AkastroidThe Moon
Moon stacking for Mac, Windows and Linux
Drop in a lunar video or a folder of frames. Akastroid grades every one, keeps the sharpest, aligns the surface in pieces so the atmosphere's local warping comes out, and gives you six scales of sharpening that re-apply as you move them.
The same application does planets and deep sky. It runs natively on a Mac, where AutoStakkert, RegiStax and PIPP are Windows-only. What runs on macOS and what does not.
Free to try. Your images are not uploaded, and there is no account to create.
Real captures: a ZWO ASI585MC recording AVI video, stacked and sharpened in Akastroid. See more in the gallery.
The Moon is bright
Nothing about lunar imaging is limited by how much light there is. The exposure is a fraction of a second, the contrast is enormous, and a single frame already shows craters. What ruins the picture is the atmosphere: a few kilometers of moving air that smears the detail differently in every frame, and differently in different parts of the same frame.
The answer is lucky imaging: record hundreds or thousands of very short frames, keep the ones the turbulence happened to leave sharp, align them, average them, and sharpen what comes out. It is the same approach used for the planets, and the Moon's size puts more strain on one part of it than any planet does.
Multi-point alignment
A planet is a small disc; a lunar close-up fills the sensor. Over a field that wide the seeing is not one blur but many, and aligning the frames as a single rigid object gives you a sharp edge and a soft middle, or a sharp middle and a smeared limb, because the misalignment averaged the detail away before the sharpening ever ran.
Akastroid tracks the surface on a grid of alignment points spaced automatically from the frame, and the points are placed where there is real structure rather than spread evenly over whatever happens to be in frame. Each point is ranked separately across the frames, so a region that was sharp in frame 40 contributes there even if the rest of that frame was soft.
Grading
The obvious way to score a frame's sharpness, the energy in its finest detail, gets short exposures backwards, because the finest thing in a noisy frame is the noise. Score that way and the grainiest frames rise to the top of the list and into your stack.
What is measured instead is the structure at the scales lunar detail occupies, divided by the noise in that same frame. You set the percentage to keep, with a graph of the whole capture showing how the seeing moved while you were recording.
Detail below the pixel scale
Most lunar captures are undersampled: the optics resolve more than the sensor's pixels record. When the disc is small in the frame, the survivors are integrated onto a finer grid, which recovers detail from the sub-pixel shifts between frames rather than only enlarging what was there.
Mineral color
Titanium-rich maria are slightly blue and the highlands slightly warm. The differences are a few percent, well below the noise of any single frame and measurable in a stack of a few hundred. Once the stack exists, saturation takes those differences from technically present to visible, and every adjustment re-renders immediately because the stack is not rebuilt.
Atmospheric dispersion is corrected first, for the same reason it matters on a planet: a low Moon arrives with its color channels displaced, and saturating a dispersed stack turns a real blue mare and a refraction artifact into the same thing.
Close-ups that fill the frame
The closer you get, the less of the Moon's edge is left in view, and the edge is what most stackers line frames up by. When the Moon touches the frame edge, Akastroid stops looking for a disc that is not there and registers every frame by matching the surface itself across the whole picture, so a close-up that drifted while you recorded it stacks sharp instead of doubling every crater.
What this replaces
The traditional lunar chain is a pre-processor, a stacker, a wavelet sharpener and sometimes a stitcher: four programs, all free, all Windows-first, each with its own conventions. Akastroid does the common path through them in one window, on a Mac as well as a PC, with the grading graph and the sharpening sliders on screen together so you can move between them without exporting anything.
If you would rather read about the photography than the software, the guide on photographing the Moon covers phases, exposure and why the terminator is worth waiting for.
Planets and deep sky
Planets take the same lucky imaging path, and nebulae and galaxies the deep sky path, in the same application and under the same licence.
Is there one app that does planets, the Moon and deep sky?
Akastroid does both. The usual planetary tools (AutoStakkert, RegiStax, AstroSurface, Lynkeos) do planets, and the usual deep-sky tools (Siril, DeepSkyStacker, PixInsight, Astro Pixel Processor) do deep sky, because lucky imaging on a thousand video frames and integrating ninety five-minute sub-exposures are different jobs. Point Akastroid at a SER or AVI of the Moon or at a folder of deep-sky lights and it works out which it has and runs the matching pipeline. It is one licence, on Mac, Windows and Linux.
Can I stack a video of the Moon, or does it need stills?
Either. A SER or AVI capture takes the lucky imaging path: every frame graded, the sharpest kept, aligned in pieces and averaged. A folder of stills works too. Video is better for a close-up at high magnification, where the seeing changes between one frame and the next; stills are fine for a whole disc through a short lens.
Why is my stacked Moon soft in the middle and sharp at the edge?
Because it was aligned as one rigid object. The atmosphere does not only shift the Moon, it warps it, and across a field as wide as the lunar disc, the warping is measurably different from one crater to the next. Aligning on a grid of points across the surface takes that out before anything is averaged. More than any other setting, this decides whether a lunar stack comes out soft or sharp.
Can it bring out the mineral colors?
Yes. The colors are real (titanium-rich maria run blue, the highlands run warm) and they are in an ordinary color camera's data, several percent apart. Stacking is what makes them usable: the differences are far below the noise of a single frame and survive averaging. The saturation control then takes them from technically present to visible, and because the stack is already made, moving it re-renders immediately.
What about the terminator?
The terminator is where the detail is, and it is also the hardest part to expose, with shadows close to black beside a lit crater rim. Frames are graded on the structure your capture holds rather than on raw contrast, so a frame is not favored for being noisy, and highlight protection keeps a bright rim from clipping into a flat white edge while the shadow detail is stretched.
Do I need to crop the capture first?
No. The disc is found, the stack is cropped around it with generous margin, and the alignment points are placed where there is real detail rather than on empty sky. There is no separate pre-processing step and nothing to convert.
My Moon has a blue edge on one side and a red edge on the other.
That is atmospheric dispersion, and it happens whenever the Moon is low: the atmosphere refracts blue more than red, so the three color channels arrive slightly displaced. Red and blue are realigned to green before sharpening. Done afterwards, the sharpening has already turned the fringes into something no alignment removes cleanly.
How long does it take?
A capture of a few hundred frames finishes in seconds, and the sharpening sliders re-apply without re-stacking, because changing them does not rebuild the stack. A capture of tens of thousands takes longer to grade, but adjusting the sharpening afterwards does not repeat that work.
My close-up fills the frame, or the Moon runs off the edge. Does that work?
Yes. When the Moon touches the frame edge there is no whole disc to line up by, so frames are registered by matching the surface itself (the craters and the terminator) across the entire frame. A capture that drifts as you record it stacks sharp instead of ghosting.
Can it stitch a mosaic of the whole disc?
Not yet. The mosaic tool places panels by their stars, so it is built for deep-sky fields, and a lunar panel has no stars to match. Each lunar close-up stacks and sharpens fully on its own.
Try it on your own Moon captures
Free to try. There is no account, and nothing is uploaded. A few hundred frames take seconds.