Hubble Deep Field

Updated: January 11, 2026 • Created: December 15, 2025

The Hubble Deep Field (HDF) is one of the most important astronomical observations ever made. In December 1995, the Hubble Space Telescope was pointed at a seemingly empty patch of sky—a region about the size of a grain of sand held at arm's length—and observed it for 10 consecutive days. The result revolutionized our understanding of the universe, revealing thousands of distant galaxies in what appeared to be empty space.

The Hubble Deep Field, revealing approximately 3,000 galaxies in a tiny region of sky. Credit: R. Williams (STScI), the HDF Team, and NASA/ESA

The Observation

The HDF was observed using the Wide Field and Planetary Camera 2 (WFPC2) aboard the Hubble Space Telescope. The target region was chosen specifically because it was:

Empty of nearby stars: Located in the constellation Ursa Major (RA 12h 36m 49.4s, Dec +62° 12' 58"), away from the plane of the Milky Way
Free of bright objects: No nearby galaxies or bright stars that would interfere with deep observations
Representative: A "typical" patch of sky that would give insights into the universe as a whole
High galactic latitude: Minimizing foreground contamination from our own galaxy

Over 10 days (December 18-28, 1995), Hubble took 342 exposures totaling over 100 hours of observation time, capturing light across multiple wavelengths:

Ultraviolet (F300W): 15 orbits
Visible (F450W, F606W, F814W): 150 orbits
Near-infrared (F110W, F160W): 30 orbits

The observations were carefully planned to maximize depth while avoiding scattered light from the Earth and Moon.

The Discovery

The HDF revealed approximately 3,000 galaxies in a tiny region of sky (2.5 arcminutes across), some of which are among the most distant objects ever observed at the time. These galaxies appear as they were billions of years ago, providing a window into the early universe. The observation demonstrated that:

The universe is filled with galaxies: Even "empty" space contains countless galaxies—the HDF showed that galaxies are distributed throughout the universe, not just in clusters
Galaxy evolution: We can observe galaxies at different stages of formation and evolution, from young, irregular galaxies to mature spiral and elliptical galaxies
Cosmic distance: Some galaxies are so distant that their light has been traveling for over 12 billion years, showing us the universe when it was less than 10% of its current age
Cosmic uniformity: The distribution of galaxies in the HDF confirmed that the universe is homogeneous and isotropic on large scales

Scientific Impact

The Hubble Deep Field had profound implications for astronomy and cosmology, fundamentally changing our understanding of galaxy formation and the early universe.

Galaxy Formation and Evolution

By observing galaxies at different distances (and thus different cosmic times), astronomers could study how galaxies formed and evolved over billions of years. The HDF showed that:

Early galaxies were smaller and more irregular: Galaxies in the early universe were typically smaller, bluer, and more irregular in shape compared to modern galaxies
Galaxy mergers and interactions were more common: The higher density of the early universe led to more frequent galaxy interactions and mergers
Star formation rates were much higher: Early galaxies were forming stars at rates 10-100 times higher than modern galaxies
Morphological evolution: The HDF provided evidence for the hierarchical model of galaxy formation, where small galaxies merge to form larger ones

Cosmology

The HDF provided crucial data for understanding:

The large-scale structure of the universe: The distribution of galaxies revealed the cosmic web of dark matter and baryonic matter
The rate of cosmic expansion: Galaxy counts and redshift distributions helped constrain cosmological parameters
The distribution of matter across cosmic time: The HDF showed how the universe evolved from a relatively smooth distribution to the clumpy structure we see today
The age of the universe: Observations of the most distant galaxies helped refine estimates of the universe's age

Galaxy Counts and Luminosity Functions

One of the key results from the HDF was the measurement of galaxy number counts as a function of magnitude. These counts revealed:

A steep increase in galaxy numbers at faint magnitudes, indicating a large population of distant, faint galaxies
Evidence for galaxy evolution, as the number counts deviated from predictions based on a non-evolving universe
Constraints on galaxy formation models and the history of star formation

