Xilman

2 minutes ago, Rodd said:

My point is Sirius B is brighter not sky glow.  I thought that would be obvious.  Have to switch gears a bit and be maleable.  In this example Sirius A is the "sky glow" that is interfering with Sirius B.  Show me an image taken with a 4" scope that does not make use of a special filter or diaphram bloacking mechanism.  Just straight imaging on a sensor of Sirius B.

I do not have a 4" scope and so am unable to satisfy your request. Perhaps others here could do so.

15 minutes ago, Rodd said:

Not too convincing--looks like the other blobs in teh image

So?

Exactly the same is true of the blobs in the other image.

That particular blob is within an arcsecond of the predicted position and is within 0.2 magnitudes of the predicted brightness. No other objects are visible within that range on other images which go to comparable depth and no known asteroids are anywhere near that position at that time.

Convinces most people.

2 minutes ago, Rodd said:

That is not an extended target and its inverted.  Not too convincing if flipped I'd wager (as an image--scientifically its fine.  But that is not what I do)-but it is not an extended target.  That is why I said IFN.

Here is the flipped image. As you should expect, it shows exactly the same as the black-on-white version.

17 minutes ago, Rodd said:

 

This is why it is impossible to image Sirius B with a 4" scope (or any scope some times depending on position).  Sirius A is just too bright.  It drowns out Sirius B.

Sirius B is vastly brighter than the sky.

It is most certainly possible to image the Pup with a 4" scope. You need to deal with scattered light from seeing and instrumental distortions, not sky glow. The standard approaches are to use Lucky imaging, possibly in conjunction with a coronograph and/or a diffraction grating to place the companion between the diffraction spikes.

4 minutes ago, Rodd said:

Show me an image of vaint IFN captured from Bortle 8 with broad band filters (no LP filters or other tricks).  Or, maybe there are targets even fainter than IFN.  Bortle 8 and an image of....can't think of one (I haven't imaged it!)

Here is an image of Caliban, also known as Uranus XVI, I took a while back. It was at magnitude 22.2 at the time of capture and was taken in Bortle 4 skies --- approximately 21.0 mag per square arcsecond. The seeing was around 2-3 arcseconds, so the image of the satellite is 4-9 square arcseconds.Let's be particularly generous and assume particularly good seeing --- so only 1.5 magnitudes brighter background per resolution element. The sky background is thus magnitude 19.5, or 2.7 magnitudes brighter than the satellite --- a factor of  20 times. The stacked images accumulated just under 1.5 hours. I could easily have exposed for much longer to get a better SNR but I did not need to do so.

34 minutes ago, Rodd said:

I dont agree with this--if the signal is below the sky fog limit, no amount of doubling will increase signal.  This is only true for dim targets that are below teh sky fog threshold

I disagree.

Let us assume that the signal is 1% of the background and the noise is proportional to sqrt(I), where I is the detector response in photons at each pixel. Suppose for simplicity that all the signal appears in a single pixel and all the surrounding pixels detect only background..

If I = 101 at the position of a signal,, the background is 100 and so the signal is 1.  The noise in the background is 10 and that in the signal-detecting pixel is 10.05.  The signal is swamped by the noise by a factor of 200 and so is indetectable.

If I=1,010, 000 the noise in the signal is sqrt(1010000) = 1005. Subtract the background as estimated from the neighbouring pixels and get the result 10,000 plus/minus RMS (1000+1005).  The noise from the signal is sqrt ((1005^2+1000^2)/2) = 1002.5, giving a signal detection with a SNR of 10000/1002.5 = 9.97.

Detecting objects which are 1000 times fainter than the sky is routine. I've managed it for a factor of 100 without any difficulty whatsoever. I can provide images on request.

All this assumes you know nothing about the signal and its time-dependent behaviour, otherwise you can do much better. If you don't believe me, take a look at measurements of sea-level rises which can be measured to better than 1mm accuracy, despite 10m waves superimposed on 10m high tides.

51 minutes ago, 69boss302 said:

 Tonight is supposed to be a clear night again so maybe Ill shoot this target again sans filter.

Please do, go as deep as is reasonable, and repeat the exercise as often as you can over the next few weeks or months.

It is well within your capabilities not only to record the presence of Cepheid variables but also to monitor their change in brightness and so make your own measurement of the distance to M31.

If you need assistance, please ask. I'm sure a number of people here will be extremely willing to help you to analyse your data. Citizen science in action!

13 minutes ago, Xilman said:

 I have not yet examined it closely enough to see whether you have captured globular clusters, individual stars, and so on.

Now that I have, I can see that you have picked up one of my favourite stars, AE And, bright and clear. It is a blue supergiant in the galaxy.

I now have little doubt that thousands, if not hundreds, of other individual stars in M31 are visible in the full image. A few dozen globular clusters should be there too.

Well done both you! A very nice picture.

