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Good!
Sounds promising.
Note that a luminance filter removes the near-IR which, if present, gives an unusual colour balance. You are (or should be) not interested in what it looks like but only how many photons you have available. My advice is to run unfiltered in future and let the IR photons through so that they may contribute to the overall signal.
<p class=”wp-dark-mode-bg-image”>I took a calibrated 2 min sub, debayered and extracted the green channel (OSC camera).
Something worth remembering: if all you are interested in is the change of brightness as time passes, it matters relatively little what filter(s) you are using.
If you extract all four Bayer layers (1xR, 2xG and 1xB) and then add them together you will have more signal and relatively less detector noise in both star and sky. If all channels have equal signal, which they won’t, the SNR will be increased by a factor of sqrt(2) or approximately 1.4 which is well worth having.
<p class=”wp-dark-mode-bg-image”>Right so I was woken at 3am by the youngest sprog and couldn’t get back to sleep, so I did a load of internet searching and reading around SNR, AstroImageJ and aperture photometry (totally normal behaviour, right?).
<p class=”wp-dark-mode-bg-image”>Stumbled across this useful looking calculator…<br class=”wp-dark-mode-bg-image”>
https://mirametrics.com/sn_calculator_mvn.php<p class=”wp-dark-mode-bg-image”>Plugging in the pertinent data, or estimates of, and it thinks using a 102mm refractor operating with 2 minute exposures, and assuming my minimum acceptable SNR to be 500, then it looks like I should be aiming for stars of at least mag 12.5 with a 2% transit depth.
<p class=”wp-dark-mode-bg-image”>Edit: Plugging in numbers for my 300mm/1500mm Newtonian says it should be good down to mag 14 ish with a 2% depth.
Perfectly normal behaviour, IME.
Your numbers sound about right to me and consistent, though not identical, with what I posted earlier.
Your noise will depend greatly on your sky brightness, of course. Don’t expect as good results from a brilliantly moonlit Bortle-7 location as a new moon B4.
I would recommend installing a proper photometry package (I use and recommend APT, Aperture Photometry Tool) but there are several others available. Any of them will give a good measurement of the SNR of any given star in any given image.
Incidentally, and this doesn’t apply to exoplanetary transit work, stacking many unsaturated images in addition mode will increase the SNR by a factor of the square root of the number of images. By adding the images you preserve the photometric accuracy and let the counts per pixel exceed the detector’s saturation limit.
Craig: that FOV is comparable to my 400mm, which is 16.45 * 13.18 arcmin, or 0.27 x 0.22 degrees. I have not yet had any problem finding a suitable comparison star but, to be fair, stars do become much more common at fainter magnitudes.
Once more: suck it and see is my recommended approach. Remember that you can do all this sort of experimentation at your convenience – you do not need to wait until a transit is imminent. If you do so for all the stars which you are likely to observe over the next few weeks you can choose which telescope to use as appropriate.
Gary: I don’t understand.
I remain logged in for days or weeks at a time. Perhaps we use different browsers: Firefox under Ubuntu here.
I have no personal experience with a 102mm aperture but my 400mm can do useful work on a 1% depth at 13th-14th magnitude. Simple scaling says that you have 1/16 the collecting area, which corresponds to three magnitudes in brightness.
Accordingly, I expect that you may have a chance with HAT-P-20 but it’s not certain. Certainly well worth giving it a try.
Regardless, it’s easy enough to test the capabilities of your equipment. Choose a star of a particular magnitude and see how long an exposure is require to reach a SNR of at least 500 and preferably 1000. If it is a couple of minutes or less, and preferably less, you can measure a transit of depth 2% or better. Repeat with fainter stars until you determine your limiting magnitude.
Good luck!
Paul
SWarp (https://www.astromatic.net/software/swarp/) is the only stacking program I use most. It works exceedingly well.
I believe that SWarp is available for the Mac. (I have never needed to look for it before but here it is: https://ports.macports.org/port/swarp/ )
I use a local installation of astrometry.net to put the WCS on my images. Toddle over to https://astrometry.net/ for links to both the on-line plate solver (“use”) and how to drive the local installation (“download”). I already knew that a MacOS version of the local installation exists.
FWIW, I use “ANSVR” to put a WCS on images taken with Maxim DL under Windoze for the purpose of a rough and ready indication of the centre of teh field for synchronizing the mount’s idea of its pointing location to the telescope position. Never tried stacking with SWarp under that OS but often use Maxim DL’s stacker to see when enough subs have been taken to give a good enough SNR for photometry. AN and SWarp are used subsequently to do a proper job.
