miguel87

Ah ok, I dont have goto or anything so had to wait until I could find venus naked eye and go from there. Was half an hour after sunset by the time I got it in the scope. Thanks 👍

Was the flash you saw quite low almost due west?

I got the scope onto mercury too but the seeing was awful, obviously it is low but I had a huge amount of atmospheric CA and a VERY jumpy planet too. No hope of surface detail. Is this standard or can you catch it on better days. I dont know how good it gets?

Yep my first ever mercury too! My sky is NOT looking good tomorrow so glad I caught them both tonight.

Will become visible in the evenings as a thin crescent over the next few days.

For whatever my view is worth too... I think we could boil it down to the question of whether the airy disc changes size or not. Because the star is a fixed brightness that doesn't change. So IF it does get bigger, surely it MUST dim? IF it doesnt change size then it shouldn't change brightness? 🤷‍♂️

Very nice transit shot! If nothing else, it's an opportunity to try out my highest magnification 😄

Are you gonna give it a go over the next few days? OK, well it will be pleasant just to resolve the disc in my trusty newt! ✌

Thanks john. Quite excited to tick it off the list even tho I am not expecting a spectacular display! Any hope of surface detail?

Apparently it should be an easy find tonight and my forecast is clear until midnight. Do plan to set up and observe it through twilight. Quite excited as Mercury is the only major planet in our solar system that I have not observed! Any tips for a first time mercurian?

Or if it makes more sense I could say how it would appear using a hypothetical perfect camera with pixels less than half the size of photons.

An object has a objective luminance, a level of electromagnetic radiation in the visible spectrum, even if nothing observes it. These values can be calculated even if they are not measured. Same as a tree makes a sound when it falls even if nobody hears it.

Thanks Vlaiv, that explains in more detail what I was trying to understand. The thing that struck me was that when looking in the telescope you are not viewing the actual star. But the image created by the telescope, I just couldn't get my head around how this could be a point source with no measurable physical dimensions when it existed only inches in front of my face! I totally understand that the disc the scope produces is tiny and any changes in size and brightness may not be perceptible to us at all. I was just interested in what the telescope was actually doing with the light. Sorry for bringing you into this again @vlaiv 😂 you were just the only person who seemed to understand what I was getting at. I now have an understanding and perhaps most people think it is wrong. Perhaps it IS wrong. But I don't want to cause trouble so I will stop where I am. ✌

I do accept this is what is seen with the eye. I'm really trying to explain that this is not what I am talking about but I think that is the problem. People keep repeatedly going back to how things appear to the human eye. Which is very informative but it's not the question I was asking. I was just trying to resolve two pieces of information I had been told which conflict each other that is all. 1)a star is a point source as does not dim under magnification. 2) you can resolve a stars airy disc under high magnification. I'm very sorry if I offended anyone I just wanted to know how the telescope manages to produce both a point source and extended object at the same time. But people just keep talking about limiting magnitude and the human eye and telling me I am not understanding. Vlaiv did understand and said that yes, stars are not a true point source in the telescope but appear that way until at least 85x and then it might be possible to see them dim visually. I just took this a step further logically and thought that despite the limitations of the human eye, the image of the star must actually grow and shrink with magnification like any other object, but the size of it is so tiny that it is difficult to see. When I make this point I am told it is irrelevant to the use of a telescope. (Not helpful). So yes I am challenging the common held belief that stars do not dim under magnification. I have good evidence and theory to do do and even some well respected members who agree with me So if challenging long accepted beliefs is arrogant then fine, I am arrogant. But it also seems that I am right. Now I'm not saying that anyone else in this discussion is wrong, they are just answering a different question about what the human eye can see. And I can't seem to manage to get people to realise that is not what I am talking about. Apologies again.

If you can give me an example I will happily apologise. I am actually very grateful for the input. What is actually happening is that more experienced members are being listened to and I am not. But I didnt expect anything different. People just want to tell me I'm wrong but we are discussing different topics. When I try to explain people say I am being rude. With the exception of Vlaiv who understood what I was saying. I am interested in how a telescope works and produces images. I was interested in the issue of stars and point sources and how the airy disc worked and how an object could be both point source and extended. I am not concerned with human perception. Just the process of what the telescope does. There's nothing wrong with that. And with all due respect, number of posts on a website has no bearing on knowledge. There is many people in the world with much better knowledge than all of is and they have zero posts on this website.

