robin_astro

50 minutes ago, Michael Kieth Adams said:

Baryonic matter, if I got it right, is essentially subatomic particles which are often unassembled atoms

To a cosmologist, Baryonic matter is all normal matter (assembled or unassembled into larger structures like atoms) 

https://astronomy.swin.edu.au/cosmos/b/Baryonic+Matter

We know  how much of that stuff was created at the big bang and it agrees with the latest measurements of all that stuff now. 

Dark matter if it exists was proposed to solve a different problem.  It may be some exotic particle but it has to have different properties from the stuff we already know about and does not interact with it except through gravity

Note that even finding more Baryonic (ordinary) matter would not solve the problem that the postulated (non baryonic) dark matter solves as dark matter would need  different properties to normal (Baryonic) matter to explain the various observations

 https://en.wikipedia.org/wiki/Dark_matter

As you say most of the Baryonic matter in the universe is not in stars but as dust and gas in interstellar space (Not as planets though as they make up a very small fraction of the mass in a typical system).  Various techniques can be used to calculate or measure the total amount of Baryonic matter in the universe  and these appear to be converging on a consensus figure. See "the missing baryon problem" in Wikipedia for example

https://en.wikipedia.org/wiki/Missing_baryon_problem

This is well short of what is required to give the universe its critical density or explain the motion of galaxies though hence leading to the conclusion that there is a much larger fraction of as yet undefined non baryonic (dark) matter

It had been around a long time now but like you, I am still waiting to see any serious results from one. An all reflective design has significant advantages.

The things that put me off is the obvious astigmatism inherent in this type of design which broadens the spectrum which is not good for SNR with faint objects and for looking for structure in extended objects eg comets and galaxies. This is also present to a lesser extent in the Shelyak (Christian Buil's) UVEX reflective grating design where it is tamed by using a cylindrical prism.  I also much prefer the WYSIWYG mirror slit (which both Baader and Shelyak and the old SBig SGS use) over  the beam splitter which is highly dependent on precise alignment and focus between guide camera and slit without being able to see directly what is actually happening at the slit.  If that is out even by a pixel you can lose a lot of light without even being aware of it.  The built in guide camera design could also make the instrument become obsolete, rather like the SGS that used SBig's two chip guider/imager cameras.

Cheers

Robin

I suggest as a starting point something like your 90/f5.6 APO with the 120MM and ~40mm spacing which will give good resolution, plenty of room to fit the spectrum and zero order and plenty of light on bright stars.

With a cooled mono 8300 you will be able to go much deeper. (No need to guide, just stack many shorter exposures) eg these on my BAA page

https://britastro.org/observations/observation.php?id=20230523_183229_5116a1a27f78a1ea

https://britastro.org/observations/observation.php?id=20210406_144443_9e1c6a4cf219d14d

https://britastro.org/observations/observation.php?id=20201216_234948_8cabda965bfe692f

Robin

Hi,

I am the chap who developed the Star Analyser (Almost 20 years ago now !)  You can indeed use almost any camera and telescope but some setups work better than others if you have options. Mono cameras have  many advantages and although the sensor in the 120MM is small it is still  larger than the tiny sensors I originally used with the Star Analyser.  Just use the calculator on the RSpec website (the calculations behind it are mine)

https://www.rspec-astro.com/calculator/

to work out the distance to mount the grating to max out the space you have on the sensor.   The resolution depends on size of the star image relative to the length of the spectrum so a short focal length helps. What model is your 500mm fl refractor?  Well corrected APOs work well but achromats can give problems with chromatism which means the violet end of the spectrum goes out of focus.  The main thing is the SA was developed to get people interested in spectroscopy without spending a fortune  so whatever kit you have, you will get some sort of result and learn about spectroscopy on the way

Cheers

Robin

6 hours ago, vlaiv said:

research claims 5.2 sigma confidence of over density in said region - that is significant if true

6 hours ago, vlaiv said:

 

Once the paper is published watch Fujii trash their statistics as he has done to this team before 😉

9 minutes ago, robin_astro said:

I want to know what makes a shape a shape 🙂

Fujii's paper is critical of the statistical approaches taken and questions whether  these large scale shapes that challenge lambda CDM actually even exist

11 minutes ago, ollypenrice said:

I simply want to know what makes a shape a structure

I want to know what makes a shape a shape 🙂

And in the interest of balance, this paper (and others) dispute these findings

https://academic.oup.com/mnras/article/527/2/1982/7337344

Cheers

Robin

There does not appear to be a paper (even on arXiv) on this particular structure yet so on that basis my view so far  is "there is nothing to see here" 

There is however a paper on the other structure discovered by this team with a paper where their statistical analysis is described, which is of course crucial given the human ability to spot patterns (even where none actually exist!)

https://academic.oup.com/mnras/article/516/2/1557/6657809?

