Forum Replies Created
-
Posts
-
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.
James,
The internet seems to think it was “anecdotally” the Jacobus Kaptyn Telescope.
Best wishes,
Dominic.
James,
It basically comes down to weight, I think. Putting a big telescope on an equatorial mount isn’t possible from an engineering point of view. Mirrors that big deform under their own weight when you slew them, which you need to correct for with actuators under the surface. Alt-az is a nice coordinate system, because the deformation varies with altitude, but is independent of azimuth (if you built the telescope properly!).
Another nice feature of an alt-az arrangement is that you can direct the light off sideways to a Nasmyth platform to the side of the telescope. You can even engineer it so the Nasmyth platform never moves. That means you can make the detectors as heavy and unwieldy as you like, and it doesn’t matter. Moreover, you can have multiple Nasmyth platforms with different instruments on, switching between them simply by flipping a mirror which deflects the image off sideways. Most professional telescopes have at least two Nasmyth platforms.
As Andy S says, field rotation is a piece of cake compared to keeping many tonnes of metal aligned to optical precision!
Best wishes,
Dominic.
Hi John,
I’m sorry to hear you’re having trouble. You should be able to pay without setting up a PayPal account. When we redirect you to the PayPal website to make payment, you should see a grey button at the bottom inviting you to pay as a guest. This will allow you to enter your card details without setting up a PayPal account.
We are aware of a problem that this option doesn’t seem to be available on phones, and possibly some tablets, but is certainly there on PCs. We have contacted PayPal to ask if there’s anything we can do to help users of mobile devices.
We are also aware that the dates on the online renewal form are currently out of date — this will be corrected within the next few hours with the launch of a new and much simplified form, but you can continue to use the form in the meantime.
I hope that helps.
Dominic.
Hi David,
I’m afraid pasting from MS Word can be a bit of a minefield, yes. Word includes all sorts of superfluous formatting information when you paste into a web browser. The BAA forum is supposed to strip all of that out and just leave your text, but sometimes it doesn’t do a very good job of it.
I’ve done a quick edit on your post to remove some of the junk, and hopefully not too much of your actual text.
I personally tend to paste text from MS Word into MS Notepad, and then from there into the website. Notepad is a really simple no-frills text editor, and completely removes any formatting which may cause problems!
Best wishes,
Dominic.
James,
It’s fairly common for universities to offer short summer placements to promising undergraduates. However, they normally happen within the institution where the student is studying. I’d recommend he pesters his tutors and lecturers. They’re probably busy people, so persevere with it!
Best wishes,
Dominic.
Hydrogen alpha emission is generally stronger than hydrogen beta, and occurs at a more conveniently observable wavelength. Hydrogen beta is bluer than H-alpha, and suffers more atmospheric attenuation as well as being a weaker line.
Hydrogen alpha isn’t actually the strongest line that ionised hydrogen atoms produce – that’s Lyman-alpha. But it’s in the ultraviolet and can’t be observed from the ground, so once again practicalities get in the way.
The ratios of all these lines are interesting, but if you’re going to measure one single line, H-alpha is where you’re going to get the strongest detection.
The CNO cycle is a mechanism which produces energy in stars which are somewhat more massive than the Sun. It requires a temperature of about 17 million kelvin, whereas the Sun’s core is only 15 million K. Even in stars which are powered by the CNO cycle, it’s restricted to the very centre of the star. The visible photosphere will be only a few thousand K and what you’ll see is mostly H and He.
I’m glad we provided family entertainment with the first five questions at least :-).
This was a first for the BAA, and my co-conspirator (James Dawson) and I weren’t sure how difficult to make the questions. I was keen not to have people getting full marks, so we went for a spread from ‘difficult’ to ‘very difficult’. On balance, I think perhaps we’ll include some slightly easier questions next year!
Thanks for the feedback, everyone. When we updated the look of the image galleries a few weeks ago, it seems that page got left behind. In fact, the contents weren’t quite right, either. Sorry about that.
If you look at the page https://www.britastro.org/gallery_recent you should now see all the images in the main BAA image galleries, which are picked by our team of editors as some of the best (or most topical) observations we’ve received.
The page https://britastro.org/recent-images will show you a complete gallery of all the images that BAA members have uploaded to their member profile pages, and so will show you many more images.
I should probably at some point label those two pages so it’s more obvious how they’re different!
Hi John / David,
I’m sorry to hear you’re having trouble. It sounds like there’s a faulty web link on some page of the site, but I need a bit more information to trace exactly where it is, though. Can you let me know exactly what you’re clicking on to get this error message? Can you give me the full web address of the page with the link that’s producing this error? Alternatively a screenshot (including the web address bar at the top of your browser) would also give me what I need.
Thanks,
Dominic.
Is it working better now?
I’ve had to change the date selection interface to work around a bug in the content manager we use, but I think the new interface is possibly nicer than the old one, anyway.
For tidiness, I’ve removed the option to list “all meetings” versus just “BAA meetings”, since they’ve been showing the same listing for several years now.
Best wishes,
Dominic.
Opticians sell cheap cloths called “microfibre wipes” that are designed to get grease and dirt off pairs of glasses.
I’ve always been really impressed how well they clean my glasses, and have taken to using them on camera lenses too. I’ve never tried them on telescope optics, but I guess they ought to work? I’d be interested to know if anyone else has tried…
Hi Bill and Callum,
Sorry I didn’t reply sooner. As Callum says, I see two counters when logged in: one for views, and one for replies. When I’m not logged in, I only see the replies counter. I think that’s what has always happened.
I am currently tinkering with the forum, and hopefully you should see some common gripes tidied up later this week.
That said, my changes shouldn’t be visible to you just yet! If something has changed, please post the weblink of the page where things don’t appear right, and I’ll see if I’ve inadvertantly broken something!
Best wishes,
Dominic.
Hi Denis (and everyone),
I’ve just finished processing the other videos, which you can find here: https://britastro.org/video
You need to be a BAA member (logged into the website) to see beyond the first two minutes of each talk.
