by Chris Peterson » Sat Sep 10, 2022 2:36 pm
Ann wrote: ↑Sat Sep 10, 2022 4:49 am
So Vega may look white in the APOD, but look at its reflection in the lake. Is it blue
███ or is it blue
███ ? Just saying!
Bright stars saturate camera sensors. That is, they fill the red, green, and blue pixels to their maximum value. And what color do you get when red, green, and blue all have the same high value? White. So bright stars usually look white in images. How do we see them in something approximating their true colors? We can defocus the lens a bit (or our eyes, through a telescope). We can let them trail, so the exposure on any one pixel is shorter. We can image at a high enough magnification that stars show obvious halos, which don't saturate. Or we can see them reflected, especially in moving water, which spreads their light out over a lot more pixels. And indeed, we've seen all of these techniques (deliberate or accidental) used in APODs over the years.
[quote=Ann post_id=325732 time=1662785350 user_id=129702]
So Vega may look white in the APOD, but look at its reflection in the lake. Is it blue [color=#A6EDFF]███[/color] or is it blue [color=#A6EDFF]███[/color] ? Just saying!
[/quote]
Bright stars saturate camera sensors. That is, they fill the red, green, and blue pixels to their maximum value. And what color do you get when red, green, and blue all have the same high value? White. So bright stars usually look white in images. How do we see them in something approximating their true colors? We can defocus the lens a bit (or our eyes, through a telescope). We can let them trail, so the exposure on any one pixel is shorter. We can image at a high enough magnification that stars show obvious halos, which don't saturate. Or we can see them reflected, especially in moving water, which spreads their light out over a lot more pixels. And indeed, we've seen all of these techniques (deliberate or accidental) used in APODs over the years.