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Re: Refraction and humidity
From: Richard B. Langley
Date: 2007 Mar 28, 10:40 -0300
From: Richard B. Langley
Date: 2007 Mar 28, 10:40 -0300
Very thorough discussion on refraction: "Understanding Astronomical
Refraction" by Andrew T. Young in The Observatory, Vol. 126, No. 1191,
April 2006, pp. 82-115.
-- Richard Langley
On Wed, 28 Mar 2007, Alexandre E Eremenko wrote:
>
>
>Bill,
>The most advanced text on astronomical refraction
>I have is the chapter of Chauvenet where he explains
>the work of Bessel, and attaches tables computed by Bessel's
>formula with refraction in fractions of a SECOND.
>Bessel's formula does not take into account color or
>humidity. Chauvenet says that Bessel's tables give
>satisfactory results, and he does not mean observations
>with a sextant to a fraction of a minute, but
>he means real astronomical observations with instruments
>of high precision.
>
>That's why I assume that color and humidity can be safely neglected
>in the type of observations we do, as well as temperature and
>pressure in most cases.
>
>Alex
>
>On Tue, 27 Mar 2007, Bill wrote:
>
>>
>>
>> Alex
>>
>> Following up on Sunday's conversation on refraction for star-to-star angular
>> separation, the almanac states mean refraction is calculated for a
>> temperature of 10C, pressure of 1010 mb, humidity of 80% and wavelength of
>> 0.50169um.
>>
>> That would indicate my recollection that humidity is a component of
>> refraction is correct, and my belief that the color of a star/body may
>> affect refraction. I do not know if dust in the air will affect refraction
>> like humidity.
>>
>> The important point in context is how much refraction will be affected,
>> especially for lower bodies (20d to 30d). I don't have a clue. Perhaps the
>> list can be of help.
>>
>> Bill
>>
>>
>>
>>
>>
>> >
>
>
>>
>
===============================================================================
Richard B. Langley E-mail: lang@unb.ca
Geodetic Research Laboratory Web: http://www.unb.ca/GGE/
Dept. of Geodesy and Geomatics Engineering Phone: +1 506 453-5142
University of New Brunswick Fax: +1 506 453-4943
Fredericton, N.B., Canada E3B 5A3
Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/
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