Hi everybody,
We are always striving for best color rendition in astrophotography. With the Photometric Color Calibration, we have got a new, very useful tool to select the white point. For stars, most people would consider a G2V star as white reference, there have been many papers published in the past claiming that. However, is this really true? Is the sun a white star or a yellowish star? And what is the role of our atmosphere? When we look at historic publications of the last centuries, many observers described the colors of stars. They mostly found that A and F type stars are bluish white to yellowish white, G type stars are yellow and the like. A very popular book written by the famous David Malin and co-author Paul Murdin, "Colours of the Stars" (1984) is dedicated to this and other topics related to color, and furthermore contains a lot of references.
It is well known that human perception adapts to the color of light, therefore, a sunlit piece of paper always looks white to us, independently on the daytime and cloud conditions, meaning color temperature. On the other hand, when I observe Capella (spectral classes G8/G0, binary system), it clearly shows a yellow tint to me.
So what is the correct white reference point spectral class for stars? Really G2V, or perhaps A5, or F0? It would be very interesting to hear your opinions.
Juergen