Good luck, make sure you share the results 👍

Seems like you havent actually been reading the posts on this topic so it's kind of hard to continue the conversation. I have addressed all the points you make above. Even calculating more precisely the size 'in human pixels' of a star and they are much bigger than one tenth of a pixel. And the increase in size will be visible from approx 85x to the human eye, even calculating for the uneven distribution of light. Also the graph showing the spread of light of the airy disc has already been posted and discussed. Also already been said but the airy disc isnt something that 'becomes visible' at a certain point. The airy disc IS the telescopes image of the star produced at the focal plane, there is no other image of a star that it is able to produce. If you can see a star, that is the airy disc, just really small or bigger. So as I said above, the point at which the human eye can detect this given various different factors is not what i am discussing. You also say that it is not relevant to the use of telescopes. Great, I never said it was. I'm just stating that the image of the star dims with magnification as part of my understanding of how a telescope works and produces an image. I was confused at how a star was a poont source but then suddenly not a point source as any increase in size under magnification must be physically linear. I starting looking into how a telescope 'makes' an image of a star If you saying 'it's not relevant', is saying yes it's right then that's fine. And it seems strange to tell me it's not relevant. To who is it not relevant? It is obviously relevant to me else I wouldn't be discussing it. You don't have to reply to my messages, especially if you haven't read all the previous ones.

You need to hook a computer up to your telescope to use a polemaster I believe.

Also if you are arguing that the eye doesnt perceive this change in brightness then that is a different point. You could write an accurate scientific description of why my mobile screen appears brighter at 1am in the morning than 2 in the afternoon. I'm sure this includes, contrast, eye adaptation and many other factors. But the fact remains that the screen is NOT brighter. Equally you can explain why the stars do not appear to dim under magnification: human eye resolution, contrast etc. I am arguing that even though this may be the case, there is still a separate truth about whether the image of the star produced by the telescope actually, physically does dim.

The measurable difference in brightness changes. Also I am not claiming to know much about contrast or limiting magnitude. All I am saying is that a star dims under magnification. We already discussed the point at which this should be noticeable. My maths made it about 50x mag and Vlaiv (much more trustworthy!) has info to suggest about 85x mag. Going back to basics we know the star looks bigger under high mag because the airy disc takes up more of the apparent FOV at say 200x than the star does at 30x mag. How can an object with a fixed brightness not have its brightness spread out as it gets bigger?

Haha, if only things were simple! Thanks for sharing I will definitely have a read 👍

Not true. All degrees given are apparent through an eyepiece not degrees of the celestial sphere. Imagine an object (A) of 10degrees squared surface area has a total brightness of 10. (0.1 brightness per degree squared) Another object (B) of 0.1degrees squared size and total brightness of 100. (10'000 brightness per degree sqaured). There is a difference in surface brightness of 9'999.9 per degree squared between the two objects in the FOV. Now magnify 10x Object A is now 100degrees squared (0.001 brightness per degree squared) a reduction of 0.099 per square degree. Object B is now 1 degree squared (100 brightness per degree squared) a reduction of 9'900 per square degree. The difference in surface brightness is now 99.999 Much less difference. So contrast can change between two extended objects at different magnifications Even if one object did not change in size or brightness as you suggest, the surface brightness of the other object still changes. so either way, if a star functions as a point source or not, contrast will still change.

I agree with this. And actually I think a 10 inch EQ is borderline. I have owned 5, 6, 8 and 10 inch EQ mounted nets and chose to settle down with the 8 inch despite the reduced light gathering. I have never tried a 12 inch but the 10 once set up was such a beast, and if there was even 10mph of wind it was a nightmare, eyepiece positions are challenging at times and I just would not have used it half as much as I use the 8 inch.

Thanks, I use a really cheap pencil from my corner shop that isnt even marked HB or anything. And the paper is a sketch pad from amazon, decent thick paper tho, I can send you a link if you are interested. Then obviously just invert the image on my phone once I have photographed the page. To be honest what ai do is a sketch at the eyepiece on lower quality paper, then I can tody this up in daylight the next day, making sure my star spots are round and my nebulosity is smudged well and not scratchy. I use a biro to make brighter stars brighter for a bit of contrast and that's it. I only started a couple of months ago but it is suprising how fast you can improve.