Center for the Gravitational-wave Universe · Seoul National University

7-Dimensional Sky Survey

A medium-band survey of the southern sky, measuring a low-resolution spectrum for every source it observes and repeating the measurement over time. It is carried out with the 7-Dimensional Telescope, an array of twenty 50-cm telescopes in Chile.

01Right ascension02Declination03Distance04Radial velocity05Brightness06Wavelength07Time

Introduction

A survey that measures spectra, not colors

The 7-Dimensional Sky Survey (7DS) is a medium-band survey of the southern sky. It is carried out with the 7-Dimensional Telescope (7DT), an array of twenty 50-cm telescopes at El Sauce Observatory in Chile, built and operated by the Center for the Gravitational-wave Universe at Seoul National University. Each unit carries a share of a forty-filter medium-band set, so a single visit records a low-resolution spectrum of every source in 1.25 square degrees. As of now, sixteen units and thirty-five filters are in routine operation.

What is 7DS

The Sculptor Galaxy, NGC 253, scanned through the 7DT medium-band filter set — **NGC 253** The Sculptor Galaxy seen through successive medium bands from 400 to 875 nm — each frame a different slice of the spectrum.

Science

Broad science topics

A medium-band spectral energy distribution for every source in the field supports a wide range of science from one data product: how galaxies assemble and cease forming stars, where the heavy elements are produced, the expansion rate of the Universe, accretion onto black holes, the variability of young stars, and the composition of small solar-system bodies. 7DS was designed to identify gravitational-wave counterparts; the same images serve the rest.

Science program

Live data · Aug 20, 2026, 09:20 AM UTC15,579 tiles observed

7-Dimensional Sky Survey

Three surveys over the southern sky

7DS comprises three surveys that trade area against depth and cadence: a single-visit reference map of the southern sky, a time-domain survey on a 10-14 day cadence, and nightly monitoring of a deep field at the south ecliptic pole. All three use the same tiling of the sky, so their data coadd directly.

Explore the coverage map

RIS

Reference Imaging Survey

23,000 deg² · Single visit

60.9% observed WTS

Wide-area Time-domain Survey

800–1,200 deg² · 10–14 days

Commencing 2026 IMS

Intensive Monitoring Survey

8.5 deg² · 1 day

Observing

The facility

Twenty telescopes, one system

Twenty DeltaRho 500 units on direct-drive mounts, sixteen currently observing, one control computer per operational telescope, a scheduler that can interrupt the night and begin a follow-up exposure in under a minute, and a pipeline that reduces a 3,000-image night the same day. The array is built to observe a transient while it is still bright.

Telescope & site

20Telescopes in the array16 online

40Medium-band filters35 installed

30–70Spectral resolution R

1.25deg²Per pointing

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