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I’d be curious if anybody has any more information about this. The BBC contacted me yesterday asking for an interview, but I declined because I couldn’t find any information to back up their claim that “it is thought it could be a Chinese satellite called Object K”. I wonder where they got that from.
No doubt it’ll be covered in the next issue of Jonathan McDowell’s Space Report.
Hi Ken,
Interesting that you worked at Philips Research. Our paths may well have crossed in the early 2000s, when I did three summer internships at PRL. At the time I was torn between a career in astronomy versus joining Philips, but the decision was made for me when PRL closed down. Just in case the world wasn’t already small enough – I’m guessing you worked in Alan Knapp’s group? His wife taught me chemistry at school…
As you say – you can get a long way by assuming local thermal equilibrium. How far is an interestingly controversial question. Without any independent way of measuring the physical conditions and composition of a star, it’s hard to verify exactly how accurate models are.
It’s a very long time since I’ve looked at these kinds of calculation, but I think the jigsaw piece you’re missing is Kirchoff’s Law. From memory, this has the consequence that any plasma that is in equilibrium for the polychromatic case is also in equilibrium with regard to emission and absorption at every monochromatic wavelength of light. The result is that you never need to solve the polychromatic case. You solve the equilibrium equations monochromatically for every wavelength you’re interested in. As I recall, if you’re interested in solving for the equilibrium occupation probabilities of the quantum states, your monochromatic equations give you a bunch of (thousands of) simultaneous equations that you can solve with a big (sparse) matrix inversion operation. You should end up with something resembling a Boltzmann distribution.
The oscillator strengths reflect the fact that transitions are more likely between quantum mechanical states with similar wavefunctions – which give rise to strong lines – versus those with very dissimilar wavefunctions – which give rise to weak “forbidden” lines. But calculating wavefunctions is somewhere between difficult and impossible, and numerical approximation often don’t seem to resemble reality particularly well. Hence the tendency to use empirical lab measurements.
Best wishes,
Dominic
Ken,
I fear this may be a rather trickier task then you think.
The first problem is that stellar atmospheres are not in thermal equilibrium. There’s convection going on, dredging up hot gas to the surface, which then cools and sinks back down. The cooling gas is not in thermal equilibrium.
Furthermore, stellar atmospheres are translucent: light can penetrate a certain depth into the atmosphere. Temperature and pressure change with depth. This means that to model a stellar spectrum you need to do ray-tracing through a finite depth of partially opaque medium, modelling absorption, emission, and photon scattering. This is the branch of astrophysics called radiative transfer.
And to make things worse, the quantum mechanical equations for atomic line spectra are not soluble for anything more complicated than hydrogen. Computational models of bigger atoms exist, but they’re notoriously inaccurate. To be sure of what an atom’s spectrum looks like, you really need to measure it empirically in a laboratory. But that’s hard, because it involves recreating the conditions at the surface of the Sun. Atoms need to be exceedingly hot to reach the ionisation states they attain in the Sun. So you need a very large laser, some very hot and very pure samples of each chemical element, and a very fast camera that can measure the spectrum of the plasma formed after the laser fires.
To compound the challenge, there are > 100 elements in the periodic table, each of which can have N-1 ionisation states, leading to thousands of atomic states, each with distinct spectra. And that’s just the atoms – stellar atmospheres have molecules too.
I have professional experience working with a couple of codes which attempt to model all of the above, and each is the culmination of several PhDs worth of work. Turbospectrum (Bertrand Plez et al. 2012) is simpler and open source. PySME (Nikolai Piskunov et al. 2018) is more sophisticated in its modelling of non-equilibrium effects, and is available in binary form online but not open source. Both rely on the VALD list of atomic lines – maintained at Uppsala University – which is essentially a synopsis of a vast number of laboratory studies. The oscillator strengths in there are mostly not calculated by quantum mechanics; they’re fitted to empirical data. Quantum mechanics may allow you to write down equations for oscillator strengths, but that’s not much good if they can’t be solved.
I hope that’s vaguely helpful.
Best wishes,
Dominic
Dear Richard,
I fear we’ve got a while to wait for such a conjunction. By my calculations, the next will be in 2164-6 (0.8-degree separation). A graph of the angular separation of the pair around this time is here: https://in-the-sky.org/graphs.php?gtype=8&startday=7&startmonth=1&startyear=2162&duration=8&obj1type=1&obj1txt=Uranus&obj2type=0&obj2txt=Neptune
However, my calculations also suggest there was a recent conjunction of the pair (less close; 1 deg separation) in 1993: https://in-the-sky.org/graphs.php?gtype=8&startday=7&startmonth=1&startyear=1992&duration=7&obj1type=1&obj1txt=Uranus&obj2type=0&obj2txt=Neptune . I’m a few years too young to have observed that, but I’m sure there are plenty of others here who would have done!
Cheers,
Dominic
Hi Dave,
The position of the Earth’s point of perihelion is fairly random.
