Sloan Digital Sky Survey

The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project was named after the Alfred P. Sloan Foundation, which contributed significant funding.

Data collection began in 2000;[1] the final imaging data release (DR9) covers over 35% of the sky, with photometric observations of around nearly 1 billion objects, while the survey continues to acquire spectra, having so far taken spectra of over 4 million objects. The main galaxy sample has a median redshift of z = 0.1; there are redshifts for luminous red galaxies as far as z = 0.7, and for quasars as far as z = 5; and the imaging survey has been involved in the detection of quasars beyond a redshift z = 6.

Data release 8 (DR8), released in January 2011,[2] includes all photometric observations taken with the SDSS imaging camera, covering 14,555 square degrees on the sky (just over 35% of the full sky). Data release 9 (DR9), released to the public on 31 July 2012,[3] includes the first results from the Baryon Oscillation Spectroscopic Survey (BOSS) spectrograph, including over 800,000 new spectra. Over 500,000 of the new spectra are of objects in the Universe 7 billion years ago (roughly half the age of the universe).[4] Data release 10 (DR10), released to the public on 31 July 2013,[5] includes all data from previous releases, plus the first results from the APO Galactic Evolution Experiment (APOGEE) spectrograph, including over 57,000 high-resolution infrared spectra of stars in the Milky Way. DR10 also includes over 670,000 new BOSS spectra of galaxies and quasars in the distant universe. The publicly available images from the survey were made between 1998 and 2009.

Sloan Digital Sky Survey
Alternative namesSDSS
Observatory code645
Websitewww.sdss.org

Observations

SDSS uses a dedicated 2.5 m wide-angle optical telescope; from 1998 to 2009 it observed in both imaging and spectroscopic modes. The imaging camera was retired in late 2009, since then the telescope has observed entirely in spectroscopic mode.

Images were taken using a photometric system of five filters (named u, g, r, i and z). These images are processed to produce lists of objects observed and various parameters, such as whether they seem pointlike or extended (as a galaxy might) and how the brightness on the CCDs relates to various kinds of astronomical magnitude.

For imaging observations, the SDSS telescope used the drift scanning technique, which tracks the telescope along a great circle on the sky and continuously records small strips of the sky.[6] The image of the stars in the focal plane drifts along the CCD chip, and the charge is electronically shifted along the detectors at exactly the same rate, instead of staying fixed as in tracked telescopes. (Simply parking the telescope as the sky moves is only workable on the celestial equator, since stars at different declination move at different apparent speed). This method allows consistent astrometry over the widest possible field, and minimises overheads from reading out the detectors. The disadvantage is minor distortion effects.

The telescope's imaging camera is made up of 30 CCD chips, each with a resolution of 2048×2048 pixels, totaling approximately 120 megapixels.[7] The chips are arranged in 5 rows of 6 chips. Each row has a different optical filter with average wavelengths of 355.1, 468.6, 616.5, 748.1 and 893.1 nm, with 95% completeness in typical seeing to magnitudes of 22.0, 22.2, 22.2, 21.3, and 20.5, for u, g, r, i, z respectively.[8] The filters are placed on the camera in the order r, i, u, z, g. To reduce noise, the camera is cooled to 190 kelvins (about −80 °C) by liquid nitrogen.

Using these photometric data, stars, galaxies, and quasars are also selected for spectroscopy. The spectrograph operates by feeding an individual optical fibre for each target through a hole drilled in an aluminum plate.[9] Each hole is positioned specifically for a selected target, so every field in which spectra are to be acquired requires a unique plate. The original spectrograph attached to the telescope was capable of recording 640 spectra simultaneously, while the updated spectrograph for SDSS III can record 1000 spectra at once. Over the course of each night, between six and nine plates are typically used for recording spectra. In spectroscopic mode, the telescope tracks the sky in the standard way, keeping the objects focused on their corresponding fibre tips.

Every night the telescope produces about 200 GB of data.

SDSS spectrograph cartridge
SDSS spectroscope cartridge
SDSS spectrograph plate
Aluminum plate close up showing optical fibers

Phases

Quasars Acting as Gravitational Lenses
Quasars acting as gravitational lenses. To find these cases of galaxy–quasar combinations acting as lenses, astronomers selected 23,000 quasar spectra from the SDSS.[10]

SDSS-I: 2000–2005

During its first phase of operations, 2000–2005, the SDSS imaged more than 8,000 square degrees of the sky in five optical bandpasses, and it obtained spectra of galaxies and quasars selected from 5,700 square degrees of that imaging. It also obtained repeated imaging (roughly 30 scans) of a 300 square degree stripe in the southern Galactic cap.

