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Arrrgh! I fear I’m at least partly responsible for this. Some of the article looks like a mangled version of what’s on my website. My website says that the comet rises at 21:15 BST. I assume the summer student who wrote this article cut and pasted the rising time as the best time to see the comet.
A couple of weeks ago I changed the algorithm used by my website to decide when to list comet apparitions as news events. This resulted in some very bad predictions, which I commented on in a previous forum post. Martin and Nick convinced me I needed to fix this, but I haven’t had time to get it changed yet.
I really need to get on with it… sigh…
Hi Martin,
Thanks for the reply. It’s good to know that I’m not alone.
My reaction would be to query what the point of publishing these absolute magnitude values is, if the numbers produce such wild predictions. Surely, the only reason to publish absolute magnitudes is for people like me to use them to predict the future brightnesses of comets. Isn’t it inviting naive people like me to start telling the world that Blanpain will be a fifth magnitude comet?
In the past I’ve heard people express exasperation when comets get over-hyped, only to disappoint. And so, wouldn’t it be better to publish absolute magnitudes at the conservative end, rather than ones that lead to wildly optimistic forecasts? It would help if there was any kind of error bar quoted, to signify which absolute magnitudes are vaguely trust-worthy.
I should add that the absolute magnitudes on the BAA Comet Section pages are much more reliable than those on the MPC website – I suspect in part because the BAA only publishes values for moderately well-behaved comets. The BAA does not, for example, publish any values for Blanpain.
Even then, by my calculations, the BAA’s published absolute magnitude for 2017 T2 puts it at magnitude -1 next May, which is about 5-6 magnitudes brighter than most people seem to be expecting.
Best wishes,
Dominic
A correction to my previous post. Seen from the Sun, L4/5 are both 60 degrees away from the Earth. Seen from the Earth, L4/5 are both 60 degrees away from the Sun.
The Sun, Earth, and L4/5 form equilateral triangles, with all three interior angles being 60 degrees, and all the sides being 1 AU.
L4 and L5 are almost exactly 60 degrees away from the Sun [*], along the plane of the ecliptic, I think?
I say “almost” because as you point out, the Earth’s elliptical orbit will presumably perturb that angle slightly over the course of the year, though I imagine the perturbation is tiny.
[*] — My original forum post was incorrect, so I have edited the wording.
Due to the slightly weird way that Drupal works, error messages often get delayed until the next page you view after the one that generated the problem. So you could see these errors on any page of the site, if you view that page immediately after visiting one of the troublesome forum posts.
For the time being, I’ve installed a filter which I think should be hiding these errors. The errors are still happening, which isn’t ideal, but I think you shouldn’t see them any longer.
Roy,
About 10 days ago I installed a security update to the forum software that we use, Drupal’s Advanced Forum package.
Judging from the discussion forums associated with Advanced Forum, they mucked something up in a security update, so a lot of Drupal websites are currently being plagued by these errors.
It’s unlikely to be affected by which web browser you use. I think it’s fair more likely that it will occur on a few specific forum posts which unluckily happen to trigger this error condition.
Being free software, Drupal unfortunately tends to take its time about fixing problems, so I wouldn’t hold my breath for a quick fix to this. We do have the option to remove the latest security update if this becomes a really serious problem, but I’d prefer to avoid doing that if at all possible!
Best wishes,
Dominic.
David,
I have likewise not found any information about how the USNO calculate the values, or how accurate they are, though I have admittedly not looked very hard. I would expect they’re pretty good, though. I’m sure somebody like Jean Meeus would have noticed by now if they were publishing times that were wrong!
I think that if the times are computed using the most accurate data available, one-minute precision should be easily achievable. Both the Earth’s orbit and its rotation are very well characterised. Its rotation is measured by monitoring distant quasars with radio interferometers, which can achieve micro-arcsecond precision. That precision is required by Gaia, for example, which is doing astrometry at micro-arcsecond precision in a coordinate system defined by the Earth’s rotation axis.
The Earth’s orbit is very well characterised from spacecraft tracking work (Nick James’ day job). The idea is to track the position of spacecraft by measuring the time taken for telemetry to reach them from ground stations. In extreme cases (e.g. Rosetta) this has been done to one-metre precision or better. That requires you to know the position of each ground antenna to one-metre precision, which is no mean feat as that’s below the scale of seismic oscillations in the Earth’s crust…
So my guess would be that the Earth’s orbit is known to about one-metre precision, and the position of the celestial poles is known to micro-arcsecond precision. Of course, that’s not to say the USNO used an ephemeris that was that good. I would think it’s very likely they used some publicly-available ephemeris of lower accuracy.
Yes, I agree that amateur transit surveys are tantalisingly within reach. The hardware used by most of the ground-based professional surveys is basically high-end amateur kit. Though, crucially, with professional-grade CCDs, dark sites, and many years of software development to pull out ridiculously small signals from the photometry.
