this distribution is extraordinary.

The Handbook also lists four daylight showers: Arietids (+26°), Zeta
Perseids (+26°), Beta Taurids (+21°), and D Sextantids (-2°), with an
average radiant of +18°. Not so strong a bias, but still significant.

I then turned to the longer list on the IMO website, wondering if perhaps
the Observer's Handbook (of which I am on the production team) has its own
built-in bias towards northern observers. Only the Puppid/Velid radiant
lists a ZHR as high as 10 and could be considered a borderline "omission"
from the Handbook. 23 of the 32 showers listed by IMO have a northern
radiant, with a raw average of +15°. Since most of the additional southern
radiants were of minor showers I weighted each shower by ZHR (a very rough
exercise, since a few were listed as variable rates which I simply
discounted as ZHR = 0) and again came up with an "average" shower meteor
emanating from +31°.

The IMO list also underscores the imbalance between the two halves of the
calendar year: to arbitrarily choose the most extreme division, between
February-July there are 11 showers, 7 with southern radiants; and from
August-January, there are 21 showers, all but two of them with northerly
radiants. Presumably the imbalance by date is somehow related to the
imbalance by declination, but I wonder whether there might be a physical
explanation for all this.

Since we meteor observers have officially entered the "off-season" it's a
good time to question the many experts who populate this forum. I don't
recall seeing the above subject addressed in the five years I have
subscribed to meteorobs, so I'll ask a simple question: what the heck is
going on?

Bruce
*****

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