Starship Asterisk*

Ann wrote:
I should add that one reason why the stars so rarely collide is that they are zipping by one another really fast.

• Example:
  
  Alpha Centauri has a proper motion across the sky of ~23.3 km/s.
  
  The minimum angular velocity necessary to avoid colliding with the sun from that distance is just ~2 mm/sec.

https://en.wikipedia.org/wiki/Stellar_collision wrote:
<<While stellar collisions may occur very frequently in certain parts of the galaxy, the likelihood of a collision involving the Sun is very small. A probability calculation predicts the rate of stellar collisions involving the Sun is 1 in 10²⁸ years. For comparison, the age of the universe is of the order 10¹⁰ years.

Even though our star will likely not be directly affected by such an event, the Earth may, however, be easily affected by a nearby collision. Astronomers say that if a stellar collision happens within 100 light years of the Earth, it could possibly result in Earth's destruction. This is still very unlikely though because there are no stellar clusters this close to the Solar System.>>

https://en.wikipedia.org/wiki/Blue_straggler#Formation wrote:

Several explanations have been put forth to explain the existence of blue stragglers. The simplest is that blue stragglers formed later than the rest of the stars in the cluster, but evidence for this is limited.[5] Another simple proposal is that blue stragglers are either field stars which are not actually members of the clusters to which they seem to belong, or are field stars which were captured by the cluster. This too seems unlikely, as blue stragglers often reside at the very center of the clusters to which they belong. Another theory is that blue stragglers are the result of stars that come too close to another star or similar mass object and collide.

Ann wrote:

Oldironsides wrote:Forgive me for the intrusion but I am more of a visitor than a commentor to APOD. I think I have raised the question once before but this image and the discussion about the diffraction spikes has refreshed my memory. The image explanation says it spans a distance of 17 light years but there seems to be an awful lot of stars in this cluster and while the diffraction spikes only add to the clutter I am wondering how far apart these stars are to one another? While the span, left to right may be only 17 light years, the photographic compression (foreground to background) could still be much more than that. But still these stars seem close enough to fit inside our Solar System. Any guess how far apart they are?

According to the caption, the entire image spans about 17 light-years, but the central concentration of stars is much smaller. Could the densest part of the central core be, perhaps, 3 light-years?

To estimate how close the stars are to one another, we need to know how many stars reside in a given volume. I have been unable to find an estimate of the number of stars in NGC 3603. If we include low-mass stars, however, I would think we must be talking about several thousand stars, quite possibly more than 10,000 stars for the entire cluster, and almost certainly no less than a thousand stars for the central compact core.

Would these stars fit inside our own solar system? Well, bearing in mind that the outer part of the solar system, the Oort Cloud, is supposed to extend a light-year or so from the Sun, then absolutely, there would have to be many stars in NGC 3603 within the volume of the Oort Cloud. How about the Kuiper Belt? Pluto is supposedly the largest of the Kuiper Belt objects, and its average distance to the Sun is 39.5 AU, or 39.5 times the distance from the Sun to the Earth. Yes, I think there might well be several stars within a radius of 39.5 AU in a cluster like NGC 3603, and that might include stars that are not binary or multiple stars per se, but just stars that are zipping past one another at high speeds.

Ann

Oldironsides wrote:Forgive me for the intrusion but I am more of a visitor than a commentor to APOD. I think I have raised the question once before but this image and the discussion about the diffraction spikes has refreshed my memory. The image explanation says it spans a distance of 17 light years but there seems to be an awful lot of stars in this cluster and while the diffraction spikes only add to the clutter I am wondering how far apart these stars are to one another? While the span, left to right may be only 17 light years, the photographic compression (foreground to background) could still be much more than that. But still these stars seem close enough to fit inside our Solar System. Any guess how far apart they are?

starsurfer wrote:

geckzilla wrote:

starsurfer wrote: Just want to ask, do you appreciate raw data?

Usually. Some more than others. Some of it is so rife with defects that it hurts my eyes. Sometimes it's just breathtaking on its own; I always felt this way when I looked over one of the freshly pipelined Frontier Fields. Whether or not it's still considered "raw" after it's been through the pipeline is up to one's discretion. It's raw enough to be called raw to me in some regards.