16 hours ago, 69boss302 said:

II guess at this point I need to know if I need to change my processing or my capturing. Thank you much for any insight.

Before anyone can answer that question, you need to answer one in return: what are you trying to achieve?

Personally I find that monochrome images can be just as pleasing and as informative as those which are coloured according to the artist's preconception of what they ought to look like.

The version of M31 which appears above is a case in point. It is sharp, detailed and picks out the faint extremities extremely well. That is just an overview. I have not yet examined it closely enough to see whether you have captured globular clusters, individual stars, and so on.

10 hours ago, Gfamily said:

Shared with my Astro Club on their Facebook page. 

Thanks!

And filled in the survey, I hope.

I hope this is the right place; it is the best I can find. Perhaps a mod could move it if needed.

The International Astronomical Union (IAU) is conducting a survey to gauge the level of interest and ability of professional and amateur astronomers to work collaboratively. The survey is open to all astronomers, amateur, professional and corporate.

At the moment the survey is trying to ascertain how many people are willing to help in one or more broadly defined fields: variable stars, solar system, galaxies, data mining, etc. They are also asking about what we've been doing, if anything, within those same areas. The other important question is: how can professionals help amateurs, by running on-line courses, in-person workshops, and so on?

As I understand it, specific requests for help will come specific professional astronomers when and if amateurs are capable of collaboration with them. I expect, but do not know, that future survey(s) will be aimed at establishing levels of interest, expertise, technological capabilities, and so on.

The survey is located at https://www.iau.org/...etail/ann21064/ and I urge everyone to contribute and, further, to pass on this information to others via social media, email contact, and so forth.

I've done my bit. It was very quick, easy and straightforward.

Thanks,

Paul

6 minutes ago, michael8554 said:

Apologies for stating the obvious, but Flats without cooling are okay ?

Michael

You will have the thermal noise in your flats, so either take many more of them and average, or accept noisy science images.

Not a good idea, IMO.

On 26/11/2021 at 12:43, almcl said:

If you can't find a supplier of a ready made one, it might be worth using one of the on-line Bahtinov generator programs to produce a suitably sized one and then submit it to one of the laser cutting services?  I did this some years ago for my 8" and used black acrylic but for 20" perhaps aluminium or even thin steel might be more appropriate.  

Might also be worth cutting one out of cardboard using the generated pattern to make sure it works OK before investing in the real thing?

I made one out of cardboard for my 40cm using a design from one of the on-line resources. It works so well that I haven't spent any money on a more robust version.

I confess: I never thought that I would rule an optical diffraction grating with a craft knife!

1 hour ago, Newforestgimp said:

I will have another round or 3 of collimation, I’m even considering one of those electronic Collimators like the Ocal as I’m just not sure how I would tell if it was any better as it looked pretty good by eye.

I use the Bahtinov Grabber app. Really does make auto-focussing a doddle, not least because it is essentially independent of the seeing. Whether your stars are 2 arcsec or 15 arcsec across (and I have experienced both extremes) really doesn't matter.

With seeing as bad as 10-15 arcsec, about all that can be usefully done is photometry unless you have a very wide FOV ...

1 hour ago, Newforestgimp said:

Thanks Vlaiv,

Im getting a bit tired of the autofocus routines, i thought my eyesight was bad but...

Get a Bahtinov mask. Seriously. It makes focusing a doddle. I also have bad eyesight with myopia and astigmatism and had enormous trouble focusing by eye.

2 hours ago, Newforestgimp said:

Hi All,

Im after a favour, below are a couple of drop box links to two sets of data captured last night, I cant get DSS to stack them, it sees no stars.

I stack differently. First I run the subs through the astrometry.net plate solver. For just a few you could use the on-line facility at nova.astrometry.net but I found it worthwhile to install the software locally.

After the solver has done its job you end up with a FITS file containing a world coordinate system, or WCS. The WCS enables other software to convert between pixel locations and RA/Dec coordinates. In partticular, it allows SWarp to stack images.

Works very well for me but YMMV.

Oh, one thing: best to split 3-colour images into separate files and then stack independently. Re-combine the three or four stacks to regenerate a final colour image.

Others have already comented on your focus and collimation issues.  The astrometry.net solver is remarkably tolerant of such things.

5 hours ago, Zermelo said:

The article says that xenon has previously been used for this purpose, but in that case there is already a trace amount in the earth's atmosphere, unlike iodine.

I would expect trace amounts of iodine to be in the atmosphere for the same reason that chlorine and sodium are present --- sea water.

There is so much Na in the atmosphere that active optics lasers use it to form artificial stars.

No real idea about the relative concentrations of Xe and I in the upper atmosphere and can't comment on whether either or both are significant.

9 minutes ago, saac said:

I'm pretty sure same stood for CO2 100 years ago .   I wasn't actually being serious Xilman  

Jim 

Indeed. Arrhenius did work out the greenhouse effect of CO_2_ over 100 years ago.

