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Re: (meteorobs) Plotting: Three Stooges Method

Kim,

I understand your "five-thumbs" method of plotting.  While I have not yet
taken up plotting myself, I feel that way often in my other astronomy
endeavours, when I have three charts out, a guide book or two, an extra
eyepiece, and my notebook and pen to record my observations.  I wanted to
share several of my solutions with the list.

To have the space to spread out with all my stuff, I always take along a
card table.  For meteor plotting, a breakfast lap table might work better.
The kind with a pocket along the side(s) to hold stuff.  Meant for the
morning paper, you could use it for extra charts, pencils, other tools.

As a solution for the "flashlight in the mouth" lighting problem, I
modified a swing-arm desk lamp to be a variable-intensity red light.
Basically it's three bright LEDs, and a potentiometer (variable resistor),
connected to a 6V lantern battery.  I ripped the guts out a regular 120V AC
swing arm lamp, mounted the potentiometer where the switch was at the top,
and made a little platform to mount the LEDs where the bulb used to be.  I
put two alligator clips in the place of the plug to make it easy to connect
to the battery.  I can clamp the light anywhere close to where I want to
work, then swivel it so it's always in the right position.  I can adjust
the light to the right intenisity using the potentiometer, including almost
all the way off.

I've also seen people use battery powered head lamps with LED bulb
replacements.  Look for them at outdoor stores, like REI or equivalent.

> ...  I still don't know what one grid on the
>Atlas Bruno chart represents, in degrees, and my Petersons charts have
>the RA and dec, but I can't translate that well into actual degrees.

A degree of dec(lination) is always a true degree.  Can't help with the
Bruno charts.

>     So a few questions:  If I hold my 12" ruler to the sky at arms
>length, how many degrees of sky am I covering?  It is approximately the
>distance from Deneb to Altair.  I know the rule of thumb about fist size
>being 10 degrees and open hand being about twenty, but there can be a
>wide variation there among individuals.

The angular size of your 12" ruler depends on the length of your arm.  The
beauty of the the finger/fist/open hand rules are that people with smaller
hands also tend to have shorter arms, so it all evens out.  A rough way to
learn the angular measure of your ruler is to measure the width of your
open hand, then scale up the angular measure.  For example, my open hand is
about 9 inches, so a 12 inch ruler held at arms length would be 20 deg x
12/9 or 27 degrees.  This only works if the ruler is held at a similar
distance as your open hand, the angle is larger the closer it is held.

For a true measure, the following formula works:

    Let A = the width of the object (in inches or meters)
	    held perpendicular to the line of sight
	B = the distance from the eye to the object (in the same units)

    The angular measure = 2 arctan ( A / ( 2 B ) )

I like Steve's idea for using string to not loose things!  I have found a
local source for triangular pens that don't roll away.

Dark Skies,

Gregg Lobdell
Seattle, WA - 29 days of rain/month, 1 clear day on full moon.


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