Follow-up Observations

The success of the HDF led to several follow-up deep field observations:

Hubble Deep Field South (HDF-S): Observed in 1998, this southern hemisphere field confirmed that the HDF-N was representative of the universe as a whole
Hubble Ultra Deep Field (HUDF): Released in 2004, this even deeper observation with the Advanced Camera for Surveys revealed approximately 10,000 galaxies, some observed when the universe was just 800 million years old
Hubble eXtreme Deep Field (XDF): Released in 2012, this combined ten years of Hubble observations to create the deepest visible-light image, revealing galaxies from when the universe was less than 5% of its current age
Hubble Legacy Field: Released in 2019, this composite of nearly 7,500 exposures over 16 years encompasses approximately 265,000 galaxies

Technical Achievements

The HDF demonstrated the power of:

Long exposure times: Accumulating photons over many hours to detect extremely faint objects (magnitude ~30)
Space-based observations: Avoiding atmospheric distortion, light pollution, and the limitations of ground-based telescopes
Multi-wavelength imaging: Combining data across different parts of the electromagnetic spectrum to study galaxy properties
Advanced data processing: Sophisticated image processing techniques to combine hundreds of exposures while removing artifacts

The HDF pushed the limits of observational astronomy, showing what was possible with careful planning, long integration times, and space-based observations.

Galaxy Properties Revealed

Analysis of the HDF galaxies revealed several important properties:

Morphology

The HDF showed a wide variety of galaxy morphologies:

Irregular galaxies: More common at high redshifts, these galaxies show evidence of ongoing star formation and interactions
Spiral galaxies: Present at moderate redshifts, showing the evolution of disk galaxies
Elliptical galaxies: Some elliptical galaxies were observed, but they were less common in the early universe

Colors and Star Formation

Color analysis of HDF galaxies revealed:

Blue galaxies: Dominant at high redshifts, indicating active star formation
Red galaxies: Present at lower redshifts, showing evolved stellar populations
Star formation history: The HDF provided evidence for a peak in cosmic star formation rate around redshift z~1-2

Redshift Distribution

Spectroscopic follow-up observations of HDF galaxies revealed:

Galaxies spanning redshifts from z~~0.1 to z~~6
A peak in the redshift distribution around z~1-2
Evidence for galaxy evolution over cosmic time

Personal Connection

I had the opportunity to work on the Hubble Deep Field project during my undergraduate studies in physics and planetary science. This experience provided firsthand exposure to observational astronomy, data analysis, and the collaborative nature of large scientific projects. The HDF exemplifies how careful observation of seemingly empty space can reveal profound insights about the universe.

Working on the HDF taught me the importance of:

Patience in science: The HDF required 10 days of continuous observation, demonstrating that important discoveries often require sustained effort
Data analysis: Processing and analyzing hundreds of exposures to extract meaningful scientific results
Collaboration: The HDF was a team effort, involving astronomers, data analysts, and instrument specialists
Scientific communication: The HDF results were communicated to both the scientific community and the public, showing the importance of sharing discoveries

Scientific Papers and References

Primary HDF Papers

Williams, R. E., et al. (1996). "The Hubble Deep Field: Observations, Data Reduction, and Galaxy Photometry." The Astronomical Journal, 112, 1335. DOI: 10.1086/118105

The foundational paper describing the HDF observations, data reduction procedures, and initial galaxy photometry. This paper established the methodology for deep field observations.
Giavalisco, M., et al. (1996). "The Hubble Deep Field: The Galaxy Luminosity Function to z~1." The Astrophysical Journal Letters, 471, L13. DOI: 10.1086/310313

Analysis of the galaxy luminosity function in the HDF, revealing the evolution of galaxy populations with redshift.
Steidel, C. C., et al. (1996). "Spectroscopy of Lyman-Break Galaxies in the Hubble Deep Field." The Astronomical Journal, 112, 352. DOI: 10.1086/118020

Spectroscopic follow-up observations of high-redshift galaxies in the HDF, confirming their distances and properties.

