Malpi12

Thanks, yes I tried that but but never got it to work, even giving it an accurate, rather than approx. location, - still "unsolved" so either it does not like my non-round stars or I am doing something stupid ! I think I got the cats. downloaded, but perhaps not correctly ! I'll try again with some nice bright stars and shorter exp. , , Meanwhile, any chance someone with a dslr, and meter +/- ASTAP. could try the 50% histo method

This site is interesting https://pbase.com/samirkharusi/image/37608572&exif=Y Briefly : he derives m/sq thingy by the length of exp needed to get the histogram (in a jpg not a raw) to 50%. He says the method was calibrated at a dark site but the calibrating device is not specified (or I missed it !) I wonder if anyone with a sky quality meter has evaluated this or similar camera type measures? Reason for my interest : Until now I have relied upon Mk1 eyeball to know how good the night is. However it seems a long time since I saw, unaided, the Andromeda Galaxy or the Rift in the Milky Way. Is it my old eyes or global warming ?! Also, after playing with fixed cameras on a tripod, my thoughts are turning to a tracking device and sub lengths.

I remember some time ago reading discussions about the possibility of seeing (visible spectrum !) a GRB with amateur equipment, I thought that I remembered magnitude 9 as being a reasonable estimate, so I googled to refresh my brain-cell and was astonished to find this :-- GRB 080319B was a gamma-ray burst .... 06:12 UTC on March 19, 2008. ....a peak visual apparent magnitude of 5.7 and remained visible to human eyes for approximately 30 second.... From https://en.wikipedia.org/wiki/GRB_080319B

Things to do when it is cloudy/raining outside - ponder upon the little bit of data one already has Are you sitting comfortably :- More reading about this phase folding lark : the period does not need to be known in advance, it will produce a smooth plot with guesses near the correct interval, and a scattered plot at other guesses, more about that lower down. First we look at the linear time plot,, , Even with the very limited data that I have so far I think we can have a guess at an approx. period. (hindsight is a helpful thing as well ) It looks like my first obs. (27 Aug) was near a min, then three more, near days 15-19, 24-25 and 33-34 (pink) The first long, cloudy, interval is about twice as long as the following two, so assume that there were at least 4 minima in this 33 to 34 day period - the red line with an uncertain start point but a fairly well defined end between day 33 to 34. I say 'at least', but there could have been eight or 16 ! However there is no indication of a missed minimum during the reasonably filled last period. So, a best guess of between 8 (=32 days) and 9 days (=36 days) for the red seems reasonable ??? It turns out that I need not have learned spreadsheets, my fav. Gnuplot also has a Modulo function., which makes it easy to generate many phase plots with guesses at the folding period I first chose 8, 8.2, 8.4, 8.6, 8.8 and 9 days. and Lo! the plots magically come together best at a 8.4 day period, how satisfyingly close to an actual 8.38 that is , , , or have I just introduced some severe observer bias with afore-knowledge I show a multiplot but can upload individual larger ones if anyone wants them. Trying to narrow it down with 8.35, 8.4, 8.45 etc. plots was less convincing - more data needed - I wish!

Using my Canon 60d to observe the variation of U Sagitta (an Algol type eclipsing binary) was quite interesting https://stargazerslounge.com/topic/398978-u-sge/ but so far I have only caught it going in to minimum, not out the other side ! Trying to time minima with British weather I have decided is a mug's game ! ! I found, in Burnham's Celestial Handbook, S Sagitta, a continuosly varying candidate nearby. Much more convenient for occasional viewing between clouds. Bright and a good 1 magnitude range. A month of obs later I had this not very smooth set: However, with a hint by @IB20 and @robin_astro in https://stargazerslounge.com/topic/395015-algol-variables/?do=findComment&comment=4277498 I delved into the rabbit hole of Phase Folding, learned how to code it in LibreOffice, and produced this quite interesting phase diagram. A wiki page https://en.wikipedia.org/wiki/S_Sagittae on S Sag has a plot which, when resized and overlaid in Gimp, is a nice (I think !) match. Some brief details of my home-brew method (a full description would be a bit tldr!) images were variously stacks of 10 to 25 subs in DSS, camera fixed on tripod, vintage lens 135mm @ f2.8, exp 2sec, 800iso magnitudes estimated in Gimp using a 10x10pixel aperture in histogram mean, then in Gnuplot I fitted the data with a 1/x^2 curve to match the aavso comparison stars between m3.8 and m7.8.

