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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.
I’d also be interested to hear from anyone who’s getting good meteor captures with the Watec 902H.
If I recall correctly, the AGC only has low and high settings. As Callum says, the low setting is very dim, so you only record fireballs. The high setting is very noisy. If you stack the frames for 30 seconds you can get some nice deep images, but for meteor searching it’s not great, because the meteors are lost in the noise.
My solution was to upgrade to a Watec 902H2 Ultimate, which has an AGC knob, so I could tune the gain to a happy medium. But I do gather others are getting on OK with the 902H. I was wondering whether some kind a pre-amp between the camera and the digitiser would help, but Callum tells me he’s tried that and it hasn’t helped!
Have you tried dropping David Rothery a quick email? I’ve not corresponded with him personally, but I understand he’s very supportive of the BAA.
Hi Dave,
There may be other people here who know more about aviation than I do, so my views are my own and may not reflect the wider BAA!
I’m sure we’re all keen to make sure everybody knows that lasers are dangerous, and have to be used in a safe and legal way. The police have been doing a good job of raising awareness of this in the UK media in recent days.
However, I’m not sure NOTAMs are the way forward.
My personal understanding is that (at present) NOTAMs have to be issued for fixed laser displays, such as the ones that light up the sky at Greenwich and other temporary installations. Those installations are permanently on, so pilots need to avoid flying through the beam.
Star parties are a bit different. There’s someone steering the beam. Planes are easy to see at night time, especially at low altitude. Anyone running a responsible star party should be keeping an eye out for them and make sure laser beams stay well away. In fact, there’s a legal obligation on them to do so (quite rightly!).
If the Civil Aviation Authority wants notification of star parties, I’m sure we’d be keen to help in any way we can. However, I rather doubt the CAA could do anything useful with that information. Laser beams at star parties move all around the sky, crossing vast areas of airspace. The CAA is unlikely to block out such a large area of air space because of one star party!
So, my impression is that we need to urge people to act responsibly within the existing rules, and make sure that everyone knows that pointing lasers anywhere near planes is a very stupid thing to do!
I did at one point briefly consider using an SBIG AllSky-340 camera for my own meteor camera work (instead of a Watec 902H2 Ultimate).
Unfortunately there were lots of reasons why it didn’t really seem to fit the bill. Even though you can set custom exposure lengths, it communicates with the PC via a slow serial link, making quick exposures almost impossible. By contrast, the Watec camera delivers 25 frames per second. As Jeremy says, you really need that many frames to catch fast meteors.
The other issue is that having bright lights in the field of view is a real nuisance. You get blooming and internal reflections. The slightest muck on your glass gets illuminated. A limited field of view actually helps keep unwanted light out — the metal CCTV housing acts as a lens hood.
It was a real shame, because I wanted an excuse to buy an AllSky-340 to play with 😉
We currently offer the videos in two formats: MP4 and OGV. The MP4 is high-quality video that Nick produces with clever compression. I produce the OGV versions from Nick’s files, with less clever compression and generally much poorer video quality.
When you view the video through the player that’s embedded in our website, your web browser is given a choice of which format to play. Firefox and Chrome can play both formats, but will generally pick the lower quality OGV. Internet Explorer will play the MP4, because it doesn’t support OGV. A few platforms will play the OGV because it’s the only format they support — specifically Opera, and some (many?) Linux systems which don’t include MP4 codecs.
It’s a bit like the old VHS vs Betamax video tape wars 🙂
We have various options. We could scrap support for OGV, meaning that most users will see the higher quality video, but a few users may be left out. We could still give them an OGV they can download separately from the web player.
Alternatively, I could double the file size of the OGV files. Currently I aim for 100 MB per hour of video. We’re not close to any bandwidth limits on our server, so we could comfortably serve higher definition videos… providing BAA members are on good broadband links where 200 MB per talk isn’t an issue. Personally I reckon we could double the file size without any problems.
Thoughts?
I also can’t provide a definite answer, but I suspect the answer to both questions is “not really”.
The Julian Day system’s great strength is that makes it really easy to calculate the time interval between two dates/times, which is difficult in most calendars. But unless they’re assembling historical chronologies, or doing astronomy over long periods, how many people actually do much date arithmetic?
The system’s weakness is that its epoch was nearly 7000 years ago, so Julian dates are big numbers. In the past, scribes got lots of practice at writing out big numbers that start 24…. But nowadays it leads to loss of precision in computer programs. Computers typically do calculations to 16 significant figure precision. If you waste some of those figures on 245… you have less precision on the digits that come later. A Julian Date stored in a standard-precision variable in a computer program is only stored accurate to 20 microsecond.
Many of the applications today that involve time arithmetic involve computer operating systems where a lot can happen in a microsecond. They usually use Unix times, stored as the numbers of seconds since 1 Jan 1970. That gives you 0.1 microsecond precision. I think pretty much everyone other than astronomers use Unix times rather than Julian Dates nowadays.
So in short, it’s not clear to me many people outside astronomy would have had much use for Scaliger’s system. And it’s not clear his decision to use an epoch in 4713 BC was ever a useful one. Is it fair to suggest today, even astronomers only use the system out of tradition, rather than because it’s good?
Nice work! Out of interest, is that the Astronomik clip filter? I’ve been wonder for a while whether that’s compatible with full-frame DSLRs, since the list of supported cameras doesn’t include the 6D. But it looks like it is!
Cat 5 cable is pretty amazing stuff. It’s built to carry very high data rates with minimal dispersion over long distances, and it works!
I know somebody who wanted to have a PC they could access in their shed and indoors. He wired the keyboard, mouse and SVGA data signals down 30 metres of CAT 5 cable buried under the lawn. Normally SVGA deteriorates even more than USB over long distances, but his set up worked perfectly.
Then again, I think he paid an arm and a leg for the connectors (impedence mismatches can be a nightmare if you bodge the cables together), so probably best to try a simpler solution first.
Roy is right.
5 metres is right at the limit of how far USB signals can travel without dispersion leading to an unacceptable error rate. So you really need to have something on the end of the cable acting as a repeater.
An active USB cable does exactly this: there’s a small repeater in the plug furthest from the computer. I’ve used cables like this and they seem to work.
I imagine that plugging the far end of a passive 5m cable into a powered (or even unpowered) hub would have the same effect, but I’ve not tried it.
As Jeremy says, Data Protection means that the BAA couldn’t do this without getting permission from members. We could potentially have an opt-in members’ directory, but I fear a lot of our members would be very uncomfortable about putting their addresses in the public domain — especially those with very expensive telescopes in their back gardens!
I am keen to develop the BAA website into a more social platform where are members can share images and send messages each other. Perhaps it would be worth giving members the option of specifying a home town that we could plot on a map…
OK – Yes, I think it was those images I was thinking of. It was something I saw scroll past on twitter a couple of months ago, so I can’t go back and check!
I suppose the selling point of a Goto system for me is that I’m often giving people tours of the sky, and you’ve usually only got half an hour before they get bored/cold, so a Goto system lets me show far more objects in that time than if I was finding them manually. Perhaps I’m just slow at star hopping…
What really annoys me about Goto is not being able to declutch and yank the telescope around without losing alignment. I’m quite tempted by the SkyWatcher FreedomFind thing which solves that by putting encoders on both axes. But I think the cheapest FreedomFind mounts are about £950, and at that price it’s not exactly top of my wish list…
