Astronomical survey

An astronomical survey systematically covers a large area of sky, often with a uniform cadence and sensitivity, to create a catalog or atlas. Unlike pointed observations, surveys are designed to be unbiased and complete, allowing astronomers to study populations of objects, such as galaxies, stars, or asteroids, and to detect transient events. Surveys have driven major discoveries, including dark energy (via supernova surveys) and exoplanet demographics (via transit surveys).²

The first major surveys were photographic, such as the Palomar Observatory Sky Survey (POSS) in the 1950s, which mapped the northern sky on glass plates. Later, digitized versions like the Digitized Sky Survey made these data accessible. The advent of CCDs and large-format cameras enabled digital surveys like the Sloan Digital Sky Survey (SDSS), which began in 2000 and has produced multi-color images of over a third of the sky. More recent surveys, such as Pan-STARRS and the Dark Energy Survey, have pushed deeper and wider.³

Modern surveys operate across the electromagnetic spectrum, from radio (e.g., the Very Large Array Sky Survey) to X-ray (e.g., eROSITA). Time-domain surveys, like the Zwicky Transient Facility, repeatedly image the sky to find supernovae, asteroids, and other variable sources. The upcoming Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) will produce a 10-year time-lapse movie of the southern sky, generating enormous data volumes that require advanced machine-learning pipelines for classification.⁴

Surveys have also been conducted from the ground in narrow wavelength bands, such as the H-alpha surveys for star-forming regions, and from space in the ultraviolet (GALEX) and infrared (WISE). The Hipparcos mission was a survey of astrometry, while Gaia continues it with unprecedented precision. Surveys are not limited to stars and galaxies: the Catalina Sky Survey and Pan-STARRS are dedicated to near-Earth objects. Some surveys, like the 2MASS, have been used to map the Milky Way's structure, revealing the bar and spiral arms. The term 'survey' also applies to spectroscopic surveys, such as the LAMOST survey, which obtains spectra for millions of objects, enabling radial velocity and chemical abundance studies.⁵

Cadence

The frequency and timing of observations of the same sky area.

Transient

An astronomical object or event that appears or changes over time, such as a supernova.

Photometric survey

A survey that measures the brightness of objects in multiple wavelength bands.