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Help ! - computing a Balmer line



 
 
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  #1  
Old January 18th 05, 12:28 PM
Maurice Gavin
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Default Help ! - computing a Balmer line

I've posted a simple OG spectrum of Comet Machholz and Algol at

http://home.freeuk.com/m.gavin/digsky.htm

where the star records on the Canon CMOS sensor to the Balmer line
H-lambda [line 11 where H-alpha = line 1 at 656.3nm] in near UV.

Can someone compute the wavelength of H-lambda please?
I've got the formula but don't think H-alpha = 1 and in any case my
calculator's dead!
  #2  
Old January 18th 05, 03:06 PM
William C. Keel
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Maurice Gavin wrote:
I've posted a simple OG spectrum of Comet Machholz and Algol at


http://home.freeuk.com/m.gavin/digsky.htm


where the star records on the Canon CMOS sensor to the Balmer line
H-lambda [line 11 where H-alpha = line 1 at 656.3nm] in near UV.


Can someone compute the wavelength of H-lambda please?
I've got the formula but don't think H-alpha = 1 and in any case my
calculator's dead!


I have the following list, the higher members of which I believe
to have been computed on a day when my brain was fully engaged:

Balmer
6562.80 H-alpha
4861.32 H-beta
4340.46 H-gamma
4101.73 H-delta
3970.07 H-epsilon
3889.05 H8
3835.38 H9
3797.90 H10
3770.63 H11
3750.15 H12
3734.37 H13
3721.94 H14
3711.97 H15
3646.0 Balmer limit

(the numbering there is in the system in which it denotes the number
n of the upper level for the transition, so your 11 is my 13...)
In Angstroms, the formula would be
wavelength = 911.75 / (1/n^2 - 1/m^2)
where m and n are the principal quantum numbers of the two levels
involved (for H-alpha, m=3,n=2; for H-beta, m=4...) and 911.75 is the
vacuum wavelength of the Lyman limit (13.6 eV). The only missing
piece is that these are vacuum wavelengths, needing modification for the
index of refraction of air (multiply by 1/index). The table gives
air wavelengths (I tnik that was for standard temperature and pressure).

Bill Keel
 




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