I would love to have them but La Palma is even further for collection from Falkirk than is Cambridge.
Let’s hope you find a good home for them.
As of two hours ago:
Knud Jahnke @knudjahnke.bsky.social
The closest edge of the fire perimeter is currently 500m from JPL. But wind speeds have decreased and wind is not blowing towards JPL anymore.
https://www.fire.ca.gov/incidents/2025/1/7/eaton-fire
in response to my post on Bluesky yesterday.
The Danish book looks fascinating.
I collect old astronomy books and I can just about read North Germanic (Danish, Swedish, Norwegian, Icelandic).
After a bit of research: https://openlibrary.org/works/OL38809658W/Populaer_astronomi
Also interested in your QCD book on Amazon. I’ll contact you directly.
Yeah, wooden roll off seem less dew laden.
…
I will also start assembling the RPi bits for a longer term project.Good to know about the RoR. One is under construction at Tacande, not that dew has been an issued there. (The scope has a dew heater band around the optical window but I have never used it.) My RoR has a steel frame holding white foam-filled plastic panels for their thermal properties.
Also collecting bits and pieces. I’ve a tatty old 250mm Meade, a camera with integrated filter wheel, OAG and Lodestar, RPi and Odroid SBCs so far but will need quite a bit more yet, including a UPS, WiFi access point and various bits of software.
When complete (late 2025 or spring 2026) it will be drivable over the interweb thingy. I will likely ask BAA members to act as alpha and beta testers in return for free imaging/photometry/astrometry of objects of their choice. No spectroscopy for some significant time, if ever.
Interesting.
However, CHL alone submitted over 12 thousand observations of MAXI J1820+070 in 2018. I suspect it will be readily noticeable in the all-time lists.
It may be interesting to do the same for the VS and the spectra databases. I would expect SS Cyg and MAXI J1820+070 to be among the brightest sources in the VS sky.
Nice maps.
Pretty obvious that many people like to image M31, M42 and M45. They really do glow brightly in the all-time map.
Hopeless here in the UK (Jan, Apr-Jul, Oct-Dec) and poorer than usual in La Palma (Jan-Apr, Jul-Oct). Water clouds in the UK; dust clouds and high winds in LP. Some months were split over two locations but something like 24 weeks were spent in LP and 28 in the UK.
Still managed to do some useful photometry of VS and asteroids though.
I did a quick calculation based on Betelgeuse subtending an effective 2 arcminutes through a minimal sized pupil, a lens which is likely defocused and has significant aberrations, mechanically scanned over an extended area of retina.
It appeared to show that one would certainly not want to stare at the SN but glances would cause no significant damage beyond very short lived after-images.
Impressive. There are several there which I would love to own, having only reproductions so far. Principia and Mechanism of the Heavens, in particular.
Somerville’s work is still well worth studying despite having been published just shy of 200 years ago.
Nick: I’m on your side. However, in my opinion it will be a courageous decision to be made and on a par with the recent re-definition of what constitutes a planet.
As space is short in the page limited Handbook, could thought be given to removing pages 117 and 118? Surely its pretty much unchanging from year to year and readily Googled? I think I used the pendulum equation once as a teenager.
Similarly, as a space saving/creating measure, could the line spacing on page 116 be changed? That might free up ~1/3rd page that could be used for some small item like expected dates of observable Earth flyby/gravity assists.
I also wonder who looks at the Bright Stars info page. Genuine question: who uses it?
BTW none of this should be taken as criticism. A huge amount of work must go into creating the Handbook and I for one am very grateful to those who put in the hours. As a result of their work I’ve already started to plan my 2025 observing year. Its good to see the Handbook evolving. Thanks to all involved!
You’re a better man than I, Gunga Din.
I also think that we could consider pruning some of the present material but didn’t mention it for fear of the likely backlash and argumentation over what could be removed and what must be kept.
I have never, ever, used the bright stars information. Similarly for those pages mentioned.
+1 for Earth fly-by and gravity assists.
Nick: undoubtedly so.
To be honest, I had never noticed but then, I’m not a planetary astronomer.
I foresee a very vigorous, not to say rancorous, debate over whether J2000 is kept in perpetuity or whether we move to J2050 within this decade.
Closely related: proper motion already affects my code which attempts to match Gaia data to historical positions. A surprisingly large number of stars have moved more than 2″ since 1950. One day I really must download the PM data too and do the job properly.
