Starship Asterisk*

Fred the Cat wrote: ↑Sat Oct 09, 2021 2:40 pm

Chris Peterson wrote: ↑Sat Oct 09, 2021 1:49 pm

Fred the Cat wrote: ↑Sat Oct 09, 2021 1:41 pm The Milky Way galaxy resides in an area of relatively nothing. We investigate physics on Earth but, “Do we live in the best part of the universe to test theories?” Could physics even be tested?

Dark energy theory's themselves could rest in the balance.

There are many, many measurements that we make of things in distant parts of the Universe, all of which offer powerful evidence that the rules of physics we observe here are the same everywhere.

I can only question things from a basic understanding of physics and an interest to know more. When you read lay info, written by physicists, that are questioning topics of the unknown variety, it stirs the curiosity and are fun to share. Like, " If gravitational waves flow along cosmic filaments or through voids or both? Maybe the string section will chime in?

Chris Peterson wrote: ↑Sat Oct 09, 2021 1:49 pm

Fred the Cat wrote: ↑Sat Oct 09, 2021 1:41 pm The Milky Way galaxy resides in an area of relatively nothing. We investigate physics on Earth but, “Do we live in the best part of the universe to test theories?” Could physics even be tested?

Dark energy theory's themselves could rest in the balance.

There are many, many measurements that we make of things in distant parts of the Universe, all of which offer powerful evidence that the rules of physics we observe here are the same everywhere.

Fred the Cat wrote: ↑Sat Oct 09, 2021 1:41 pm The Milky Way galaxy resides in an area of relatively nothing. :| We investigate physics on Earth but, “Do we live in the best part of the universe to test theories?” Could physics even be tested?

Dark energy theory's themselves could rest in the balance. :thumb_up:

Ann wrote: ↑Sun Apr 29, 2018 5:16 am
So the way to understand Gaia's ability to detect M33 and its inability(?) to detect M31 is to realize that Gaia can't photograph a galaxy "all at once", but only "star by star" or "discrete light source by discrete light source". And M31 has too few sufficiently bright discrete light sources in order to show up clearly in Gaia's picture.

https://en.wikipedia.org/wiki/Triangulum_Galaxy wrote:
<<Star formation is taking place at a rate that is strongly correlated with the local gas density, and the rate per unit area is higher than in the neighboring Andromeda Galaxy. (The rate of star formation is about 3.40 Gyr−1 pc−2 in the Triangulum galaxy, compared to 0.74 in Andromeda.)>>

Chris Peterson wrote: ↑Sat Apr 28, 2018 4:56 pm

Ann wrote: ↑Sat Apr 28, 2018 5:07 am Obviously Gaia hasn't been commissioned to measure parallaxes in Andromeda. But would the "Gaia people" intentionally blot out the signal from Andromeda?

I just think that Andromeda is bright enough that it ought to show up in the data. But maybe I'm wrong.

I keep thinking that Gaia's map is showing us M33. Our Local Group smallish spiral would be the grainy object at lower left that forms a triangle with The Pleiades and open cluster M34. In the map, the Pleiades would be the bottom left vertex, M34 would be at top and M33 would be the bottom right vertex.

Again, it isn't simply a question of brightness. It's a question of stellar density, as well. Andromeda has too low a surface brightness, and not many resolvable stars. M33 has a higher surface brightness than M31, and does, indeed, show up in this image. As do several other high surface brightness spiral galaxies in Sculptor, Fornax, and maybe a few more.

Ann wrote: ↑Sat Apr 28, 2018 5:07 am Obviously Gaia hasn't been commissioned to measure parallaxes in Andromeda. But would the "Gaia people" intentionally blot out the signal from Andromeda?

I just think that Andromeda is bright enough that it ought to show up in the data. But maybe I'm wrong.

I keep thinking that Gaia's map is showing us M33. Our Local Group smallish spiral would be the grainy object at lower left that forms a triangle with The Pleiades and open cluster M34. In the map, the Pleiades would be the bottom left vertex, M34 would be at top and M33 would be the bottom right vertex.