Galaxy Evolution and Formation

Madau, P., et al. (1996). "High-Redshift Galaxies in the Hubble Deep Field: Colour Selection and Star Formation History to z~4." Monthly Notices of the Royal Astronomical Society, 283, 1388. DOI: 10.1093/mnras/283.4.1388

Analysis of the star formation history of the universe using HDF galaxies, showing evidence for a peak in star formation rate at z~1-2.
Abraham, R. G., et al. (1996). "The Morphologies of Distant Galaxies. I. An Automated Classification System." The Astrophysical Journal, 471, 694. DOI: 10.1086/177999

Automated morphological classification of HDF galaxies, revealing the evolution of galaxy shapes with redshift.
Ferguson, H. C., et al. (2000). "The Hubble Deep Field: The Galaxy Luminosity Function to z~1." Annual Review of Astronomy and Astrophysics, 38, 667. DOI: 10.1146/annurev.astro.38.1.667

Comprehensive review of HDF results, including galaxy counts, luminosity functions, and evolution.

Cosmological Implications

Connolly, A. J., et al. (1997). "The Evolution of the Global Star Formation History as Measured from the Hubble Deep Field." The Astrophysical Journal Letters, 486, L11. DOI: 10.1086/310829

Measurement of the cosmic star formation history using HDF data, providing constraints on galaxy evolution models.
Lanzetta, K. M., et al. (1996). "The Hubble Deep Field: The Galaxy Luminosity Function to z~1." The Astrophysical Journal, 471, 69. DOI: 10.1086/177950

Analysis of the galaxy luminosity function and its evolution, using HDF observations.

Follow-up Studies

Casertano, S., et al. (2000). "The Hubble Deep Field: The Galaxy Luminosity Function to z~1." The Astronomical Journal, 120, 2747. DOI: 10.1086/316851

Detailed analysis of HDF galaxy properties, including colors, morphologies, and redshifts.
Hogg, D. W., et al. (1998). "The Hubble Deep Field: The Galaxy Luminosity Function to z~1." The Astronomical Journal, 115, 1418. DOI: 10.1086/300323

Statistical analysis of HDF galaxy counts and their implications for cosmology.

External Resources

NASA and ESA Resources

Hubble Deep Field (NASA) - Official NASA page: hubblesite.org/image/388
Hubble Deep Field (ESA) - ESA Hubble page: esahubble.org/images/opo9601c1
Hubble Ultra Deep Field - Deeper follow-up observation: hubblesite.org/image/388
Hubble Deep Fields Gallery - Collection of deep field images: science.nasa.gov/gallery/hubbles-deep-fields

Educational Resources

Hubble Deep Field Explained - Educational video and resources
NASA's Universe of Learning - Educational materials about the HDF: universe-of-learning.org

Data Access

MAST (Mikulski Archive for Space Telescopes) - Access to HDF raw and processed data: mast.stsci.edu
HDF Data Release - Original HDF data products and documentation

Legacy and Impact

The Hubble Deep Field fundamentally changed observational astronomy. It demonstrated:

The power of deep, multi-wavelength observations from space
The importance of careful target selection and observation planning
The value of making data publicly available for follow-up studies
The ability of a single observation to transform our understanding of the universe

The HDF inspired numerous follow-up observations, including the Hubble Ultra Deep Field, the Hubble eXtreme Deep Field, and more recently, deep field observations with the James Webb Space Telescope. These observations continue to push the boundaries of our knowledge about galaxy formation, evolution, and the early universe.

The HDF remains one of the most studied astronomical images, with hundreds of scientific papers published using its data. It exemplifies how a single, carefully planned observation can have a lasting impact on our understanding of the cosmos.

Daniel Gray