SDSS-II: 2005–2008

In 2005 the survey entered a new phase, the SDSS-II, by extending the observations to explore the structure and stellar makeup of the Milky Way, the SEGUE and the Sloan Supernova Survey, which watches after supernova Ia events to measure the distances to far objects.

Sloan Legacy Survey

The survey covers over 7,500 square degrees of the Northern Galactic Cap with data from nearly 2 million objects and spectra from over 800,000 galaxies and 100,000 quasars. The information on the position and distance of the objects has allowed the large-scale structure of the Universe, with its voids and filaments, to be investigated for the first time. Almost all of these data were obtained in SDSS-I, but a small part of the footprint was finished in SDSS-II.[11]

Sloan Extension for Galactic Understanding and Exploration (SEGUE)

The Sloan Extension for Galactic Understanding and Exploration obtained spectra of 240,000 stars (with typical radial velocity of 10 km/s) in order to create a detailed three-dimensional map of the Milky Way.[12] SEGUE data provide evidence for the age, composition and phase space distribution of stars within the various Galactic components, providing crucial clues for understanding the structure, formation and evolution of our galaxy.
The stellar spectra, imaging data, and derived parameter catalogs for this survey are publicly available as part of SDSS Data Release 7 (DR7).[13]

Sloan Supernova Survey

Running until the end of the year 2007, the Supernova Survey searched for Type Ia supernovae. The survey rapidly scanned a 300 square degree area to detect variable objects and supernovae. It detected 130 confirmed supernovae Ia events in 2005 and a further 197 in 2006.[14] In 2014 an even larger catalogue was released containing 10,258 variable and transient sources. Of these, 4,607 sources are either confirmed or likely supernovae, which makes this the largest set of supernovae so far compiled.[15]

SDSS III: 2008–2014

In mid-2008, SDSS-III was started. It comprises four separate surveys:[16]

APO Galactic Evolution Experiment (APOGEE)

The APO Galactic Evolution Experiment (APOGEE) will use high-resolution, high signal-to-noise infrared spectroscopy to penetrate the dust that obscures the inner Galaxy.[17] APOGEE will survey 100,000 red giant stars across the full range of the galactic bulge, bar, disk, and halo. APOGEE will increase the number of stars observed at high spectroscopic resolution (R ~ 20,000 at λ ~ 1.6μm) and high signal-to-noise ratio (S/N ~ 100) by more than a factor of 100.[18] The high resolution spectra will reveal the abundances of about 15 elements which gives information on the composition of the gas clouds they formed from. APOGEE should be collecting data from 2011 to 2014 with first release of data in July 2013.

Baryon Oscillation Spectroscopic Survey (BOSS)

The SDSS-III's Baryon Oscillation Spectroscopic Survey (BOSS) was designed to measure the expansion rate of the Universe.[19] It will map the spatial distribution of luminous red galaxies (LRGs) and quasars to map the spatial distribution and detect the characteristic scale imprinted by baryon acoustic oscillations in the early universe. Sound waves that propagate in the early universe, like spreading ripples in a pond, imprint a characteristic scale on the positions of galaxies relative to each other. It was announced that BOSS had measured the scale of the universe to an accuracy of one percent, and was completed in Spring 2014.[20]

Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS)

The Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS) will monitor the radial velocities of 11,000 bright stars, with the precision and cadence needed to detect gas giant planets that have orbital periods ranging from several hours to two years. This ground-based Doppler survey [21] will use the SDSS telescope and new multi-object Doppler instruments to monitor radial velocities.[21] It is one of four astronomical surveys conducted by SDSS-III, part of the Sloan Digital Sky Survey (SDSS).
The main goal of the project is to generate a large-scale, statistically well-defined sample of giant planets. It will search for gaseous planets that have orbital periods ranging from hours to 2 years, and are between 0.5 and 10 Jupiter masses. A total of 11,000 stars will be analyzed with 25-35 observations per star over an 18-month period. It is expected to detect between 150 and 200 new exoplanets, and will be able to study rare systems, such as planets with extreme eccentricity, and objects in the "brown dwarf desert".[21][22]
The collected data will be used as a statistical sample for the theoretical comparison and discovery of rare systems.[23] The project started in the fall of 2008, and continued until spring 2014.[21][24]

