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Paul: Almost entirely agree. Where we may differ is in the level of understanding required. One needs to know what those words mean but one does not need to be able to conduct original research in those fields. What is required lies somewhere in between. In my opinion, anyway.
That’s a major reason why I recommend MTW. It not only defines those words, it gives a relatively gentle introduction to what they mean and how to use the concepts in practice. Though, to be fair, Lagrangian dynamics is (IIRC) treated in the advanced track and can be skipped on initial study. An STEM undergraduate level of group theory is undoubtedly very useful but may not be strictly necessary. Again, IMO.
It is not unusual for pedagogues to disagree on details. What is unusual is for them to agree on all the details.
A few minutes ago I learned of the death of Jim Hartle.
Hartle’s book on GR, Gravity: an Introduction to Einstein’s General Relativity, also has an extensive fan club. I happen to prefer MTW but please take a look at Hartle to see if it is more to your taste.
In my view, by far the best book on GR is known as MTW amongst those who study the subject. For everyone else it is “Gravitation” by Misner, Thorne and Wheeler. A web search on “MTW Gravitation” will turn up plenty of useful links.
It is now 50 years old so misses recent developments such as gravitational wave astronomy (though it does cover gravitational waves themselves), chunks of modern observational cosmology, more treatment of alternative theories to GR than would be taught these days, and so on. However, for a thorough grounding in GR it still can’t be beaten in my opinion.
Beware, though, that this is not a book for the faint-hearted dilettante. It’s roughly 1300 pages long, can do double-duty as a door stop, and assumes a background knowledge appropriate to a physics graduate. (That said, I don’t have a physics degree but Oxford chemistry appears to have been sufficiently rigorous.) Some sections are clearly marked as being at a significantly higher level of difficulty; all of these can be skipped without missing anything important for those who want a more gentle introduction.
Ken: sounds like you have the physics background to cope with this work. I’m pretty sure that you have a better grasp of classical electrodynamics than I, for example, based on what you write above.
Paul:
I was pretty sure you would would be well acquainted with the field. My post was addressed primarily to those who are not (yet) so well informed. That’s why I took care to include easily accessible links to alternative theories.
For my part, Wolfram may well be on to something useful but he is a very long way from a theory of everything and I suspect that he agrees with me. My suspicion is that a paradigm shift will be needed for a successful merger between quantum fields and GR as a set of functions over a 1+3 dimensional continuum. The shift is likely to be as profound and disruptive as that which separates Newtonian/Galilean mechanics and quantum field theory as descriptions of the motions of particles.
FWIW, Stephen and I have known each other since 1982 and still keep in touch occasionally.
Paul: a very nice summary!
There are other approaches to QGD. the Wikipedia article on quantum gravity lists a couple of dozen or so.
Stephen Wolfram and I have long thought that the universe may be a cellular automaton with as-yet unknown rules. A recent development by Wolfram posits that the fundamental quantities in the cellular automaton may not be occupancy (as in the classic Game of Life) but graphs. The rules convert a parent graph into another for its child. https://www.wolframphysics.org/technical-introduction/ contains a simple but lengthy exposition of his ideas. https://www.wolframphysics.org/ itself gives links to a wide variety of related topics.
As to the choice of software, I can personally recommend the Tycho Tracker software.
I am a great fan of Russ Laher’s APT (Aperture Photometry Tool) and use it for my VS work. There is a good overview at https://en.wikipedia.org/wiki/Aperture_Photometry_Tool which includes a link to the official site. The software is free and runs on all common operating systems.
From ATel 16050:
We searched the HST archival data for the progenitor of SN 2023ixf. A clear
source can be seen at the SN position (https://antares.noirlab.edu/loci/ANT2023l4lgj6bhp4rt)
in the F814W image from the HST program 9490 (PI: Kuntz), which was observed
on UT 2002-11-16. The source is, however, not visible in the bluer bands
(F435W and F555W). We measure a preliminary F814W magnitude of 24.39+/-0.08
for the source. Considering it as the candidate progenitor of SN 2023ixf
and using a distance modulus of 29.05 for M101 (Shappee and Stanek, 2011,
ApJ, 733), we obtain an approximate absolute magnitude (no extinction correction)
of -4.66, which is in line with a supergiant progenitor.Payment now successful via PayPal. My thanks to Andy and the BAA Office for their assistance.
