Many magnitude estimates may have been made from plates taken specifically in blue light, such as those of the earlier Polomar survey. (Just a guess...)

-----Original Message-----
From: James Cobb [mailto:james@cobb.name]
Sent: Wednesday, December 17, 2003 5:37 PM
To: Utah Astronomy
Subject: Re: [Utah-astronomy] In the blue

I believe he is referring to magnitudes obtained from black and white photography; it is biased toward blue light.

Jim

----

Jim Cobb

james@cobb.name

On Dec 17, 2003, at 5:12 PM, Gibson, Jim wrote:

I was just reading an article about the Herschel 400. The author Jay Reynolds Freeman made this statement:

I have informally known for a long time that many older cataloged magnitudes of deep-sky objects systematically underestimate their brightness to the visual observer--the fact that many magnitudes were obtained in blue wavelengths guarantees that result...

What does it mean "obtained in blue wavelengths "? How are magnitudes obtained in the blue wavelengths?

Jim

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