A sun-synchronous orbit (SSO) is a near-polar low-Earth orbit whose plane precesses to keep a fixed local solar time at each equator crossing, so a satellite images every location under consistent sun illumination.
Most optical Earth-observation satellites fly sun-synchronous orbits because consistent illumination makes images comparable over time — essential for change detection, vegetation monitoring, and time-series analysis. The fixed crossing time is often described as a 'local time of descending node' (e.g. 10:30 LTDN).
Because SSO is near-polar, these satellites pass near both poles each orbit and provide near-global coverage as the Earth rotates beneath them, with more frequent passes at higher latitudes.
So every scene of a given location is captured at roughly the same local solar time and sun angle, making images comparable over time for change detection and monitoring.
Many are, but SAR does not depend on sunlight, so SAR constellations have more orbital freedom; consistent lighting is an optical-imaging concern.
Plan a real acquisition over your area on the interactive map, browse the satellite catalog, or read the tasking guides.