I have not posted the BAA’s PayPal account name because of a specific request not to,
Paul
Hi Andy.
Received your mail, thanks.
When that link is clicked the browser still shows an endlessly spinning arc of a circle inside the large blue button. This with “Firefox 113.0.1 (64-bit) Mozilla Firefox Snap for Ubuntu canonical-002 – 1.0”.
Oh well.
Paul
Ian: this sounds most interesting!
Can your driver be used under EKOS?
Perhaps we could discuss this in greater detail by email rather than clogging up the BAA fora.
If you feel up for a real challenge, you could write an INDI driver for the Velleman K8055 series of boards.
This would be a highly non-trivial undertaking but one which would win you kudos with a wide selection of the amateur community. People have been asking for one for years.
At the moment domes with a Velleman controller, mine included, can use only the LesveDome ASCOM controller. The problems with LesveDome is that the source code is unavailable, it is Windows only, and is ASCOM instead of the much more portable INDI.
Yesterday I purchased a Velleman WPI110N (the latest release of the K8055 series) with a view to seeing whether I can persuade it to play ball without having to perform potentially dangerous tests on a live dome.
I call the AAVSO API to get me the VS data and the candidate comparison stars in a requested mag. range and chart width. I use the B-V from SIMBAD to give me a guide to any major differences that there might be in the B-V values of the comparison stars. It’s more of a sanity check
So there is a Sanity Clause after all!
I use it to get the B-V of the target star. I couldn’t find that in the AAVSO data.
Ah.
When I add a new star to my program, I go to https://app.aavso.org/vsp/ and fill in the appropriate fields (Star, FOV, orientation, limiting magnitude, and more) and first get a finder chart, which I print for use at the telescope.
Next the photometry for the sequence in the filters required is downloaded. The B-V values and their errors are provided whether you want them or not, in line with the bottom of the VSP page where we find the words: “V and (B-V) magnitudes are always displayed. Select any other bands you wish displayed below.” A Perl script subsequent mungs the photometry data into a format useful for my current processing pipeline.
I never take a given B-V of the target star as gospel because it can itself vary as the brightness changes. If I want to know a colour index of a VS at a particular epoch I measure it for myself.
Paul,
The sequences for the BAAVSS visual charts have all been entered into the database. When you try to upload a visual observation, it’s checked against the sequence.
[Deletia
If you use an AAVSO chart, our DB doesn’t have any sequence information for these charts.Ah, there’s a thing.
In principle the AAVSO sequences could also be added to the BAAVSS database (assumng they are not there already – I don’t know). Those of us doing ensemble photometry generally include the (instrumental,catalogued) values for the (magnitude, error) of those sequence members which are measurable.
In principle, the BAA database could run sanity checks using those sequences too. Either that, or I am missing something.
Further, the AAVSO database could be scraped occasionally (once a year perhaps) to see what comparison stars have changed. What to do after a change should be obvious — pretty much what happens for BAA sequence changes.
Personally I like the AAVSO charts and lists of comparison stars because it’s easy to query via my Python code via the AAVSO API. I combine that with SIMBAD/VIZIER data to get other parameters of the target star and I can then create a good list comparison stars for ensemble photometry.
That is essentially what I do, though my code is wrotten in Perl rather than in Python.
By and large I download only the V photometry but include B and R as required. B-V, which is provided regardless, give B magnitudes but not, alas, their errors. My ensemble photometry code does The Right Thing with reported errors, which is to add in quadrature.
Out of interest, what SIMBAD/VIZIER data do you use? For my purposes all that is required is the magnitudes and the coordinates, all of which is provided in a single download from AAVSO.
My concern is that perfectly good data elicits a warning. I freely accept that the important stuff (magnitudes and their errors, star ids, date-time. filter, explen) goes through after checking. It’s the appearance and untidiness of an essentially useless warning that irritates me.
Perhaps if the chart ID was in a standard format (/^AAVSO X.+$/ for those who recognize Perl-style regexps, the database checking software could avoid issuing a warning.
Paul
Sure.
I mentioned it because I am thoroughly sick of being admonished by the VSS database for using non-kosher chart IDs.
Big hint there 😉
