Mars and Infrared

 

My picture of Mars, earlier this week, is made using my ASI224MC camera. The ASI224MC, is a color camera with some good respons in the near infrared. As I did not use an IR/UV blocker  the picture is an IR picture polluted with visual light -see also article "why you should use an IR cut filter with a  color camera". The color of my Mars picture is reddish/pink which is not a realistic color. I saw different pictures of Mars from other amateurs which are using an IR/UV blocking filter. Threrofor I ordered an IR/UV blocker  with the following properties.

On top of this I will purchase two IR bandpass filters: 642 and 742nm IR bandpass filters. Below is a graph showing the IR bandpass and the sensitivity of the ASI224MC camera.

RGB lines represent the sensitivity of ASI224MC
642, 742 and 807 are graphs of the IR bandpass filter.

The vertical lines are emission lines as a reference eg. H-alpha, OIII, Na, Hg

The grey line in the back is a typical curve of an astrosensor.

Mars Reworked - R,G,B split with PIPP and WinJupos

It had been a while since I photographed Mars. On Sunday, November 13, the conditions were favorable with a completely open sky. As a setting I had my TAL200K with ASI224MC camera. Furthermore an ADC and barlow x2. The polar alignment went flawlessly with an “excellent” result and only 8 arcseconds deviation! In total I have been outside for 3 hours and I have made 8 shots of 3000 frames (145fps). The recordings were made via SharpCap 4 and saved in SER format. 

On Monday morning I have the SER files with AS3! stacked and edited in CS4. Personally, I didn't think it was bad and could compare the details with the Mars Mapper. However, I received feedback from Johan R and Walter about: where the polar cap was and why the picture looked so red. In the meantime I had also sent my photo through the VVS maillisting where I received the same feedback from Geert VDB and Luc DS. So back to the drawing board. Most planetary photographers shoot with mono cameras and RGB filters. Few do it with a color camera and that's where the problem is. The colors of a color camera do not always correspond with reality, so with the ASI224MC. The white balance must be adjusted to R52(R58) and B99(B99). Since the recordings had already been made, I got the tip from Walter to split the SER files into R, G, and B images. This was done with PIPP software. Then stacking with AS3! (25% retention of the frames). Using WinJupos I then merged the obtained R,G,B photos where the gamma of Blue is 2x higher than R and G. This way I get an RGBB image. This image was edited in CS4 and in DeNoise AI. 

The result is a beautifully detailed Mars image with a more realistic color and a visible polar cap. A satisfied amateur astronomer 😊

Mars - November 13, 2022 - Compared with Mars Mapper

Picture of Mars from November 13, 2022, UT22h58 with fair to good seeing conditions.

Setting: TAL200K f/8.5, ASI224MC with ADC and Barlowx2

Software: SharpCap 4, AS3!, CS4, DeNoise AI

Picture is compared with Mars view from Mars Mapper - see this link. Details are matching well.

Mars - My first picture 2022

My first close-up picture from Mars this year. The red planet is currently 0,57 AE away from Earth and is 97% illuminated. The angular diameter is about 16,4".

Setting: TAL200K f/8.5 with ASI224MC and ADC, Barlow x2

Software : SharpCap 4, AS3! (25% stacked), CS4 and DeNoise AI

Calculating Limb Darkening Coefficient

I calculated the Limb Darkening Coefficient from the Linear Limb Darkening law assuming a plane-parallel solar atmosphere.:

As a base, I used a picture from the solar disk taken during the recent solar eclipse with an OIII filter (500nm). Using ImageJ software I was able to plot the intensity (limb darkening) graph by retrieving the gray intensity data per pixel. Using above formule, I calculated the Linear Limb Darkening coefficient (LDC). To calculate the LDC, I took the average LDC's of the radius between 0,9 and 0,3 . This results in a LDC of 0,22 (500nm)

I put this data together in a graph which combines the intensity graph from ImageJ and the theoretical derived graph with a LDC of 0,22.

Discussion:
In the literature I found LDC's  of around 0,8 (eg. Dias-Cordoves see this link)  

Conclusion : my LDC calculation is not really near the ones published in different studies. 

See also interesting LD calculators like the one for the James Webb Telescope. See this link

Dynamic of Sunspot group AR3141 and AR3145

Picture of sunspot group AS3141 and AR3145 on November 11 and 12.

 

Sunspot AR3141 - CaK and White light

 

Sunspot AR3141, AR3140 and AR3145 observed on November 12, 2022. Sunspot AR3141 not only photographed in White Light but also with CaK filter.

Setting : TAL200K f/8.5, ND3.8 filter, CaK filter, ASI290mm, Barlow x2

Software : SharpCap4, AS3! (50% stacked), IMPPG, CS4