The 7-Dimensional Sky Survey
7DS is the science program of 7DT. It comprises three surveys that differ in area, cadence and depth, and that share one tiling of the sky.
Three surveys on one tiling
7DS is the science program of 7DT. It comprises three surveys distinguished by area, cadence and depth: the Reference Imaging Survey (RIS), the Wide-area Time-domain Survey (WTS) and the Intensive Monitoring Survey (IMS). Across the three, area decreases and depth increases — from a single visit to the whole southern sky, to nightly observation of one field — while all three use the same instrument and the same tiling.
| Property | RIS | WTS | IMS |
|---|---|---|---|
| Survey area | 23,000 deg² | 800–1,200 deg² | 8.5 deg² |
| Target region | Dec < +20° | Fields with near-infrared ancillary data | AKARI / SPHEREx Deep Field South |
| Cadence | Single visit | 10–14 days | 1 day |
| Depth | 19.1 mag | 22.2 mag* | 23.6 mag* |
| Status | Observing | Commencing 2026 | Observing |
Depths are 5σ point-source limits in the m600 band. The RIS figure is the depth of one visit (3 × 100 s); the WTS and IMS figures are cumulative over the planned five-year operation. Measured performance is reported on the performance page, and current progress on each survey page.
One tile pattern for the whole program
All 7DS observations use a common set of fixed pointings, generated from a HEALPix pixelization of the celestial sphere. Adjacent pointings overlap by about 5 arcminutes in right ascension and 4 arcminutes in declination near the celestial equator, and by more toward the poles. Tiles are numbered T00000 to T28519 in order of increasing declination, covering everything accessible to the array from the south celestial pole to +30 degrees.
This tiling is the operational reference for the whole program. WTS and IMS point at the same tile centers, and target-of-opportunity observations use them wherever the field allows. Because all three surveys share it, data from any of them coadd directly with data from the others and difference imaging always runs against a consistent reference. A visit is three consecutive 100-second exposures coadded to a 300-second frame; the exposure length is set by the unguided tracking capability of the mount and the read noise of the detector.
| Tile centers | HEALPix pixelization of the celestial sphere |
|---|---|
| Tile numbering | T00000 – T28519, by increasing declination |
| Sky coverage | South celestial pole to Dec +30° |
| Overlap near equator | ≈ 5′ in right ascension, 4′ in declination |
| Standard visit | 3 × 100 s, coadded to 300 s |
| Field of view per tile | 1.34° × 0.90°, 1.25 deg² |
Why three surveys and not one
Area, cadence and depth cannot all be maximized from a fixed number of nights. Rather than adopt a single compromise, 7DS operates at three separate points in that trade, and ties them together by using one tiling for all three, so that data from any of them coadd directly with data from the others.
Reference Imaging Survey
Area over depth and cadence
Give every part of the southern sky a medium-band reference image, once.
ObservingWTSWide-area Time-domain Survey
Cadence over area
Follow what changes on timescales of weeks, and stack deep enough to reach faint galaxies.
Commencing 2026IMSIntensive Monitoring Survey
Depth and cadence over area
Catch variability within a single night, and build the deepest photometry 7DS will produce.
ObservingEach survey page carries its own strategy, sky map, coverage and current status.