I am doubtful about the prospects for amateurs discovering even hot Jupiters by themselves. The professionals have been at this game for a couple of decades now, and I suspect all the really conspicuous transiting objects have already been found. There are bound to be plenty remaining with long periods, but amateurs will have the same difficulty as professionals that you’re unlikely to happen to be looking at the right star at the right time to record very infrequent transits (bearing in mind you have to see at least 2-3 transits of the same planet to convince anyone).
Doing follow-up on known targets sounds like a far more realistic prospect.
Though, of course, I invite you to prove my scepticism wrong! 🙂
I was about to say that I could think of few reasons why anybody would need to know the time of the equinox to the nearest minute, before realising a rather entertaining set of circumstances took place last night…
* Wed 20/03/2019, 21:58 UTC, March equinox.
* Thurs 21/03/2019, 01:44 UTC, Full Moon.The date of the equinox is used in the calculation of the date of Easter. To quote Saint Bede (The Reckoning of Time, 725), “The Sunday following the full Moon which falls on or after the equinox will give the lawful Easter.”
As I understand it, the church mucks up the calculation by defining the equinox to occur at midnight on 21st, and further defining full moon to occur 14 days after new moon.
Perhaps the BAA should start a campaign to “get back to Bede” and celebrate the astronomically-correct date for Easter this weekend.
To answer your actual question…. my impression is that these times are calculated by the US Naval Observatory and printed in the Astronomical Almanac, and that basically any and every source that quotes times for the equinoxes and solstices get them from the AA. So, I think if 21:58 is what the USNO says, basically that’s the time that everyone will quote.
I’m not sure what algorithm the USNO uses. When I have tried to do the calculation myself — which I tried to do in order to put equinox times on my website, In-The-Sky.org, I struggled to get exactly the same tiime as the USNO. For last night’s equinox, I get 21:44 UT. A difference of 14 minutes is larger than I would expect, since I used the NASA DE405 ephemeris to get the position of the Earth and Sun to high accuracy. I suspect I screwed something up — quite possibly there was an inaccuracy in my correction for the precession of the equinoxes (which is necessary to get the Sun’s RA and Dec for the epoch of the equinox, not J2000 coordinates).
I struggle to see how you come to that conclusion, Roger.
On the ground, professionals have NGTS, WASP, HAT, KELT, not the mention several smaller exoplanet search programs. In space, professionals have TESS, soon to be joined by CHEOPS, and later PLATO. Right now, professional exoplanet search programmes are incredibly active, and will remain so for at least the next decade. Probably far beyond.
There’s relatively little professional effort going into biosignatures, because it’s basically impossible to detect them with current technology. Yes, people have pointed large telescopes (e.g. the VLT) with high-resolution spectrographs at bright stars, and picked up spectral lines in exoplanet atmospheres (NB: abundant things like water, not “biosignatures”). It’s impressive work, but only possible for a handful of the brightest stars, orbited by very large planets. When the ELT comes online in 2024, it will be possible for more stars, but we’ll still be talking about molecules like water and methane in the atmospheres of small numbers of giant planets.
I’m puzzled by this talk of amateur opportunities for the “discovery of exoplanets”. The best amateurs can achieve right now is to observe predicted deep transits, if they squint really hard at their photometry. That’s already very difficult, and far short of actually discovering a transit you didn’t already know about. Perhaps you’ll prove me wrong, but I’d consider my money pretty safe if I bet that there will be no amateur exoplanet discoveries in the next decade. Unless you plan to build a replica of the NGTS in your back garden…
Back in 2000, the RAS published an article about Pepys’ astronomical activities in their magazine A&G.
You can read it online here: http://adsbit.harvard.edu//full/2000A%26G….41d..23W/D000023.000.html
As I understand it, telescopes of this era were always measured by focal length, rather than aperture. So “12 feet” does indeed refer to the length (similarly, Herschel’s “40-foot” telescope had that focal length). The instrument apparently cost Pepys the small fortune of £9.
The article also points out that Pepys’ activities with optical glass went beyond astronomy… 26 May 1667… “I did entertain myself with my perspective glass up and down the church, by which I had the great pleasure of seeing and gazing at a great many fine women…”
My guess would be that they made the figure in some tool like Adobe Illustrator, and while they were manipulating the labels into the right places, some numpty accidentally pressed the delete key with the wrong object selected. As Alex says, it looks like some amount of the outline is still visible, so possibly they even deleted the orange fill without deleting the outline. Or they were fiddling with the settings for the dark shading where the eclipse is visible, and accidentally had Britain selected at the time. 🙂
Well said, Tracie.
It’s dangerous to assume that ancient observers had anything like the mindset of a modern amateur astronomer.
