[Dr Paul Leyland]

Hmm, you posted while I was still composing my reply so I didn’t see your annotation.

Either or both of us could be wrong.  We can’t both be right.

Paul

[Dr Paul Leyland]

Can you post your image here or on your member page?  We may be able to help with the identification.

[Dr Paul Leyland]

Unfortunately, I see no image with Chromium on a Ubuntu system. Looks like the web site not be as portable as desired 8-(

This is what the HTML looks like which, incidentally, gives the URL of the image:

This is how it looked in the guider 2019-12-01T17:18:12 3 hours after the discovery was announced (South is up)

Nothing obviously wrong so perhaps it’s in the CSS?

[Dr Paul Leyland]

Unfortunately, I see no image with Chromium on a Ubuntu system.

Looks like the web site not be as portable as desired.  8-(

[Dr Paul Leyland]

“I find it much easier not having to mentally convert black dots on a white background to bright dots on a dark background”.

I almost always display negative images for comparison with (in my case) VS finder charts. A single simple mouse click.

[Dr Paul Leyland]

I don’t have this one, but I do have the full 17-volume Tycho & Hipparcos catalogue which I picked up 2nd hand for £250.

The relevance is that volumes 14-16 are essentially the MSA, though printed at a slightly smaller scale. A superb atlas.

Incidentally, if you are going for Uranometria 2000, get Vol 2 as well.  Otherwise you will be restricted to the northern hemisphere.  Even up in sub-arctic Britain quite a bit of the southern sky is visible.  I wish I had realised that when I bought only V1 and now regret the decision to save money.

Added in edit: just bought a “like-new” copy of U2000-V2.  Thanks for prompting me!

[Dr Paul Leyland]

No need to stick with your copy except for sentimental reasons.  Second-hand copies are dirt cheap.  I’ve five different editions in the library, none of which cost me more than a few pounds.  The first (1910) edition was was given to me by a friend whose astronomer father had died recently.  It’s been well-used for the last century and ought to be re-bound professionally.

If you wish I can put you in contact with a guy who is down-sizing his library and from whom I bought the Tycho catalogue.  He had a copy of Hans Vehrenberg’s “Photographischer Stern-Atlas” which goes down to mag 14 or so.  Don’t know whether it is still for sale.

[Dr Paul Leyland]

Seconded!  A superb atlas.  I used it on the last session at the telescope.

[Dr Paul Leyland]

Go for it.  On Twitter too.

[Dr Paul Leyland]

Thank you.  I’ve been using APT in batch mode to process many thousands of images from high-cadence photometry runs, at least in part because it is so easy to automate compared with AIJ.  Time for me to re-evaluate that decision.

Now to see whether your macro works in LibreOffice.  The ones supplied by the BAA-VSS do not, another reason why APT has been the utility of choice.

Paul

[Dr Paul Leyland]

With the red laser I suspect it’s thermal expansion of the cavity which changes the resonant frequency.  The LED is a broadband emitter but constructive interference occurs only when the cavity is an integral number of wavelengths.  Change the length and the resonant wavelength changes.

The Nd transition is at a frequency governed by an electronic transition involving a 4f orbital.  Those orbitals are largely isolated from their chemical and thermal surroundings so the transition is very much narrow band which doesn’t change greatly with temperature.  The pumping diode is a broadband source but that doesn’t matter as long as it emits strongly enough at the laser frequency.

In a previous life I used to play with a tunable laser — a dye laser pumped by a fixed frequency argon-ion laser in that instance. It was tuned by changing the length of the cavity.

[Dr Paul Leyland]

Clouded out.  8-(

[Dr Paul Leyland]

When I first saw your post I thought that 500mm was the aperture, not the focal length!

[Dr Paul Leyland]

I’m trying to orientate myself.  To make things easier, could you say (a) whether shorter wavelengths are to the left or the right of the image as shown here and (b) are the lighter colours bright emission lines (i.e. it’s a positive image) or dark absorption lines on a negative continuum?

I’m almost certain that its the first in case (b) but it would be good to have it from the horse’s mouth as it were.

[Dr Paul Leyland]

I can see a few images of Landolt fields being taken when I’m next back in La Palma.  Let’s see, I’ve RGB&Luminance filters, pretty pictures for the taking of (and which I’ve used precisely once, on M57, just to see whether they work); Johnson-V which is by far the most used for VS work; Sloan g, r and i (only ever used the second for production work, though i was once used as an experiment to see whether it improved contrast of Jovian surface features).  A “H-alpha + continuum” is in there too, but it’s never been used because I’m not interested in either visual work or in taking pretty pictures of H-II regions.  Two slots are empty — one will remain that way and I’m tempted to get a Star Analyser SA200 to play with.

Any suggestions as to what other photometric filters may be worth purchasing, possibly part-funded by selling off the ones I don’t use?

[Dr Paul Leyland]

That is also my belief.  Unfiltered magnitudes also correlate very well indeed with Gaia-G magnitudes.  This should come as no great surprise …

That’s why I generally quote Gaia-G magnitudes for objects on unfiltered images I’ve taken.  Please note, these are NOT images taken for photometric analysis, for which I almost always use V or Sloan r filters.

[Dr Paul Leyland]

Further to Jeremy’s comment: the use of dark and flat frames goes a long way to to cleaning your image of truly hot and cold pixels.  However, it cannot deal with either cosmic ray hits or satellite trails close to the VS or a comparison.  If you see any anomalously faint or bright estimate, take a close look at the corresponding image to see if there is an obvious reason to reject it.

In my case, I throw away perhaps two estimates per thousand.  It’s only when processing thousands of images does it become really noticeable.

[Dr Paul Leyland]

Thanks.  That’s where I just found it but I’m quite certain that it wasn’t there when I posted yesterday — it was the first place I looked, not least because that was the destination of the link in the email sent to me.

The forum page also now shows the Oct 2019 issue; it did not yeterday.

Oh well, it all worked out in the end.

[Dr Paul Leyland]

8<-------------------------------------------------------------------------------------------->8
On Tue, 2019-10-08 at 21:21 +0000, BAA electronic bulletins wrote:

The BAA’s latest newsletter
View this email in your browser

BAA October Journal now available on line

How quickly the longer chillier evenings have come around. It seems
…
course, after the July eclipse, which many BAA members viewed, Nick
James personal account makes good reading. He is still collecting
eclipse images and videos for the BAA Eclipse 2019 DVD. If you would
like your images to be included please send them directly to
solareclipse@britastro.org
8<-------------------------------------------------------------------------------------------->8

The first bit specifically states that the October Journal is available on line. The second quoted portion only makes sense if it refers to the 2019 issue.

I still can’t find the October 2019 issue anywhere 8-(

[Dr Paul Leyland]

Despite the mail announcing its availability I’ve been unable to download it.  I contact the Reply-To: address to ask for assistance.

Paul

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