Nitpicker wrote: Ann wrote:
The appearance of galaxy NGC 3319 is most interesting. It appears to have a blue bar and three bright blue knots of intense star formation. This SDSS g-r-i image
suggests that the star formation in the bar is real, and two of the three blue knots in an arm really seem to be pockets of star formation. The third blue knot appears to be a foreground star, however, and not even a blue one.
And there's a comet in front, too. And little lambs eat ivy.
It is a great image. But it is perhaps a little silly to be comparing colours with another image, when the filter/exposure/processing details of neither are readily available.
I certainly realize that Alessandro Falesiedi didn't produce his very fine photo primarily in order to bring out the true colors of NGC 3319. Obviously this is a comet portrait more than anything else, or rather, it is a portrait of a comet seen against the sky.
There is absolutely no reason for Alessandro Falesiedi to make sure that his NGC 3319 colors are correct, but I wanted to check them against other pictures of NGC 3319. Again, not all galaxy pictures do a good job of bringing out the colors of the galaxy, but I generally trust SDSS. They use the same filters and often, though not always, the same processing and color balance. That is why I feel confident, judging from the SDSS picture, that the bar of NGC 3319 really is quite blue and really contains quite a lot of star formation. There are also two bright pockets of star formation in an arm, but a similarly bright point of light close to them is yellow in color and therefore not something that belongs to the galaxy. It is too bright to be a red giant in NGC 3319, so it is almost certainly a foreground star.
Compare the SDSS picture with this image
by Adam Block. It shows a blue bar, two intense purple knots of star formation, and a yellow-orange stellar object that is most likely a foreground star.
By the way, the yellow star close to the comet in today's APOD is almost certainly HD 92388, a modest eighth magnitude K0 star.
Anyway, the main reason why I brought up the blue bar in NGC 3319 is that blue galactic bars are unusual. Galactic bars are generally old, stable features, made up of old yellow stars. The fact that the bar of NGC 3319 is bursting with young blue stars makes this galaxy unusual.