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(meteorobs) Measuring Meteor Brightness (an observing fundamental)


A recent subscriber to 'meteorobs' sent me an excellent question: they saw me 
using the N.A.M.N. Velocity Scale (0 to 5) for meteor SPEEDS, but wondered how 
I was measuring the BRIGHTNESS of the meteors I saw? So, I thought I'd scribble 
something up in response: you can find out more about this and other observing 
techniques by getting ahold of one of the "observing handbooks" out there: 
NAMN's is great for beginners; the IMO Handbook is a vital reference; and the 
new Handbook due out by American Meteor Society should be excellent!


The brightness scale used throughout astronomy is the "Magnitude Scale". This 
is a reverse logarithmic scale: the HIGHER a magnitude number, the FAINTER the 
object; "logarithmic" means that first magnitude is actually about 2.5 times 
brighter than magnitude 2, which is 2.5 times brighter than mag 3, etc. The 
brightest true star in the sky is "Sirius", at magnitude -1.5. The full moon is 
magnitude -12! The faintest stars you can glimpse with your eyes on a moonless 
night in the deep woods are probably either magnitude 6 or 7.

The way we assign a magnitude to every METEOR we see is just by comparing it to 
nearby stars! For instance, if I see a meteor overhead early tomorrow morning, 
I'll compare it with the stars I saw it near: if it seems fainter to me than 
yellow Capella (also known as Alpha Aurigae), and yet brighter than nearby 
Menkalinan (Beta Aurigae - the star next to Capella), I know it's between 
magnitude 0 (Capella) and 2 (Menkalinan), and so I log it as "mag 1"...

This technique takes just a little practice, but quickly becomes second nature. 
The tough part is learning enough comparison stars for all the different areas 
of the sky, and all the different magnitudes! I do this by "cheating": before I 
start an observing session, I'll check my IMO Limiting Magnitude charts. These 
charts also have star magnitudes for a variety of stars marked on them: I look 
for a sampling near my field of view, and memorize their magnitudes.

Note that this "comparison star" technique is pretty the same one that people 
use when logging observations at the telescope: whether their observing the 
moons of Jupiter, a variable star, the stars in an open cluster, etc.


By the way, questions like the above are VERY welcome on meteorobs: if you've 
been "lurking" for a while and have some "meteor fundamentals" you're wondering 
about, be sure to post them! There are probably a lot of other folks who are 
wondering the same thing, or WOULD be if they thought about it. :)

Clear skies,
Lew