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