robin_astro

9 minutes ago, robin_astro said:

Though there have been various proposals, I understand this is beyond our current technological capability

This is an example,

https://ui.adsabs.harvard.edu/abs/2023AAS...24146307B/abstract

Though technology is being developed which might one day make it possible or perhaps achieve the even higher precision needed for space based gravitational wave measurements

https://lisa.nasa.gov/

a mission scheduled for launch mid 30's

23 hours ago, Earl said:

with greater bandwidth surly the same proces can be done with digital optical images

It is more a precision issue. The feeds from the multiple telescopes have to be kept in phase to a fraction of a wavelength (of light in the case proposed). Though there have been various proposals, I understand this is beyond our current technological capability

Robin

15 minutes ago, robin_astro said:

There are a lot of uncertainties in the calculation though

The information in this link might form the basis for an alternative calculation of when the first annular eclipse occurred

https://www.quora.com/How-long-was-a-day-during-the-dinosaurs

Robin

On 24/03/2024 at 18:11, Paul M said:

The dinisaurs lived in an era of much shorter days and there were no annular solar eclipses.

Hi Paul,

Do you have a reference for that?  According to the reference I posted above, annular eclipses first started happening about 1.6 billion years ago, well before the dinosaurs. There are a lot of uncertainties in the calculation though

Cheers

Robin

3 hours ago, Graham Darke said:

If on the other hand an eclipse occurs when the Moon is further from Earth then the Moon’s apparent diameter may not completely cover the Sun and we have what’s called an annular eclipse.

 So according to this link this first occurred about 1.6 billion years ago, the first time the sun did not completely cover the sun during (an otherwise) total solar eclipse

https://public.nrao.edu/ask/when-did-the-first-annular-eclipse-occur/

Robin

On 13/03/2024 at 17:06, Brian O said:

Faster than light inflation at the birth of the universe has always been a great problem.

What caused inflation is an open subject but why specifically is "faster than light inflation" during the inflationary period seen as a problem any more than it is now with the current rate of expansion which, depending on the coordinate system used, also implies "faster than light velocities". 

According to the description in the link posted by Andrew, inflation took place under conditions where "normal", (though extreme) physics holds.  Isn't the question of "faster than light velocities" at both early and late times therefore resolved within the framework of general relativity as Zermelo points out without the need of new physics?

Robin

https://stargazerslounge.com/topic/370302-“we-don’t-really-know-the-speed-of-light”/

The Wikipedia entry for Dark Matter pretty much covers what you are talking about. The current thinking on what it might be and alternative theories 

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

39 minutes ago, Michael Kieth Adams said:

 What makes the bits that they are made of come together?

https://home.cern/science/physics/standard-model

There are four fundamental forces at work in the universe: the strong force, the weak force, the electromagnetic force, and the gravitational force. They work over different ranges and have different strengths

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