Synoptic Optical Long-term Investigations of the Sun (SOLIS) is a synoptic facility for solar observations over a long time frame that is funded by the National Science Foundation (NSF) and designed and built by the National Solar Observatory (NSO).

The final f/6.6 full-disk solar image is focused on a spectrograph slit that is cooled by a flow of chilled water-propylene glycol solution.

To improve the internal seeing, the VSM is sealed by 74 cm diameter, 6 mm thick fused silica window.

The FDP provides full-disk images of the Sun in a variety of spectral lines with a cadence as high as 10 seconds.

SOLIS was located on top of the Vacuum Telescope building[6] at Kitt Peak National Observatory until July 2014,[7] then temporarily moved to the University of Arizona Agricultural Farm in Tucson until October 2017, and is now being permanently relocated to Big Bear Solar Observatory in California.