Over astronomical timescales, the point of perihelion undergoes considerable precession over hundreds of millions of years, and so there’s not much significance to where it happens to be right now. Further evidence that perihelion points are random comes from the fact that the perihelion points of the other planets are all in different positions around their orbits (see the attached screenshot, taken from https://in-the-sky.org/solarsystem.php , showing the terrestrial planets, with perihelions marked ‘P’).
The fact that the sun’s tilt is always reasonably close to zero is not such a coincidence – the Sun and planets formed out of a common protostellar nebula, and both the Sun and the planetary orbits take their plane of rotation from the rotation of the gas cloud from which they formed.
Cheers,
Dominic
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It’s always interesting to read this thread each year.
I find it interesting to correlate the responses above with the number of images submitted to the BAA’s online image gallery over the year (using the histogram button in the gallery; screenshot attached below).
In 2023, we saw 2,967 images uploaded by BAA members (excluding section archives), slightly down from 3,240 in 2022. But curiously, the month-by-month rate of image submissions doesn’t seem very strongly weather dependent – it was actually slightly increased during the wet autumn months, possibly driven by the start of the new deep sky season. And of course, some observers are using non-UK-based telescopes. There are some clear spikes marking the dates of eclipses and major meteor showers.
One of the most prominent features is a very clear dip in BAA observing activity over the past couple of weeks, presumably driven by a combination of Storm Gerrit, Storm Henk, and excessive mince pie consumption! 🙂
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Welcome to the forum, Christopher Baddiley. I recall seeing some of your research presented at NAM 2022, and I was seriously impressed by your systematic approach. For me, it was one of the stand-out talks at a very busy conference. It’s great that you’re doing this work, and it’s great to see it talked about in this forum.
AlanM – There is a place in space where you could observe a Sun/Earth eclipse – near the Second Langrange point (L2). Nick is probably quite familiar with it since he has worked on spacecraft that operate there. L2 is actually slightly beyond the Earth’s umbra, so you’d see a partial/annular eclipse there, but any spacecraft en-route to L2 will pass through the Earth’s shadow to get there.
Unfortunately there aren’t many eclipse observations, though. Those pesky spacecraft project managers tend to get upset if you propose to point expensive spacecraft cameras at the Sun…
I think the problem is that meteorites need to be stored in tightly-controlled clean environments if they are to remain scientifically useful. It would be very costly to put a meteorite on public display without contaminating it. The NHM would be kicking themselves if they put a particular meteorite on display, only to discover they’d spoiled a specimen that subsequently turned out to be of scientific interest.
This is a dilemma the NHM faces with other exhibits too. I remember my disappointment when I visited a few years ago, to discover they’d removed all the fossilised dinosaurs I remember gaping at as a kid. Of course, what I hadn’t realised as a kid was that original fossils are far too precious to mount for display, and so the ones I had gaped at were all rather dubious plaster models.
Having made many of the BAA’s meeting videos in the past, I would re-iterate what James and Andy have already said. It can be pretty time consuming.
In theory, it’s simple enough to wire the speaker up with a microphone, and insert an HDMI recorder between the laptop and the projector.
But that’s just the beginning.
When you get home, you’ve got a hundred GB of raw video. That needs sending (by post?) to somebody with access to (inevitably, very expensive) video editing software. First, the audio needs synchronising with the video. Inevitably, if the footage was shot by a novice, there will be problems with it (e.g. the speaker was breathing into the microphone, the microphone wasn’t turned on, etc, etc) which need to be identified and worked around. Eventually, once you’ve spent a couple of days fixing everything, you do an export to compressed web-ready video. That takes many hours of CPU time in itself.
Then, you circulate the video, and discover somebody showed copyright material on one of their slides, and you get asked to cut something out. So you have to re-export the video – which is another overnight job.
I’m as supportive as anybody of the BAA filming talks, but it’s a lot of work to expect anybody to do on a voluntary basis. And for the same reason, companies that do this professionally are also not cheap.
Sad news, indeed.
I didn’t know Tom personally, but many of my colleagues did. The past couple of months have been an extremely difficult and upsetting time for them, and everybody connected with Warwick University. Tom seems to have been universally liked and admired by everybody who had the good fortune to know him.
It has been apparent for some weeks that the chances of his survival were extremely slim, given the extremely harsh environment of the Atacama Desert. I’m told by colleagues who have visited La Silla that going out for a walk is usually strictly prohibited without careful preparation and regular radio contact. I suppose the one positive from today’s news is that at least there’s now some closure for his family and friends.
RIP Tom.
Thanks, Alex – that’s really useful. It’s always nice when somebody else has already done the difficult calculations! 🙂
Hi Robin,
While the web-ops group did put quite a lot of effort into trying to avoid broken web links, unfortunately it seems we didn’t catch all of the variant web addresses that some pages have.
The canonical form of the address of pages in the old Drupal site was <https://britastro.org/node/25856>, where 25856 is the page number. I believe all these canonical URLs should correctly forward to the right page in the new site, including this one.
But as you have discovered, unfortunately the “node” bit could sometimes be substituted with other words in the old site, and many of these alternative page addresses no longer work.
