Re: [ATM] Dark Sky Meter

["Jim Miller" <jim@jtmiller.com>]

hi donald

any suggestions for a standard source?

digital readout would be possible but at additional cost and complexity. 
since the code for the micro would be published anyone could add it as an 
option. the ability to connect this to a external computer would seem to 
satisfy those who want additional complexity of gps etc.

i've read the ida stuff and while interesting seems to be focused on 
relative readings only and subject to observer training. i'm trying (perhaps 
foolishly) to get an absolute measurement device.

jtm
----- Original Message ----- 
From: "Donald Good" <donald.good@comcast.net>
To: "'Jim Miller'" <jim@jtmiller.com>; "'ATM'" <atm@atmlist.net>
Sent: Sunday, September 26, 2004 4:53 AM
Subject: RE: [ATM] Dark Sky Meter


A few thoughts:

> -----Original Message-----
...
> approach
> - silicon photodiode with lens to give 4°FOV (matches telrad)
> and suitable collection area
> - charge integrating preamp and comparator under
> microprocessor (PIC) control
> - beeper (morse code?) readout with optional phone jack to
> connect to computer
> - aim device and press start button to capture data, device
> beeps result when done

A digital readout (LCD or LED) would be more convenient and reliable than
trying to listen, interpret, and record a beep code.  An A2D converter IC
and a digital display IC would help.
>
...
>
> calibration target would be vega at zenith on a "clear" night.

If an absolute reading is desired, you can't calibrate on a variable target.
How do you judge a clear night?  What about sky glow background around Vega
during the calibration?  Also, Vega will not reach zenith in all locations
or in all seasons.

A standard source must be used for calibration.  A few might be acquired and
traded around as needed for calibration.

A standard procedure would be needed.  Date, time (Standard time? e.g. 10PM
or midnight [true, not daylight savings]or multiple times?), location,
weather (cloud) conditions, readings (zenith and 4, 6, or 8 equi-angular
directions at specific altitude angle, e.g. 30 or 45 deg).  Directions might
be relative to north or the brightest part of the sky, e.g. toward a city
glow.  As such, a GPS (or a way to obtain GPS coordinates for a location)
and a compass would be needed to take readings.

Does the International Dark-Sky Association have a procedure in place?  If
so, why try to re-invent the wheel?

Clear (dark) skies.
Don

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