Skymapper DR1 now publicly available!
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The Southern sky, finally!!
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And it is disappointing, even DSS images are better.
Sigh
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Ghost_Sheep_SWR
in response to Ghost_Sheep_SWR's comment.
You can view and compare with other surveys here, based on Aladin light tech:
http://skymapper.anu.edu.au/sky-viewer/
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JeanTate
in response to Ghost_Sheep_SWR's comment.
Great news that Skymapper DR1.1 is out! 😃
And it is disappointing, even DSS images are better.
That's sad ... why do you think this is?
From what I read, Skymapper has six filters, vs DSS's three (though some parts of the sky do not have coverage in all six). Also, doesn't Skymapper go deeper (18 mag, or 17.5 depending on filter)?
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Ghost_Sheep_SWR
in response to JeanTate's comment.
Agreed six filters is better vs three filters, or in this case I tend to think of it as two (DSS Red + Blue) vs three (g r i).
I think some areas / objects might be better because the difference there can be between short and long Skymapper exposure times.
But to compare I'm not interested in the rare object that has better imaging, but in all objects on average across the sky. Therefore I just took some random faint galaxies and compared them between the two surveys. Every one of them was worse in Skymapper. It can be seen in the skyviewer link I provided.
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And what is happening with the timeframe of Talk? Have we entered a timeloop here???
I did not post above message '5 hours ago', it is 5 minutes max!!
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JeanTate
in response to Ghost_Sheep_SWR's comment.
or in this case I tend to think of it as two (DSS Red + Blue)
DSS has two iterations, and in the second (DSS2) there's also "IR". At least, there is, per SkyView. I do not know how much of the southern sky was imaged in DSS2 IR.
But to compare I'm not interested in the rare object that has better imaging, but in all objects on average across the sky. Therefore I just took some random faint galaxies and compared them between the two surveys. Every one of them was worse in Skymapper. It can be seen in the skyviewer link I provided.
Ah now I see what you mean! 😃
Yes, the resolution seems no better, which may not be all that surprising given the equipment used.
However, I think the SkyMapper data is much better than the DSS data, in many respects. For example:
- the photometry is surely much better, in all bands, if only because of the superiority of CCDs over photographic plates
- SkyMapper FITS files with the data will have a linear relationship between data and intensity (up to saturation), whereas DSS data has a non-linear one (which varies from plate to plate too!). This should be obvious if you view the FITS using something like DS9
- six filters (ideally) vs three
- the SkyMapper filters are more suited to today's astronomy research than those used by DSS, if only for the more consistent and uniform wavelength response (DSS, being based on photographic plates, has greater plate-to-plate and night-to-night variation)
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Ghost_Sheep_SWR
in response to JeanTate's comment.
Ofcourse, all very good points.
For me I guess the disappointment stems largely from the premise of 'SDSS of the South'.
If you keep your first DR locked away for months AND cannot equal DSS(2) that's misleading at the least. I probably should have known better and have done some research on what's actually possible with a mirror of that size.
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ElisabethB
moderator
in response to Ghost_Sheep_SWR's comment.
It is/was a known issue and is resolved as of a couple of hours ago (I think ! 😉 )
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Ghost_Sheep_SWR
in response to ElisabethB's comment.
ah yes saw the thread, thanks! 😃
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