Starship Asterisk*

The reason why an 18,000 K blackbody is generally considered the most blue (and why most people see it that way) is that this is the temperature where you have the most "blue" (450 nm) energy in comparison with longer visual wavelengths. As you get hotter, the energy across the visual spectrum gets flatter, with relatively more energy at longer wavelengths compared to blue (you always have more in total at the short end, it's just that the distribution gets flatter).

Chris Peterson wrote:

Ann wrote:

Why do stars look their bluest at 18,000 K? And if so, why did 35,000 K Lambda Orionis look so strikingly blue to me?

I can't say why things do or do not look certain colors to you. While it's possible your eyes are physiologically different from those of most people, I suspect it's simply how your brain processes color. Certainly, color perception is far more complex than just the chemistry of the retina would suggest. Different people certainly see color differently. I'll say that I've never seen a star that I'd call strikingly blue. In fact, I'd describe stars that are classified as blue as visually being cold white.

The reason why an 18,000 K blackbody is generally considered the most blue (and why most people see it that way) is that this is the temperature where you have the most "blue" (450 nm) energy in comparison with longer visual wavelengths. As you get hotter, the energy across the visual spectrum gets flatter, with relatively more energy at longer wavelengths compared to blue (you always have more in total at the short end, it's just that the distribution gets flatter).

johnemac wrote:since the final phase of the planetary nebula phenomenon for the star itself
is collapse to the white dwarf stage (immediately following the generation of
the planetary nebula), how can the white dwarf be 10 billion years old, and
the nebula be only 20 thousand ?? am i missing something ?

geckzilla wrote:Starsurfer: Of course it shows it to be blue. After you do the color balancing, things which are more strongly emitting shorter wavelengths have nowhere else to go. And colors presented are most certainly influenced by saturation and sharpening, especially when a star is in the middle of a faint planetary nebula that someone is paying special attention to and possibly giving it selective treatment over the rest of the stars in the image. Anyway, I'm not saying that they aren't bluer, just that things are not necessarily blue. The stars in the middle of planetaries are definitely special stars.

starsurfer wrote:

geckzilla wrote:Starsurfer: Of course it shows it to be blue. After you do the color balancing, things which are more strongly emitting shorter wavelengths have nowhere else to go. And colors presented are most certainly influenced by saturation and sharpening, especially when a star is in the middle of a faint planetary nebula that someone is paying special attention to and possibly giving it selective treatment over the rest of the stars in the image. Anyway, I'm not saying that they aren't bluer, just that things are not necessarily blue. The stars in the middle of planetaries are definitely special stars.

For the star to appear blue after saturation, it must have been blue in the raw unprocessed data in the first place.

starsurfer wrote:For the star to appear blue after saturation, it must have been blue in the raw unprocessed data in the first place.

geckzilla wrote:

starsurfer wrote:

geckzilla wrote:Starsurfer: Of course it shows it to be blue. After you do the color balancing, things which are more strongly emitting shorter wavelengths have nowhere else to go. And colors presented are most certainly influenced by saturation and sharpening, especially when a star is in the middle of a faint planetary nebula that someone is paying special attention to and possibly giving it selective treatment over the rest of the stars in the image. Anyway, I'm not saying that they aren't bluer, just that things are not necessarily blue. The stars in the middle of planetaries are definitely special stars.

For the star to appear blue after saturation, it must have been blue in the raw unprocessed data in the first place.

Incorrect. Raw => Color balance => Saturation increase
The color balance is where the blue is coming from.

Starsurfer wrote:
When Don Goldman processes his images, the colour balance for the stars is based on a G2V star.

starsurfer wrote:When Don Goldman processes his images, the colour balance for the stars is based on a G2V star.

Chris Peterson wrote: The reason why an 18,000 K blackbody is generally considered the most blue (and why most people see it that way) is that this is the temperature where you have the most "blue" (450 nm) energy in comparison with longer visual wavelengths. As you get hotter, the energy across the visual spectrum gets flatter, with relatively more energy at longer wavelengths compared to blue (you always have more in total at the short end, it's just that the distribution gets flatter).

Chris Peterson wrote:

Boomer12k wrote:Not even a good comparison...my thinking....not the same type of object....Tarantula is not a Planetary Nebula....though further away by far...is more massive, contains more stars, is a total region in itself, etc....should really be compared to a Planetary Nebula of the same distance....

I think the comparison was meant to be of interest to imagers, who have some idea about the brightness of the Tarantula. The comparison was purely one of how many photons are received at the camera, nothing to do with the intrinsic brightness of the objects. So the types of objects aren't really important, only that they are extended and of similar scale.