Slide 5 is the answer ! " using 5second exposures lOOmm lens (58mm aperture) down to 8 magnitude 200mm lens (72mm aperture) down to 10 magnitude " The clue is "aperture". yup! that makes sense From Wiki n=f/d for things far away or in my case d=f/n d=28/2.8=10mm d=50/1.8=28 d=135/2.8=48 So yes, as you said, I should stay with the 135. Thanks.

A bit later, and the poor S/N is evident down in the minimum described in https://stargazerslounge.com/topic/398978-u-sge- 3rd post down

my first go at an Eclipsing Binary, Data from night of25/26 Aug Using a DSLR camera (60d) with a 135mm lens on a fixed tripod. I didn't know what to expect so I collected bursts of 25 exposures ( each 2sec at f 2.8 iso800 ) at intervals from about 11pm through to about 3am when trees stoped play ! to speed processing time and for a first look, I choose samples of 5 subs at suitable intervals from the whole set. In Gimp I used the histogram-mean tool (with a rectangle selection of small size to just encompass the stars without too much background noise) to measure each star and plotted the results in Gnuplot. I was surprised at the sharpness of the entry into the long minimum phase of the eclipse. Gnuplot has a crafty tool to enable a 'best fit' of a polynomial function to a set of data. I have chosen a 2nd order quad g(x) for the fade and a constant f(x) to fit the min. data. EDIT : the x-axis is in decimal hours, local midnight bst is at '2' hours, the y-axis is in AAVSO style magnitude (m x 10 ) so eg. 80 is m8.0.

Thanks @andrew s and @JeremyS A very interesting PPT presentation, lots to think about. Yes, the faint limit was beginning to be my worry, magnitude 9 or thereabouts was starting to be a problem in my (early) experiments with U Sge. I'll post my results so far with that one in a bit !

, , or should the title be Photometry of variable , , My setup : a camera with lens on a fixed tripod (pan & tilt, no tracking) Should I use (A) 135mm (telephoto-) lens to get "close in" or (B) a shorter lens, perhaps a 28mm wide-field ? I have been doing A, but that allows only short exp. of 1 or 2 sec to avoid too much trailing. Now, over a cup of coffee I got to thinking (! an unusual thing I know ) With A all the precious photons get spread over many pixels whereas B they get concentrated on fewer ? 135 and 28 have f=2.8 or a 50mm f=1.8 , all are vintage (1960s) M42 with poor to horrid star shapes ! Camera is a Canon 60d (lots of small pixels ??)

Deleted. Erroneous prediction !

I mentioned in @IB20 's Algol topic that U Sge looked like an interesting target with a sharp swift eclipse might fit into an evening/night viewing. I was mistaken ! :- With Stellarium helping and a few tripod shots with Canon 60D + 28 & 135 vintage lenses I found my target at about mag 6.5 a few nights ago. So far so good, then the task of extrapolating the one recent AAVSO obs on 29July. Using a period of about 3.38d x8 brought me to yesterday evening. Just as I had completed my back of envelope calculations 11pm, I found there was clear dark sky and Lo! a few more quick shots revealed it down at 7.5m already ! I followed until 3am (when it went out of view in trees) at about 8.5m ( EDIT actally on closer inspect about 9.09 ! see later post ) or thereabouts, I still have not processed all the images, Such a long duration minimum (on closer inspection zooming the avsso obs confirms it) surprised me and implies a much larger dark companion, in proportion, than in the case of sharp Algol. I am surprised that it has not got more obs on aavso given its prominent position in northern skies,what am I missing ? Nicely placed near M72 [ediit: M71 init doh!] and the The Coathanger, always nice to see.