So, if you’re trying to fix a broken link, you can generally find the page you’re looking for by changing the broken link into the canonical form and seeing where it redirects to in the new site.
Best wishes,
Dominic
My tuppence worth…
Anyone writing a planetarium program has an interesting challenge when looking for a catalogue of informal names to display next to deep sky objects.
Since 2016, the IAU has maintained a list of “official” names for stars – an effort led by Ian Ridpath. Before 2016, there wasn’t even a canonical list of names for stars. The author of every star atlas would have to make up their own mind about which names were canonical and which ones were just silly.
There is no corresponding list for deep sky objects, and if you try searching the internet for a catalogue of common DSO names, most of what you find is junk. I speak from hard experience, since the BAA image gallery tries to display the common names for DSOs where possible.
The BAA image gallery uses a hand-created list that I’ve built over the years, and which is probably highly incomplete. I imagine the authors of Stellarium wanted a more complete list, which meant they were probably stuck with crowd-sourcing their data. And when you crowd-source data… of course you sometimes get bad data.
I agree the BAA site has been quite quiet over the past couple of months, though traffic on this site has always been rather variable, and midsummer is usually a sleepy period.
So, I’m not overly concerned and I suspect what we really need is for a naked-eye comet to come along. 🙂
But of course, if there are reasons why people are finding it difficult to contribute, please do let the website operations team know – either on the forum, or by private message. We can’t promise immediate changes, but we will certainly give serious consideration to any feedback we receive.
I just attempted to upload a GIF movie to my image folder and although it played properly it continually flashed in its thumbnail form,it was so bad I have had to delete it before I cause epileptic fits or seizures. Would it be at all possible to include WMV movie format (obviously still within the 2 megabyte size limit)?
Hi Alun,
I’m sorry to hear you’ve been having trouble.
There is a bug that I’m aware of that the teaser images for GIF animations can sometimes get messed up in the way you describe. Unfortunately this is a bug in the underlying software that is used to generate the thumbnails (ImageMagick), and so I think it’s rather difficult to fix without switching to using different software, which would clearly be quite a large job. It’s on my to-do list to look into it, but unfortunately fixing it is likely to be a long-term project.
Unfortunately, we’re also unlikely to allow members to post video files into the BAA image gallery in the near future. While I realise this a frequently-requested feature (it’s already been discussed in at least one other forum thread recently), hosting galleries of video files is a very different problem to hosting image galleries. The trouble is that video comes in all sorts of different formats (WMV, MP2, MP4, OGGV, WEBM, AVI, MOV… to name a handful that come to mind). Most of those are not compatible with all web browsers and operating systems. In fact, the only ones which are (almost) universally compatible are MP4 and WEBM. Even then, you need to use very specific encoding settings (called H.264 if you want the full gory details), and so if we allowed users to upload MP4 files, we’d doubtless receive files some people couldn’t view. Websites like YouTube have very clever software behind the scenes which converts whatever video file you upload into an appropriate format that the viewer’s computer can accept. So, in order to allow video uploads to the BAA site, we’d need to do an awful lot of work to reproduce that. And we’d no doubt receive lots of user feedback that such-and-such video file wasn’t working, for some deeply technical reason.
So, for the time being, I think our advice remains that it’s best to upload your videos to a personal YouTube account, and then you can post a web link to it in the BAA Observation Gallery, along with a still image from the video.
Sorry we can’t be more helpful currently,
Dominic
https://britastro.org/observations/observation.php?id=20181111_015500_44cd9ab1092010e3 contains a reference to https://britastro.org/node/19348 (this is just a specific example of no importance otherwise), which link is now broken. I can easily fix isolated examples in my own pages but perhaps they may be corrected globally with a script? AFAICT, and assuming the old pages are still available in an archive somewhere, a relatively straightforward pattern matching exercise should match old with new URLs.
Hi Paul,
We already have a script which does this, but apparently it’s not working properly. I shall flag this up with the relevant individual.
Cheers,
Dominic
From William’s description, my guess would be that the web server is not allowing partial-content downloads, and so the video player is not able to start downloading the video file part-way through. Hence, it has to download the whole preceding part of the video before the jump facility starts working.
If this is the problem, it may be fixed by some lines like the following in the relevant htaccess file:
Header set Access-Control-Allow-Origin “*”
Header set Access-Control-Expose-Headers “Content-Type”
Header set Access-Control-Expose-Headers “Accept-Encoding”
Header set Access-Control-Expose-Headers “Range”… with the last line being the particularly important one. However, WordPress possibly has a switch somewhere for controlling this behaviour.
I vaguely recall seeing exactly this same problem on another website, many moons ago… possibly the previous BAA website, in fact!
Hi Nick,
This was not a conscious decision, and I agree it’s a bug. What’s happening is that we are rolling out off-the-shelf solutions – which typically come with default restrictions which may not be appropriate to the BAA – and then looking at what configuration changes we need to make.
This iterative process may move a little slower than many would like, since we currently have around 30 open bug reports and a relatively small team working through them. But I have passed your feedback on to the relevant individual who I’m sure will get it fixed as soon as he can.
Cheers,
Dominic
