Imaging the Moon in daylight

On the morning of the 13th October at around 7:20 am, Ispotted the 18 day old Moon about to disappear behind the apple tree on thewestern side of my garden.  Theatmosphere seemed very clear so I decided that it was worth imaging.  It was not visible from my permanent mount,so I set up my iOptron MiniTower with a 90 mm triplet refractor and AltairAstro 294 astro camera acting as a webcam. I was just able to capture a video sequence  before the moon passed behind the tree – but Isuspect that it was already reducing the amount of light falling on its easternlimb.

The video sequence of 217 frames was aligned and stacked in Autostakkert.  There is always a compromise when deciding the percentage of the data to stack.  I initially stacked the best 50%, so just over 100 frames. By only stacking the very best frames one hopes that a sharper image will result but then the image will be noisier and so will allow less sharpening in post processing.  I also tried stacking the best 25% but there was no significant difference.  If anything, I preferred the result from the 50% stack.

Post processing in Photoshop

I processed the output from Autostakkert in an academicversion of Adobe Photoshop CS4 but  thesame steps could be carried out in Affinity Photo (sometimes available for £30)and even the new free program, GLIMPS.

The output image showed a green cast (as usually found when using astro cameras), but with quite a large blue content from the brightening sky. 

This is easily removed by a four step process:

1) Duplicate the image.

2) Apply a small (6 pixel) Gaussian Blur to the toplayer – this is so when the background colour is selected it is the average ofa few pixels.

3) Use the paint brush to select the background skycolour away from the Moon and paint the whole layer this colour.   (One is assuming that the sky glow isuniform across the frame – at least across the Moon.)

4) Flatten the two layers using the ‘Difference’blending mode.  

The result is shown below.

As, given the sky glow, one is unlikely to be ableto produce an enhanced colour image of the Moon it is then best to change thecolour mode to Greyscale.   The image wasquite dark and can be lightened using the brightness tool. 

The eastern limb area was rather dark, so I selectedthe region with a 100 pixel feathered ‘Polygonal Lasso Tool’  and brightened it.

The ‘Levels’ tool was used to bring up the blackpoint.

[If one were using a telescope with an achromaticobjective, a slightly better image might be achieved by splitting the imageinto channels and using the green channel as the monochrome image.  As the telescope used was a tripletapochromat, I could see no difference between the greyscale and green channelimages.]

Sharpening in Images Plus.

The free program, Images Plus, includes under its‘Smooth Sharpen’ Menu the ‘Adaptive Richardson – Lucy Restoration…’ sharpening tool. 

This applies ‘deconvolution’ sharpening to the imagewhich attempts to recover the image that would have been seen without theblurring effects of the atmosphere.  Itis thus a true sharpening method. 

 I applied 20iterations but one can experiment to see the result as more iterations areapplied.

Selecting the number of iterations
Sharpening in progress.

The output from Images Plus was rotated.

Rotated output from Images Plus

One could then, perhaps, apply a little ‘actuance’ sharpening using ‘high pass sharpening’, ‘unsharp mask’ or the ‘smart sharpen’ tool in Photoshop.  [This is not true sharpening but enhances the transitions between light and dark so making the image appear sharper.]

One can also use the ‘unsharp mask’ filter with a large radius and small amount to apply some ‘local contrast enhancement’.

The final result is seen below – which I find quitepleasing.  It is not often that I havetried to capture the 18 day old Moon.  Over in the west is Aristachus, the brightestcrater on the Moon’s surface.

In the half size crop, the mountains that form thewestern edge of Mare Crisium show up well as do the two craters and rays ofMessier and Messier A.

Homage to Isaac Newton

I was able to take an image of the apple treeadjacent to the Moon and produced this composite image.

The 21 day old Moon on the 16th October 2022

This was another beautiful early morning and the 21 day old Moon was high in the sky at an elevation of 50 degrees.  This time I used a Takahashi FS102, 820 mm focal length, telescope with the AA 294mc Pro colour camera used as a webcam.  The image processing steps were identical  to those applied to the 18 day image.  Due, I suspect to the high elevation and excellent seeing, the resolution of the image was somewhat greater at around 1.6 arc seconds.  Interestingly, this is exactly the size each pixel subtended on the Lunar surface  (perhaps not too surprising).  Aristachus in the west is very prominent and the region around Plato and Clavius showed up well.

21 day old Moon
The Plato – Clavius region
© Ian Morison