The ancient Greeks were so certain that the sky was unchanging that they insisted novae and comets were inside the Earth’s atmosphere. The experiment that Tycho Brahe did to disprove this wasn’t technically difficult — he simply measured the parallax of a nova and showed it was less than the Moon’s. The reason this had to wait until the 16th century wasn’t lack of technology, it was just that nobody was asking the right question.
I don’t doubt that in the whole history of Australia, there wasn’t some bright spark who said “Hey, Betelgeuse looks bright tonight!”. But that doesn’t count as a “discovery”. We don’t say that Hipparcos or Flamsteed “discovered” Uranus, simply because they observed it and marked it on star charts. We credit the discovery to Herschel, because he was the first to realise it wasn’t just another a faint star.
As Tracie says, ancient people probably ascribed any variability they observed to sky conditions. In most cases, that was probably the correct interpretation. In the absence of any evidence that their thinking went deeper than that, I think it’s nonsense to speculate further!
Roger Dymock: The main technical difficulty with creating live streams of meetings is that we need a very reliable and fast internet connection at the meeting venue. A dodgy Wifi connection isn’t good enough: it needs to be a rock solid wired connection.
Surprisingly few venues offer this. The internet in Burlington House is not great, and when we enquired about live streaming the Christmas meeting at UCL a couple of years ago, even that was a no go. I very much doubt Sparsholt College would be able to help us, unless they already do live streaming themselves.
In my opinion, doing this badly is probably worse than not doing it at all. If we offer a live stream, and then it keeps breaking up and isn’t actually watchable, we’re sure to annoy lots of people. So, on balance, I think it’s best to focus efforts on what we know we can achieve, which is high-quality videos of meetings after the event.
It’s a little while ago now, but David Arditti gave a memorable review of Hyperstar at the 2011 Deep Sky Section meeting. I happen to remember it because I wrote the meeting up for the Journal.
If you hover over the “Publications” tab at the top of this website, and select “Downloads”, and then go to “Journal Archive”, and then “2011 August”, you can find my write-up of David’s talk starting on page 245.
I don’t know whether the technology has moved on since 2011, or whether David’s opinions have changed, but the impression he gave seven years ago was that Hyperstar was a bit of a nightmare to install / use!
The website behind this (LEVEL5) is indeed very ancient, but it also has some very good stuff on it. It’s well worth having a look around what they have — I still routinely refer back to their cosmology tutorials whenever I need a refresher.
As I understand it, this was a NASA project in the late 1990s to make astronomical tutorial texts freely available on the web. Clearly a lot of effort was put in at the time: they are often written by authoritative authors and are clear and accessible. However, it looks like funding must have dried up in the early 2000s, and since then it’s become of museum piece.
My experience of weird USB configurations has tended to be that Linux seems a lot more tolerant than Windows. I’m guessing the kind of people who play with Raspberry Pis are much more likely to play with USB-over-ethernet, USB repeater-extension cables, etc, than the average Windows user. So I’m not sure it’s fair to assume that just because this hardware works under Linux, the same will be true of Windows! 🙂
This is a good question which I suspect many people wonder about. A lot of good things seem to quietly go on within the sections, which perhaps we could publicize better.
I recently ran a search on NASA ADS for refereed articles featuring John Rogers (Jupiter Section) as a co-author, and was really impressed by the number and range of papers which came back. John’s publication record is better than that of many professional astronomers I could think of. It’s not just John – if you key in the names of other leading BAA observers, you likewise get impressive lists of papers.
There have been proposals to put together an up-to-date summary of the BAA’s ProAm activities somewhere, which I think would be very welcome.
Another idea was to have a “Projects” area of the website, summarising ProAm observing projects people can get involved in. My only hesitation there is that many BAA members may not be that advanced yet, so it’d be nice to advertise easier options as well and have something for everyone to get involved in (including a paragraph about how the observations might be used). Perhaps rather than running one Observers Challenge on the homepage every few weeks, we should encourage all the sections to have a few of them, which run indefinitely. We could still pick one to feature on the front page each month.
Alex: once the video digitiser has de-interlaced the video, don’t you effectively get 25 frames per second — i.e. 0.04s resolution?
This is what my USB digitiser was delivering.
The time signal should be very accurate if it’s done competently. 🙂
There’s a caveat here that if you rely on the GPS unit spitting out NMEA data, that comes in ASCII format over a slow serial connection. By the time it’s made it down the wire and through your serial buffers, you’ll probably only get ~ 100ms timing precision.
The GPS chip will also produce a PPS signal, which is pin which gives you pips once a second, on the second. Using the GPIO lines on a RPi or Arduino, you can sample that at high frequency to get a very good time standard.
My Polish isn’t very good, so I don’t understand much of the attached webpage, but it seems to mention PPS towards the bottom, which implies this particular box ought to have much better than millisecond precision.