Some Hubble and ESO data is absolutely brilliant, especially some planetary nebulae! I think the brain and eyes perceive monochromatic images differently to colour?

geckzilla wrote:

starsurfer wrote:

geckzilla wrote: Absolutely. But it doesn't produce a truer representation of the sky. It does nothing but change the aesthetics of the image. There is also no single agreed upon "truth" in sky representation. The raw data is as objective and untouched as it can be, but not a whole lot of people appreciate raw data.

Just want to ask, do you appreciate raw data?

Usually. Some more than others. Some of it is so rife with defects that it hurts my eyes. Sometimes it's just breathtaking on its own; I always felt this way when I looked over one of the freshly pipelined Frontier Fields. Whether or not it's still considered "raw" after it's been through the pipeline is up to one's discretion. It's raw enough to be called raw to me in some regards.

starsurfer wrote:

geckzilla wrote:

heehaw wrote:So has anyone ever tried editing an astronomical photograph to remove the telescope-mirror support effects, and produce a truer representation of the sky?

Absolutely. But it doesn't produce a truer representation of the sky. It does nothing but change the aesthetics of the image. There is also no single agreed upon "truth" in sky representation. The raw data is as objective and untouched as it can be, but not a whole lot of people appreciate raw data.

Just want to ask, do you appreciate raw data?

geckzilla wrote:

heehaw wrote:So has anyone ever tried editing an astronomical photograph to remove the telescope-mirror support effects, and produce a truer representation of the sky?

Absolutely. But it doesn't produce a truer representation of the sky. It does nothing but change the aesthetics of the image. There is also no single agreed upon "truth" in sky representation. The raw data is as objective and untouched as it can be, but not a whole lot of people appreciate raw data.

Ann wrote:But in today's APOD the diffraction spikes mostly clutter up the image and make the star images overlap, so that the resolution of individual stars becomes more difficult.

Chris Peterson wrote:

rstevenson wrote:Here's the ESO page I was referring to. It seems categorical on the issue.

Seems like they're talking about producing aesthetic images for outreach, not scientific processing. That's a whole different thing.

rstevenson wrote:Here's the ESO page I was referring to. It seems categorical on the issue.

rstevenson wrote:I found a page on the ESO site with advice about working with raw image files, in which they say...

Diffraction pattern: the "spider", that is the arms that support the secondary mirror of the telescope, causes a diffraction pattern that usually appears as a cross around the brightest stars. This pattern is part of the image, and must not be cleaned out. ... The diffraction patterns are part of the image, they should not be removed.

Looks like the astro imaging crowd has decided the issue once and for all, and we deviants should tug our forelocks and go away.

geckzilla wrote:

heehaw wrote:So has anyone ever tried editing an astronomical photograph to remove the telescope-mirror support effects, and produce a truer representation of the sky?

Absolutely. But it doesn't produce a truer representation of the sky. It does nothing but change the aesthetics of the image. There is also no single agreed upon "truth" in sky representation. The raw data is as objective and untouched as it can be, but not a whole lot of people appreciate raw data.

rstevenson wrote:

heehaw wrote:... So has anyone ever tried editing an astronomical photograph to remove the telescope-mirror support effects, and produce a truer representation of the sky?

A few years back I emailed the author of my favourite image editing software -- GraphicConverter -- to ask if there was any chance of a filter being created to remove spikes from astro images. He replied, "Sorry, I have currently no idea for a good filter." And that was that. I can see the problem easily enough: the spikes are not easily selectable -- believe me, I've tried. So, we unspike-able individuals will just have to accept that some images have spikes. For now.

heehaw wrote:... So has anyone ever tried editing an astronomical photograph to remove the telescope-mirror support effects, and produce a truer representation of the sky?

Diffraction pattern: the "spider", that is the arms that support the secondary mirror of the telescope, causes a diffraction pattern that usually appears as a cross around the brightest stars. This pattern is part of the image, and must not be cleaned out. ... The diffraction patterns are part of the image, they should not be removed.

heehaw wrote:So has anyone ever tried editing an astronomical photograph to remove the telescope-mirror support effects, and produce a truer representation of the sky?