BDanielMayfield wrote: ↑Sat Apr 28, 2018 1:00 am Ann, since this is described as a map of the Milky Way, I think only this galaxy and its satellites where included, while other members of our local group where intentionally excluded.

Bruce

bls0326 wrote: ↑Sat Apr 28, 2018 1:18 am The "Not a photograph" link https://apod.nasa.gov/apod/image/milkyway_lund_big.gif is a 1950s drawing version of this photograph. It does show quite a few stars and other astronomical info, including a co-ordinate system. Those folks did a good job also.

Brian

Dale Helms wrote: ↑Fri Apr 27, 2018 3:27 pm I would like to know where we are on this amazing" map", an arrow saying "you are here". I am serious.

Ann wrote: ↑Fri Apr 27, 2018 5:43 pm

Chris Peterson wrote: ↑Fri Apr 27, 2018 1:53 pm

NGC3314 wrote: ↑Fri Apr 27, 2018 12:58 pm I suspect an equally large issue with the all-sky visualization is that stars are not represented as point-spread functions larger than a pixel, so that there is a practical limit to the brightness range shown.

Even the most basic star charting programs will offer stars readily seen with binoculars, so covering perhaps 12 magnitudes, or more than 5 decades of brightness. And these are displayed on monitors with about 2 decades of dynamic range. So the programs cheat by making brighter stars larger, giving them a diameter greater than a single pixel. That fools our eyes and brains a bit, but it doesn't present a terribly realistic image. But it's similar to the artifacts created with images.

I agree that this data is being presented to give the maximum possible spatial detail, which means representing each star as a point. That means compressing many orders of magnitude in brightness down to just a few hundred hue/brightness values. The result is that we don't visually detect any of the individual stellar patterns we're accustomed to.

Thanks, NGC3314 and Chris. The point-source representation of stars and lack of "bleeding pixels" explain why we don't see any bright stars in Gaia's image.

Ann

heehaw wrote: ↑Fri Apr 27, 2018 3:15 pm Hey, fabulous! What most amazes me (though it should not!) are the dust lanes. They are defined so clearly! But of course they are nothing but the ABSENCE of stars in that direction!

Chris Peterson wrote: ↑Fri Apr 27, 2018 1:53 pm

NGC3314 wrote: ↑Fri Apr 27, 2018 12:58 pm I suspect an equally large issue with the all-sky visualization is that stars are not represented as point-spread functions larger than a pixel, so that there is a practical limit to the brightness range shown.

Even the most basic star charting programs will offer stars readily seen with binoculars, so covering perhaps 12 magnitudes, or more than 5 decades of brightness. And these are displayed on monitors with about 2 decades of dynamic range. So the programs cheat by making brighter stars larger, giving them a diameter greater than a single pixel. That fools our eyes and brains a bit, but it doesn't present a terribly realistic image. But it's similar to the artifacts created with images.

I agree that this data is being presented to give the maximum possible spatial detail, which means representing each star as a point. That means compressing many orders of magnitude in brightness down to just a few hundred hue/brightness values. The result is that we don't visually detect any of the individual stellar patterns we're accustomed to.

Chris Peterson wrote: ↑Fri Apr 27, 2018 3:48 pm

Dale Helms wrote: ↑Fri Apr 27, 2018 3:27 pm
I would like to know where we are on this amazing" map", an arrow saying "you are here". I am serious.

We are where your eyes are. This is our view of the sky from the Earth. We're outside the window framed by this image.

Dale Helms wrote: ↑Fri Apr 27, 2018 3:27 pm I would like to know where we are on this amazing" map", an arrow saying "you are here". I am serious.

MarkBour wrote: ↑Fri Apr 27, 2018 4:43 am
That's a fantastic picture. However, Gaia is giving us amazing parallax and hence distance information. What I really want to see is a 3D map of the Milky Way from it. And definitely one I can play with. (Hmmm ... I sound a lot like a spoiled child.)

NGC3314 wrote: ↑Fri Apr 27, 2018 12:58 pm I suspect an equally large issue with the all-sky visualization is that stars are not represented as point-spread functions larger than a pixel, so that there is a practical limit to the brightness range shown.