SEGUE-2

The original Sloan Extension for Galactic Understanding and Exploration (SEGUE-1) obtained spectra of nearly 240,000 stars of a range of spectral types. Building on this success, SEGUE-2 spectroscopically observed around 120,000 stars, focusing on the in situ stellar halo of the Galaxy, from distances of 10 to 60 kpc.
Combining SEGUE-1 and 2 reveals the complex kinematic and chemical substructure of the Galactic halo and disks, providing essential clues to the assembly and enrichment history of the Galaxy. In particular, the outer halo is expected to be dominated by late-time accretion events. SEGUE can help constrain existing models for the formation of the stellar halo and inform the next generation of high resolution simulations of Galaxy formation. In addition, SEGUE-1 and SEGUE-2 help uncover rare, chemically primitive stars that are fossils of the earliest generations of cosmic star formation.
It is an astronomical survey designed to map the outer reaches of the Milky Way with a spectra of 240,000 stars. This survey will double the sample size of SEGUE-1.[25]

SDSS IV: 2014–2020

Monster in the deep
Light from distant galaxies has been smeared and twisted into odd shapes, arcs, and streaks.[26]

The latest generation of the SDSS (SDSS-IV, 2014–2020) is extending precision cosmological measurements to a critical early phase of cosmic history (eBOSS), expanding its infrared spectroscopic survey of the Galaxy in the northern and southern hemispheres (APOGEE-2), and for the first time using the Sloan spectrographs to make spatially resolved maps of individual galaxies (MaNGA).[27]

APO Galactic Evolution Experiment (APOGEE-2)

A stellar survey of the Milky Way, with two major components: a northern survey using the bright time at APO, and a southern survey using the 2.5m du Pont Telescope at Las Campanas.

extended Baryon Oscillation Spectroscopic Survey (eBOSS)

A cosmological survey of quasars and galaxies, also encompassing subprograms to survey variable objects (TDSS) and X-Ray sources (SPIDERS).

Mapping Nearby Galaxies at APO (MaNGA)

Hdp middenvlak
A simplified graphical representation of the bundled fiber optical wires used to obtain data from MaNGA data.
MaNGA (Mapping Nearby Galaxies at Apache Point Observatory), has been exploring the detailed internal structure of nearly 10,000 nearby galaxies since 2014. Earlier SDSS surveys only allowed spectra to be observed from the center of galaxies. By using a two-dimensional array of optical fibers bundled together into a hexagonal shape, MaNGA will be able to use spatially resolved spectroscopy to construct maps of the areas within galaxies, allowing deeper analysis of their structure, such as radial velocities and star formation regions.[28] The hope of MaNGA is to enable further studies of astrophysics in nearby galaxies, with the project expected to continue until 2020.[29]
Hdp middenvlak
A simplified graphical representation of the bundled fiber optical wires used to obtain data from MaNGA data.

Data access

LRG-4-606
LRG-4-606 is a Luminous Red Galaxy. LRG is the acronym given to a catalog of bright red galaxies found in the SDSS.

The survey makes the data releases available over the Internet. The SkyServer provides a range of interfaces to an underlying Microsoft SQL Server. Both spectra and images are available in this way, and interfaces are made very easy to use so that, for example, a full color image of any region of the sky covered by an SDSS data release can be obtained just by providing the coordinates. The data are available for non-commercial use only, without written permission. The SkyServer also provides a range of tutorials aimed at everyone from schoolchildren up to professional astronomers. The tenth major data release, DR10, released in July 2013,[5] provides images, imaging catalogs, spectra, and redshifts via a variety of search interfaces.

The raw data (from before being processed into databases of objects) are also available through another Internet server, and first experienced as a 'fly-through' via the NASA World Wind program.

Sky in Google Earth includes data from the SDSS, for those regions where such data are available. There are also KML plugins for SDSS photometry and spectroscopy layers,[30] allowing direct access to SkyServer data from within Google Sky.

The data is also available on Hayden Planetarium with a 3D visualizer.

There is also the ever-growing list of data for the Stripe 82 region of the SDSS.

Following from Technical Fellow Jim Gray's contribution on behalf of Microsoft Research with the SkyServer project, Microsoft's WorldWide Telescope makes use of SDSS and other data sources.[31]

MilkyWay@home also used SDSS's data for creating a highly accurate three dimensional model of the Milky Way galaxy.