Very nicely done @IB20 , very interesting. Have you found a new one yet? From @JeremyS's link this one (sort of a bit below and left of Lyra) in Sagitta looks interesting for bino (or in my case dslr on tripod because my eyes are very old !) U_Sge, Max, m6.5 Min2 m6.7 Min1 m9.3 Period, 3.38d Dur, 14h a swift sharp fall to min1, and a rapid interval should give us a chance between storms !

I am sure you meant only some of them, the others of us who fondly remember Fred Hoyle will have a big smile

Do you know if I can I do that somewhere in DSS as well ? I did try Siril some time ago but it made my brain hurt and fall off its step learning curve thanks.

Hi, I am still trying to get my head round the Imgur page (it is asking me to take more cookies and whitelist my adblocker ! (neither of which I wish to do on this browser ) However a quick look and I have got your settings image off it (dont you just hate message boxes in programs that dont let one copy/paste !) and examined in IrfanView, see lower down :- Firstly - I am still a beginner imager with a 60D (astromod) which is similar to the 600d and, after a steep learning curve with DSS, a long time ago, I do get colour ! I was surprised to see "Gray 16 bit " Ah ! I thought !! but it tuned out to be a red-herring and mine also says that ha ! so I have learned something thanks So then I compared your settings (on the right below) with mine which (after I removed my bias frames and allowing that I am using Kappa-Sigma clip) looked similar to yours except for the Red Arrowed bits. I wonder if that may be a cause ?

VLC is very good but a bit of a steep learning curve, which my old brain needs to relearn each time I need to use it ! An alternative for MOV to AVI is VirtualDub, which is also freeware. ( It can do lots of other things as well, like brightness/contrast/crop and more plugin effects ) Interesting, I didnt know it did jpeg, that explains why the files are so much bigger when converted to AVI ! I wonder if Canon is limited to only MOV !?

Good luck with your new modified journey . I got my first modded cam earlier this year and finding it very interesting. Coming to a good season now, with lots of good autumn Ha targets.

Juan = https://www.cheapastrophotography.com

Yes, very irritating. Buy cheap reading glasses from the £1shop (actually £1.50 !) Remove one lens from the glasses for your scope looking eye. Use the remaining lens side for your reading eye. Works a treat for me. For the future, to do job : add a flip-down dark patch to preserve the dark side (to save having to remember which eye to close 🤣 ! )

Thanks for the headsup, It is (c) a pic of "our" black hole SgrA* Link to the EHT site https://eventhorizontelescope.org/ and it also features on BBC science at https://www.bbc.co.uk/news/science-environment-61412463

and 50y on we are still trying to imagine it Or Lovely Rita Meter Meade " Lovely Rita meter maid Nothing can come between us When it gets dark I tow your heart away " ....

It is good for star-fields and small nebulosity but wipes out wide nebulosity which it thinks is background ! I like it, good rescue

some further messing in Gimp for you to try :- construct an artificial flat, Duplicate the image to a new layer then with with Filters > Blur > Gaussian Blur choose a size in both X and Y which is a large fraction of your image pixel dimensions Change its Layer Mode to Subtract then merge down. Here is a quick first attempt to illustrate possibilities (it is a bit heavy handed !) using size 500 in both X and Y I have cropped the margins as this method creates edge artifacts where the blur runs out of ststistics. happy gimping ,,,Im no expert, give it a whirl,,,

Good point ! In my previous posts I said "delay between exposures" >> To avoid confusion I should have said "interval between exposures" They say a picture is worth a thousand words!, does this help. My wired (if anyine wants pics of a wireless one let me know) 'ometer set for a start-up delay of 4sec. 3 bulb exposures of 15sec each and a write-enable-delay-interval-wait of 5sec.