Stacking is a process used in astrophotography to improve the quality of images of celestial objects, such as stars, galaxies, and nebulae. It involves combining multiple images of the same object into a single image, effectively reducing the noise and improving the signal-to-noise ratio.

When taking a photograph of a celestial object, there are several sources of noise that can degrade the image quality. These include noise from the camera sensor, atmospheric turbulence, and light pollution. By stacking multiple images of the same object, the noise in each individual image is reduced, while the signal (i.e., the light from the object) is increased.

The process of stacking involves aligning and combining multiple images of the same object, typically using specialized software such as DeepSkyStacker or ASTAP. The software analyzes each image and determines the position of the object, aligning each image to a common reference point to compensate for any drift or movement during the exposure.

Once the images are aligned, they are combined into a single image using various techniques such as median or average stacking. This final stacked image has a much higher signal-to-noise ratio than any individual image, resulting in a cleaner, more detailed image of the object.

Overall, stacking is a powerful technique used by astrophotographers to capture high-quality images of celestial objects. By combining multiple images, the signal-to-noise ratio is improved, allowing for greater detail and clarity in the final image.