6 replies to this topic

[BQ Octantis]

Quite clear tonight, so I got another chromaticity measurement through the C5. It's still quite blue.

 

Celestron C5/750 f/6 SCT, Canon 600D/T3i, 39×30sec, 300:1 px

 

Cheers,

 

BQ

 

[BQ Octantis]

Here's what I get for an average chromaticity:

 

 

Still blue hot!

 

BQ

 

[BQ Octantis]

Hi everybody!

 

Someone pointed out how far off the hues are in the public domain Planckian locus diagram on Wikipedia (which I used for the plot above). I picked it because it was one of the few depicting the locus out to infinite temperature, but the Planckian formulas fall apart well below that. So I went back and made my own out to 20,000K.

 

I also found a plot of the event's calibrated spectrum taken just two hours after I shot my data, which provided a source for a spectrum-based chromaticity calculation (using Bruce Lindbloom's calculator with 5 nm spaced CMF inputs across the visual band). The spectral data didn't quite cover the full visual band, so I extrapolated both ends to the edges with an exponential curve fit, which fit the data better than any other basic curve.

 

So here's the new and improved chromaticity diagram with D65 hues, complete with the reference chromaticity value computed from the spectral data:

 

(Click for full size.)

 

As to what the two colors look like and how they compare, I replaced the high-scatter chromaticity values in the image with a single chromaticity, once with the spectral value and once with my C5 value. Here's what they look like side-by-side:

 

 

While subtle, I can certainly see the slight greenish tint on the left and the slight reddish tint on the right.

 

Cheers,

 

BQ

Edited by BQ Octantis, 27 May 2023 - 08:50 PM.

[vidrazor]

Not that I understand it, but what do we deduct from it?

[BQ Octantis]

Well…um…

 

It's blue. Defo. With high confidence.

 

To tell you that, it's only taken me

 

• 6 months of study
• 90 calibration test swatches
• 79 Excel spreadsheets
• 24 Python scripts
• 5 Octave scripts
• 100 CCMs
• 1000 lines of code

 

 

 

Maybe I need a different hobby!

 

BQ

[BQ Octantis]

I jest, of course. For me, the journey was worth the effort. Much like internalizing the physics of mechanics—when all the world looks like vectors and free-body diagrams—everything to me now looks like a chromaticity diagram. And I'll never look at "saturation" or "stretching" the same.

 

As to the CCT of the supernova, from the measurement it's quite clearly around 18,000 to 19,000K. At an apparent magnitude of 11 at 6.4 million parsecs, I calculate its absolute magnitude as -3.5. Putting that on a Hertzsprung-Russell diagram, the supernova is practically on top of Achernar.

 

[Source]

 

If we've seen Achernar then we can relate to the supernova's color-brightness relationship. So if someone exclaims, "That's more luminous than an entire galaxy! Have you ever seen anything so bright?" you can respond, "Yes. Yes I have."

 

BQ

Edited by BQ Octantis, 28 May 2023 - 04:47 PM.

[BQ Octantis]

So now I'm wondering…why aren't there other Achernar-level stars visible in the galaxy? With a trillion stars, there are bound to be at least a few! But there are none:

 

(Click for full size.)

Celestron C5/750 f/6 SCT, Canon 600D/T3i, 39×30sec, bin2 (average)

 

Must be some pretty steep extinction at 6.4 million parsecs…

 

BQ

 

P.S. Did you notice how I used the star color for the marker lines?

Edited by BQ Octantis, 28 May 2023 - 05:52 PM.