Hubble Ultra-Deep Field

An image assembled from long Hubble Space Telescope observations of a small sky region, revealing thousands of galaxies across a wide range of cosmic distances.

Hubble Space Telescope: A space observatory launched in 1990 that observes the universe across ultraviolet, visible, and near-infrared wavelengths. Its repeated exposures supplied the observations assembled into the field.
HUDF09: A 2009 Hubble observing program that added deep near-infrared exposures to the Ultra-Deep Field region. Its exposures extended the field’s view toward highly redshifted early galaxies.
Galaxy formation and evolution: The processes by which galaxies assemble, change their structure, and evolve across cosmic history. The field provides observations of galaxies at many stages of cosmic history.
Observable universe: The region of the universe from which light has had time to reach Earth since the beginning of cosmic expansion. The field samples only a tiny direction within this vast region.
Long-exposure photography: A photographic technique that gathers light over an extended interval to record faint or dim objects. Thousands of seconds of exposure brought extremely faint galaxies into view.
HUDF12: A 2012 Hubble program that obtained deeper near-infrared observations of the Ultra-Deep Field. It added infrared data that sharpened searches for very distant galaxies.
Galaxy luminosity function: A statistical description of how many galaxies occur at each luminosity in a given volume or population. Counting faint sources helps constrain how galaxy numbers vary with brightness and distance.
Cosmological principle: The assumption that the universe is homogeneous and isotropic on sufficiently large scales. Deep-field comparisons test whether galaxy populations differ substantially between sky regions.
Drizzle algorithm: An image-reconstruction method that combines undersampled astronomical exposures while preserving spatial resolution. It helped combine dithered Hubble exposures into a sharp composite.
XDF: The eXtreme Deep Field, a composite of Hubble observations covering a small region within the Ultra-Deep Field. It combined observations across nearly a decade to reach fainter sources.

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AstrophotographyBroader topic: It demonstrates how prolonged imaging reveals galaxies too faint for ordinary exposures.