by Nitpicker » Sat Nov 09, 2013 10:07 pm
Chris Peterson wrote:Cousin Ricky wrote:The big question (the “incongruity”) is why the diffraction spikes are not smeared to the extent that the stars are elongated. Damian, please help us out!
It isn't clear to me that they aren't. Since the diffraction spikes are at 45° to the direction of elongation, we'd expect the broadening to be the same for both axes, meaning there is no simple way to detect it.
That said, the saturated (or nearly saturated) stars that show diffraction spikes might be slightly less elongated, suggesting a masking technique that resulted in fewer of them being stacked- not an unreasonable thing to do.
I appreciate all the comments on the diffraction spikes. I have learnt a few things. (I hadn't even considered that they might have been added after the fact [or not]. Quite a foreign concept to me.) All I did know was that they are unavoidable with certain telescope constructions, based on the kind of mounting of the secondary mirror or diagonal, or similar. I tend to find diffraction spikes distracting, in much the same way that sparkly dresses worn by beautiful women can be distracting. But maybe that is the point. Still, I'm more interested in the stars (and the women) than the sparkles.
Edit: I realise that any unresolvable point source of light can only ever be observed as a diffraction pattern. But are some patterns better (or more natural) than others?[quote="Chris Peterson"][quote="Cousin Ricky"]The big question (the “incongruity”) is why the diffraction spikes are not smeared to the extent that the stars are elongated. Damian, please help us out![/quote]
It isn't clear to me that they aren't. Since the diffraction spikes are at 45° to the direction of elongation, we'd expect the broadening to be the same for both axes, meaning there is no simple way to detect it.
That said, the saturated (or nearly saturated) stars that show diffraction spikes might be slightly less elongated, suggesting a masking technique that resulted in fewer of them being stacked- not an unreasonable thing to do.[/quote]
I appreciate all the comments on the diffraction spikes. I have learnt a few things. (I hadn't even considered that they might have been added after the fact [or not]. Quite a foreign concept to me.) All I did know was that they are unavoidable with certain telescope constructions, based on the kind of mounting of the secondary mirror or diagonal, or similar. I tend to find diffraction spikes distracting, in much the same way that sparkly dresses worn by beautiful women can be distracting. But maybe that is the point. Still, I'm more interested in the stars (and the women) than the sparkles.
[i]Edit: I realise that any unresolvable point source of light can only ever be observed as a diffraction pattern. But are some patterns better (or more natural) than others?[/i]