Today's APOD

[Ags]

I do like a good APOD and today's is an amazing close in view of a planetary system being formed, combining visual and IR light.

https://apod.nasa.gov/apod/ap210622.html

The star HD 163296 is an A1V star about 330 light years away.. That dust ring looks about 200 AU across which means that it is 2 arcseconds wide. Pretty sharp optics from ALMA! Also the polar jets imaged in visible light - it seems to me to be undersampled - I wonder how big the pixels were?

[vlaiv]

It says that telescope has angular resolution of 0.2 arc seconds for imaging and has 120m focal length (VIMOS instrument capable of imaging in 300-1000nm range - not sure if that was used).

That would make pixel size - ~116µm.

 

[Ags]

That agrees with what I see in the image, but the visible light channel looks really undersampled...

[vlaiv]

It will certainly be "undersampled" compared to ALMA which has 0.01" resolution - or about x20 higher than VLT.

[Ags]

I am not explaining myself well. I am not comparing the visual channel to the ALMA channel which benefits from massively more aperture. I am comparing the visual channel with itself - it is so blocky with such stark jumps in brightness between adjacent pixels, I just seems to me they could have got away with smaller pixels.

[vlaiv]

2 minutes ago, Ags said:

I am not explaining myself well. I am not comparing the visual channel to the ALMA channel which benefits from massively more aperture. I am comparing the visual channel with itself - it is so blocky with such stark jumps in brightness between adjacent pixels, I just seems to me they could have got away with smaller pixels.

But if you look at this version - I think it's all fine:

If you have such large mismatch in resolution between two images and you want to make compound image - well, you need to rescale one of them to match their scales. You can either loose detail in more resolved one - or simply make less resolved one look bad - without detail.

Fact that these two telescopes have very different resolving power - order of magnitude different - makes it hard to match resolutions and hence - one source needs to suffer.

Authors chose visual to be largely scaled up to match resolution of radio and that made visual channel look bad - but it is not bad itself when viewed at proper scale to itself.