Forum Replies Created
-
Posts
-
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.
I’d be interested to hear how you get on with this.
I spent 18 months playing around with Watec cameras, using Raspberry Pis and USB video capture dongles to hunt for meteors. The project in an abeyance at the moment, and to be honest I’m not sure the USB video capture hardware was up to the job. Essentially, your video signal is mostly black, and as I understood it, the cheap capture dongles were turning the gain up way too high so we were mostly recording noise. Any real structure was totally saturated. As I understand it, better video capture hardware has brightness controls that let you adjust these things.
Having had that experience, I would be wary of putting anything in my signal chain between the camera and my digitiser. I’d want to know exactly what the video time inserter is doing. If it’s passing the analogue signal through, maybe it’ll be fine. If it’s digitising the signal and then converting back to analogue, I suspect it’ll be a disaster! 🙂
A good place to start with number (1) is the BAA Handbook. Pages 28 and 29 of the Handbook for 2018 lists daily moon rise and set times for the UK.
You can also find tables of rising and setting times for the Moon here: https://in-the-sky.org/ephemeris.php?irs=1&ima=1&iph=1&objtype=1&objpl=Moon
As Robin says, the answer is the 1920s.
The turning point is often dated to the “Great Debate” of April 1920, when Shapley and Curtis publicly debated whether the “spiral nebulae” — i.e. what we call galaxies today — were part of the Milky Way, or further away.
In fact, the debate only really gained its historical significance a few years later, around 1924-5, when Hubble demonstrated the spiral nebulae had to be much too distant to be part of the Milky Way.
The significance of the Great Debate is that it was the last time that anybody could argue against the existence of external galaxies without being obviously wrong.
I too shall follow this with interest.
I built myself a ~ £300 3D printer a couple of years ago. One tricky issue I came across was the accuracy of the printing. I never really achieved better than 0.2mm accuracy. So, mechanical components generally needed a lot of cleaning up with a file before they were usable. I didn’t have much luck fine tuning the calibration, but perhaps I was just incompetent. 🙂
As regards mechanical strength, I think you almost certainly want to be using ABS. I found that my PLA prints couldn’t be left in tension for more than about a few weeks (depending on thickness) without snapping. This improved somewhat if I made the infill 100% solid, but at the expense of using lots of plastic and taking ages to print. I gather that PLA degrades and deforms particularly fast if exposed to moisture, so in a dew-laden observatory, I’d certainly favour ABS’s chances!
There even seemed to be differences between suppliers. The plastic I bought from RepRapPro (sadly now defunct) seemed noticeably stronger than what I got from various other suppliers.
While 3D printers are a lot of fun to play with and they’re great prototyping tools, I think making a precision spectrograph is quite ambitious!
Thanks all! The message I seem to be getting is that iOptron in particular isn’t a great buy. Further to Roger’s comments about screws coming lose, I was interested to find one blog post where someone was complaining that if you loosen the azimuth adjust screws too far, the mount comes off the tripod and your camera falls on the floor. Great! 🙂
I’m afraid we currently don’t support animated GIFs. I think if you try to upload one, you will only see the first frame of the animation.
Technically, this restriction is imposed by the Drupal content management system we use. Its image processing modules don’t support animated GIFs.
From memory, with a bit of hackery we could work around those restrictions. I understand that for applications like showing transient objects like variable stars, and the rotation of planets, they’re really useful. However last time this was discussed it became apparent that animated GIFs are quite polarising and a number of people really don’t like them.
So, as things stand we don’t support this, but we are aware of the feature request.
It’s noticeable how little ever seems to have been said about the incident, so everything is “anecdotal”.
The navy seems to have been understandably embarrassed by the incident — fighter jets aren’t supposed to get lost at sea.
The Jacobus Kapteyn Telescope was part of the Isaac Newton Group of Telescopes, which was (until 1998) owned by the Royal Greenwich Observatory. For a long time, the Royal Greenwich Observatory was run by the Admiralty. I’m not sure whether that was still true in the 1980s — I think not — but the two organisations still had close ties.
So, the telescope may have effectively been navy property and I suspect the astronomers would have been disinclined to publicise their patron’s embarrassment.
A Telegraph article from 2007 (when the MoD archives were released) says the ship’s owners did indeed receive a £570k salvage payment from the Navy, which I’m guessing would have also included a confidentiality clause.