Robin

There are two almost identical looking features side by side in that image 

EDIT: Oops! beaten to it

23 hours ago, dan_adi said:

 result is 4.737e-15 erg/s/cm2/A

This is the flux per unit area surface A of the (theoretical black body) star.  When we measure the flux on earth, the units might look the same,  erg/s/cm2/A but on earth we measure the flux per unit collecting area of the collecting instrument.  The two measurements are not directly related.

See also this similar problem

https://groups.io/g/RSpec-Astronomy/topic/101890725#13418

Cheers

Robin

You are also mixing up absolute and apparent magnitude and if you are trying to relate absolute magnitude to the flux of a black body you have to consider the radius (surface area) of the star

The problem is stars are not black bodies,  the effective temperature Teff is not the temperature of the star and the relationship between B-V and Teff is an empirical not theoretical one

Robin

4 hours ago, johannes1 said:

(the exploitation of periodicity makes me think about pulsars, but since they are point sources I am not clear why you would need imaging capability for those)

Imaging the crab nebula and pulsar through a synchronised shutter was good fun  though

http://www.threehillsobservatory.co.uk/astro/astro_image_33.htm

For Hipparchus read Hipparcos everywhere 😉

On 16/12/2023 at 09:02, StarMen76 said:

I read that Gaia, compared to Hipparchus, increased the number of known parallaxes by 10 thousand times in 20 years. Is there a project that will increase Gaia's results again by 10 thousand times in another 20 years? Around the middle of the century?

Has anyone heard of such a future project? 
I calculated that if to increase the sensitivity of Gaia by 10 thousand times, then its size Gaia must be increased exactly 100 times. T

You have misunderstood where the ability of Gaia to measure a larger number of parallaxes measurable by Gaia comes from. While it is true that Gaia can measure fainter objects, the main advantage of Gaia over Hipparchus is due to its ability to measure parallax to greater precision hence also extending the rage to smaller parallaxes (greater distances). This is mostly due to technological advances, not the increase in aperture (For example Gaia uses wide field CCD cameras allowing direct measurements of angles between objects whereas Hipparchus had to measure each object independently)

Cheers

Robin

On 16/12/2023 at 10:14, StarMen76 said:

We need to know about all the stars in the Milky Way.

Not really. You just need a statistically valid sample and knowledge of stellar populations.

Robin

On 16/12/2023 at 09:45, StarMen76 said:

For a significant breakthrough in astrometry, the sensitivity of the new telescope should really be close to 30 magnitude. For Hipparchus the limit of sensitivity was close to magnitude 10, for Gaia it was close to magnitude 20. The next step should be all-celestial astrometry at magnitude 30. While such objects are available only to Hubble and Webb, famous Halley’s Comet is now approximately the same magnitude.

Isn't Gaia distance measurement limited by the precision to which the parallax can be be measured rather than brightness? (There are plenty of objects brighter than mag 20 which are well beyond  the limits  of Gaia parallax measurement . )  Without increasing the parallax precision by for example increasing the baseline A "large aperture Gaia" would not add much new distance information, just some intermediate points from less luminous objects.

Robin

This was another good thread

The astronomer from across the pond they had on the BBC radio programme ( "inside science" or "science in action", I forget which)  likened it to the energy in a pitched baseball  so 0.15kg at say 100km/hr (a rather slow pitch ? I'm no expert on that particular sport) which would work out at ~ 0.15*28^2 / 2 = ~ 60 Joules.  That's a lot of energy of you happened to be in its way though. How much energy would it dissipate passing through your body I wonder ?

Cheers

Robin

I guess plants turning our once CO2 rich atmosphere into solid material presumably added a bit in coal seams, though by reversing the process we must be currently causing some net shrinkage. The process is perhaps detectable locally around my observatory where after a decade or so there is no longer a  gap between the bottom of the doors and  the lawn. Long term everything once on the surface ends up underground due to plate tectonics.

Robin