20 minutes ago, saac said:

I hope we don't find out ten years down the line that Iodine or any atmospheric compounds it may form are super greenhouse gases  

Jim 

I am pretty sure that the greenhouse effect of any plausible iodine compound is easy to calculate from first principles.

Once more: the amount of iodine used in these systems barely reaches negligible.

I would have thought it exceedingly unlikely to have a noticeable effect because only tiny amounts would be used.

Out in the mesosphere I would expect the main molecule to formed would be HI, as I_2 is more easily photolysed by solar UV. Even, so I would expect much more atomic iodine to be present than HI.

In the lower atmosphere all sorts of molecules, molecular ions and free radicals will be produced. Most of them react vigorously with water and would likely be washed out eventually. I do not have a feeling for what the mean lifetime might be.

Lighter halogens can catalyse dissociation of ozone, hence the recent restrictions on chlorofluorocarbons. Presumable Br and I would do this too but, again, I do not have a feeling for how well they do it.

Anyway, I repeat: only very tiny amounts would be used. In this context a hundred tons of the stuff is only a very tiny amount.

Bahtinov masks for each of  my two main scopes, together with the Bahtinov Grabber app when imaging.

Makes focussing a dream. I used to spend ages fiddling around trying to get the best focus.

This thread arises from Mr Spock's generous encouragement in

Although there are many thousands of variables in the Milky Way which are observed by amateurs and many useful measurements are reported to the likes of the BAA-VSS and AAVSO, very few people monitor variables in other galaxies. I find this rather disappointing.

Amateurs way down south have it easy. Both the LMC and SMC are close enough that a good number of VS are within range of binoculars or small telescopes.

Those of us further north are a little more constrained. Either we use robotic telescopes and/or we look at local group galaxies which rise above our horizon. Note that I am explicitly avoiding supernovae, despite their extremely valuable coverage by the likes of us. The obvious galaxies are M31 in Andromeda and M33 in Triangulum.

I must be honest: visual observers will need large apertures, dark skies, and will be limited to only a few targets.  That said, I have made visual estimates of both AE And and AF And in M31 with a 46cm Dobsonian.

At least one kind of variable, those catalogued as SDOR and are also known as LBVs --- luminous blue variables --- are actually easier to observe outside the MW in some ways. For a start there are more of them and they tend to vary in brightness rather more than the nearby examples.

If you have a camera and at least 20cm aperture there are hundreds, if not dozens,  of  extragalactic variable stars which are within your capabilities and, because they are not monitored as frequently as desirable, are within your ability to conduct genuine scientific research. Even if you don't want to be at the bleeding edge, you could confirm the period-magnitude relationship of Cepheids and so make your own measurement of the distance to M31 and M33.

If anyone would like a challenge, I can very easily provide more help and information .

OBTW, and in line with the double star focus of this sub-forum, I may have discovered an eclipsing binary in M31. More analysis is needed decide whether it is real or not.

On 15/11/2021 at 16:46, Mr Spock said:

Lack of posting - there just isn't enough activity to warrant separate forums. So, everyone, get posting 

Right, you're on. I do quite a bit of VS work and I will try to post more.

Not in this thread, though, as I don't observe Algol or Beta Lyrae, and exoplanetary transits, though double or multiple objects, only have one star.  😉

Any one interested in a thread on extragalactic variables?

For me it is invariably at home, but I have two homes.

In La Palma essentially all observing is instrumental: photometry  of variables stars, asteroids and exoplanetary transits.  There is a smattering of astrometry  and tracking down of extragalactic globular clusters. This work is done with a 0.4m Dilworth, SX 814 CCD camera and a selection of photometric filters.

In Cambridge I have a very poor sky --- restricted and polluted --- so little work gets done. The 0.25m Dobsonian is carted out onto the lawn where I will make visual estimates of VS and occasional sight seeing visits to doubles and the brighter Messier & NGC objects. This winter I really must see what can be done with a DSLR and/or video camera plugged into the Dob.

2 hours ago, clean said:

My main question is this - Will the stock 10 and 25MM 1.25" eye pieces satisfy? or are we better served to purchase a decent quality wide 2" eye piece to get started?  perhaps something in the $1-200 range?  I want this to be as easy as possible for him to jump right in.

 

 

As others have said, purchasing new eyepieces can and should wait until you have experience with the ones you have.

Something I have found invaluable is a Bahtinov mask. Mine came from Rother Valley Optics and cost less than £20. I've no financial interest in RVO, just a satisfied customer.  You appear to live somewhere the local currency is in $, not £, but it seems very likely that you should be able to find a local supplier who will sell you one at comparable cost.

A Bahtinov mask  makes focussing really easy. Before using one I used to have great difficulty because my eyes would insist on refocussing themselves all the time and I would be forever trying to get a sharp view. With one my eyes have no choice but to accept the true focus and they seem to hold it after the mask has been removed.