[Prev][Next][Index][Thread]

Re: (meteorobs) Limiting Magnitude


Kim Youmans posted a great reply to Asaf's questions on Limiting Magnitude.
As Kim says, recording frequent LMs is one of the things which distinguishes
a scientific amateur meteor observer from someone "just watching" - without
the LM (and probably at least magnitude estimates for the meteors you see),
people will have great difficulty making any scientific use of what you saw.

Your logs won't necessarily be "USELESS"! But the work needed to render your
observation comparable to those of other observers around the world, and the
inherent errors introduced by this kind of "compensation after the fact",
make it really FAR less likely that you'll make a major contribution...


One gnit to gpick on Kim's reply, where he wrote:

>A good observer will count at least three of these regions, one near zenith,
>one at about 40-60 degrees up, and one near the horizon to get a much better
>idea what his/her total LM really is.  After all, meteors appear in any part
>of the sky, right? ...


Actually, Kim this is exactly what I assumed when I started out - but is not
what the IMO recommends... Reading carefully over the IMO page on LMs at:

    http://www.imodot net/visual/major01.html#sec52

note that they define Limiting Magnitude as "the magnitude of the faintest
star *near the zenith* that the observer can detect using slightly averted
naked eye". And later on, they explicitly state that "The [LM star] fields
should have an elevation of more than 40o".

So in practice, for my own half-hourly LM star counts, I try to use the two
(or three) LM fields which are closest to the Zenith, and that DON'T require
me to move my body or crane my neck at all to count them. That latter item
is key: I've often noted that even craning my neck 30 degrees can really
reduce star counts due to distraction and lack of bloodflow to my eyes (or
brain??), and can even cause what I call "strobing" - where brighter areas
of my peripheral vision seem to "blink" brighter and fainter very rapidly.

[Does anyone else experience this "strobing", especially when fatigued?]

Clear skies and comfortable star counts everybody!
Lew

To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at:
http://www.tiacdot net/users/lewkaren/meteorobs/subscribe.html
Follow-Ups: References: