Hubble Deep Field

An image assembled from long Hubble Space Telescope exposures of a small, apparently empty region of sky, revealing thousands of distant galaxies.

Hubble Space Telescope: A space observatory launched in 1990, designed to observe the universe above Earth's atmosphere. Its stable orbit and sensitive instruments gathered the exposures that compose the image.
Robert Williams (astronomer): An American astronomer who served as director of the Space Telescope Science Institute from 1993 to 1998. He allocated director's discretionary time to the deep-field observation and helped shape its public release.
Galaxy formation and evolution: The processes by which galaxies form, grow, change structure, and cease forming stars over cosmic time. The image's range of galaxy ages and shapes offers evidence about how galaxies changed.
Hubble Ultra Deep Field: A 2004 Hubble image combining extensive exposures of a small region in the southern constellation Fornax. It pushed the deep-field strategy to fainter sources and greater distances.
Charge-coupled device: A semiconductor image sensor that converts incoming light into electrical charge for measurement. Hubble's cameras accumulated faint galaxy light on these sensors across repeated exposures.
Hubble Deep Field observing campaign: The 1995 Hubble program that repeatedly imaged a tiny northern-sky field over ten days. This campaign produced the exposures combined into the original Hubble Deep Field.
Galaxy luminosity function: A statistical description of how many galaxies occur at each intrinsic luminosity. Counts from the field helped constrain the abundance of faint galaxies.
Hubble eXtreme Deep Field: A 2012 image assembled from ten years of Hubble observations within the Ultra Deep Field. It reused the same sky region to reach still greater depth.
Exposure time: The duration for which a camera sensor collects light to form an image. Many hours of exposure let extremely faint sources rise above image noise.
Hubble Space Telescope Wide Field and Planetary Camera 2: A Hubble instrument that recorded images across ultraviolet, visible, and near-infrared bands. Its observations in four filters supplied the original field's multicolor data.

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