jambouk

Thanks all. Guiding isn't an option, and he isn't after Astronomy Picture of the Day, and a bit of eggy stars at the edges won't be an issue. I've just found this thread which shows some nice results with 60 seconds unguided subs (4.5 hours) with a C11 HD at f/7 and a 294MC.: https://forums.sharpcap.co.uk/viewtopic.php?t=1969 I think he would be happy with something 50% as good as this. James

A friend at my local Society has asked me for some advice on what camera he should get. He has recently got a standard C11. He doesn't want to guide and can reliably get 30-second exposures with his DSLR on his old driven equatorial mount. He is primarily interested in DSOs, but would like the option to capture planetary/lunar data too. He wants to capture more Ha than his old unmodified DSLR allows, and is keen to get a one-shot colour camera. He lives under a fairly dark UK sky. Now I presume a cooled camera will still be best, even for 30-second exposures, but which one? Budget under £1000. Thanks for any replies. James

We all talk about the importance of not looking over a neighbour's roof as the heat loss from the roof / chimney will disturb the seeing , but is there any research out there to prove or disprove this? Thanks.

With so much information for amateurs available on the internet now at the touch of a button or swipe on a smart device, including the resources and voices on SLG, is there a future for Journals and magazine, either printed or in electronic form? The BAA have set up a survey to seek opinions from everyone on this (members or the BAA or not), and about the BAA Journal. There is also a copy of the BAA Journal if you've not seen it before. Survey: http://bit.ly/41Uxy5z Sample copy of BAA Journal: https://britastro.org/wp-content/uploads/2023/06/JBAA_2022August.pdf

Not all of the nuts and bolts are stainless so rust will form.

Whilst researching for a talk for my local society I've gone down a rabbit hole about precession and the ecliptic. But I need some help to solve a problem. I get lunisolar precession, where the Earth wobbles around the axis of the ecliptic by 23.4 degrees over 26,000 years or so. I also get that there is obliquity, where the wobble around the axis of the ecliptic varies between 22 degrees and 24.5 degrees over about 40,000 years. But what I am trying to work out, is why the Earth's ecliptic varies overtime. The graph below suggests it varies on a cycle of 71,400 years or so, and its maximal change is about 4 degrees. I know there is planetary precession, the orbit of the Earth around the Sun along the ecliptic being distorted by other solar system bodies, but the value for this is quoted as 1.2 degrees, maybe 2.4 degrees as the vertex angle, which is still some way off the 4 degrees from this plot reportedly produced by Jean Meeus (https://commons.wikimedia.org/wiki/File:Earth's_orbit_-_Variation_of_inclination_en.png#file). I thought this paper had the answer, but I can't see it unless I'm missing the wood for the trees: https://www.researchgate.net/publication/250008115_Physical_backgrounds_of_Earth's_rotation_revision_of_the_terminology Any ideas what causes the 4 degree variation in the ecliptic over a 71,4000 year cycle? Thanks. James

A lovely find, well done. Looking online, I think it is likely this publication: https://www.worldcat.org/title/491333973 And there is only one copy I can see available online to buy, so probably moderately rare. Moon Landing fanatics would likely be interested in it. https://www.abebooks.co.uk/servlet/BookDetailsPL?bi=20154327309&cm_sp=det-_-bsk-_-bdp James

Thanks, I'll give that a go. I want both the comet and the stars to be sharp, hence using DSS to stack both, using the third stacking option "Stars and Comet". There is not enough detail in one sub to show the comet, and I don't like the streaky stars if just stacking on the comet.

Thank you. Do I need to apply this to the lights, the flats or the darks? Do I use Kapp[a-Sigmal clipping or Median Kappa-Sigma clipping? When opting for either of these two, I can change the values for "Kappa:" and for "Number of iterations:" - the default setting is 2 for Kappa and 5 for iterations. What values should I try? Dropping Kappt to 1 or increasing to 3 seem to make no difference. I've not altered iterations yet. What is the range I can potentially opt for?

The attached image has been grossly stretched to show the issue I am encountering. The background stars have streaks when stacking in DSS to get both stars and comet sharp. The comet drifts from top to bottom in my subs from the first to last sub, and as polar alignment wasn't perfect, the stars drift slightly left to right between first and last sub. I presume the streaks are the tracks of the stars in relation to the comet's path, but is there a way to reduce the streaks in DSS? Would better darks, better flats help, or even better lights? Or is there a setting I can use to reduce the impact the streaks have? Grateful for any advice to rectify this data, or when imaging a comet in the future. James P.S. I think the banding left to right in the bottom third of the sub is from my flats.

OK. For the planetary equation, this is using focal ratio, not focal length. Two telescopes with the same focal ratio, but different focal lengths (and hence appertures) will presumably not be equal? I'm also not sure how one identified the optimum sampling rate (I presume sampling is being measured in arcseconds per pixel) from this equation. For DSO imaging, if one doesn't know the expected FWHM as this is the first camera to be used, what value would one use? What is bog standard average UK seeing? Thanks. James

Vlaiv, what tool do you recommend people would use?

Does this illustrative tool have any role today in determining what camera to match with what telescope? Or does the move to CMOS sensors with generally very small pixels and shorter exposures negate the need to worry about matching kit any more?

I've seen a drawing of the Orion Nebula by Messier and also the Andromeda Galaxy, but did he draw other nuisances in the night sky in his hunt for comets? Thanks. James

Ah! Yes, you are correct. The version I've been using ends with the bibliography and now I can see that pages have been removed. My other set have the index. I did often wonder why such a great tome didn't have an index... Thanks. Mystery solved. James

Has anyone has ever created an index to the three volumes of Burnham's Celestial handbooks? James

I’d say this is pretty good for an unguided 52 minute exposure. You could try tightening up the PA, but guiding should smooth this out, unless you are planning 30 minute subs or the like.

With a basic refractor, how is the focal length measured? In optics, the focal length if the distance from the lens axis to the principal focus as shown in the diagram below by the grey line. But reading online, people talk about measuring the focal length by pointing a refractor at the Moon and moving card at the back to bring the Moon into focus, and then measure the distance from the objective lens to the card... This would be a very different value to the former method. Which is correct? Thanks. James

Thanks

With a double stacked 50mm Lunt and a B600 blocking filter, are there any advantages for imaging [or observing] of using a B1200 blocking filter?

I got one of these for £99 and I have to say I am mightily impressed. The site is always breezy and I think on the whole on calmer days it probably produces produces 25W (rated at 500W) but I have recorded it doing over 200W in a stronger wind. It certainly keeps the batteries charged. I suspect in a sheltered location it would be next to useless.

Just found this plot which seems logical though no idea f it’s validity / authenticity: https://electronics.stackexchange.com/questions/125220/lead-acid-max-discharge-rate

Yes, I get the same error code when trying the link in the original post. There is a scan of the equipment they built for the Stockholm Observatory on archive.com https://archive.org/details/40-ft.RevolvingDomeForStockholmObservatory/mode/2up I have a couple of copies of their catalogues which I keep meaning to scan and put on archive.com Ian Glass in South Africa I think is also interested in Grubb Parsons, I communicated with him in 2016 about them.

As above. The altitude adjustment system is much better with the AZEQ6, and encoders are good. I think if you are used to an EQ mount you are unlikely to ever use it in AZ mode. If you wanted that small refractor then go for the AZEQ6. If you don’t actually want it, and £400 is a lot of extra money, go for the cheaper option. But the AZEQ6 is lovely. Though if they are itching to get rid of them, one has to ask why? Is something new coming to replace it? James

Ok. There is nothing wrong with it, but my mate who is an electrical engineer wanted to study it. James