CMOS is often preferred for high-speed astrophotography mainly because it can be read out faster and with lower read noise. In a CCD, charge is shifted across the chip row by row to a transfer register, then converted and amplified, typically using external ADC hardware. That longer analog path and serial-style readout can limit speed and add noise.

In a CMOS sensor, the signal is converted much closer to the pixel array, often with ADCs on the same chip and sometimes multiple ADCs working in parallel. That allows much faster readout, which is valuable when taking many short exposures of moving targets or when atmospheric seeing changes frame to frame.

Lower noise is also a major reason astrophotographers like CMOS, since astrophotography is very noise-sensitive. CCDs can still have advantages, including pairing with very high-quality external ADCs for strong dynamic range, so CMOS is not automatically “better” in every case.

A separate but important issue for serious astro work is cooling. Dedicated astro cameras, whether CMOS or CCD, are often preferred over regular consumer cameras because they can be cooled more aggressively, reducing sensor noise during long sessions.