Results

Along with publications describing the survey itself, SDSS data have been used in publications over a huge range of astronomical topics. The SDSS website has a full list of these publications covering distant quasars at the limits of the observable universe,[32] the distribution of galaxies, the properties of stars in our own galaxy and also subjects such as dark matter and dark energy in the universe.

Maps

Based on the release of Data Release 9 a new 3D map of massive galaxies and distant black holes was published on August 8, 2012.[33]

See also

References

  1. ^ Gunn, James E.; Siegmund, Walter A.; Mannery, Edward J.; Owen, Russell E.; Hull, Charles L.; Leger, R. French; et al. (April 2006). "The 2.5 m Telescope of the Sloan Digital Sky Survey". The Astronomical Journal. 131 (4): 2332–2359. arXiv:astro-ph/0602326. Bibcode:2006AJ....131.2332G. doi:10.1086/500975.
  2. ^ "SDSS Data Release 8". sdss3.org. Retrieved 2011-01-10.
  3. ^ "SDSS Data Release 9". sdss3.org. Retrieved 2012-07-31.
  4. ^ "New 3D Map of Massive Galaxies and Black Holes Offers Clues to Dark Matter, Dark Energy" (Press release). New York University. 8 August 2012.
  5. ^ a b "SDSS Data Release 10". sdss3.org. Retrieved 2013-08-04.
  6. ^ David Rabinowitz (2005). "Drift Scanning (Time-Delay Integration)" (PDF). Retrieved 2006-12-27.
  7. ^ "Key Components of the Survey Telescope". SDSS. 2006-08-29. Archived from the original on 2007-01-07. Retrieved 2006-12-27.
  8. ^ "SDSS Data Release 7 Summary". SDSS. 2011-03-17.
  9. ^ Newman, Peter R.; et al. (2004). "Mass-producing spectra: the SDSS spectrographic system". Proc. SPIE. 5492: 533. arXiv:astro-ph/0408167. doi:10.1117/12.541394. Retrieved 3 December 2012.
  10. ^ "Quasars Acting as Gravitational Lenses". ESA/Hubble Picture of the Week. Retrieved 19 March 2012.
  11. ^ "About the SDSS Legacy Survey".
  12. ^ "Sloan Extension for Galactic Understanding and Exploration". segue.uchicago.edu. Archived from the original on 2008-02-19. Retrieved 2008-02-27.
  13. ^ Yanny, Brian; Rockosi, Constance; Newberg, Heidi Jo; Knapp, Gillian R.; et al. (1 May 2009). "SEGUE: A Spectroscopic Survey of 240,000 Stars with g = 14-20". The Astronomical Journal. 137 (5): 4377–4399. arXiv:0902.1781. Bibcode:2009AJ....137.4377Y. doi:10.1088/0004-6256/137/5/4377.
  14. ^ Sako, Masao; et al. (2008). "The Sloan Digital Sky Survey-II Supernova Survey: search algorithm and follow-up observations". Astronomical Journal. 135 (1): 348–373. arXiv:0708.2750. Bibcode:2008AJ....135..348S. doi:10.1088/0004-6256/135/1/348.
  15. ^ Sako, Masao; et al. (2014). "The Data Release of the Sloan Digital Sky Survey-II Supernova Survey". arXiv:1401.3317.
  16. ^ http://www.sdss3.org/surveys/
  17. ^ "Sdss-III". Sdss3.org. Retrieved 2011-08-14.
  18. ^ "SDSS-III: Massive Spectroscopic Surveys of the Distant Universe, the Milky Way Galaxy, and Extra-Solar Planetary Systems" (PDF). Jan 2008. pp. 29–40.
  19. ^ "BOSS: Dark Energy and the Geometry of Space". SDSS III. Retrieved 26 September 2011.
  20. ^ https://www.sdss3.org/surveys/boss.php
  21. ^ a b c d "Sdss-III". Sdss3.org. Retrieved 2011-08-14.
  22. ^ Publicado por Fran Sevilla. "Carnival of Space #192: Exoplanet discovery and characterization". Vega 0.0. Archived from the original on 2011-04-23. Retrieved 2011-08-14.
  23. ^ "The Multi-Object APO Radial-Velocity Exoplanet Large-area Survey (MARVELS)". aspbooks.org. Retrieved 2011-08-14.
  24. ^ Matt Rings (2011-01-23). "Collaboration results in largest-ever image of the night-time sky". Gizmag.com. Retrieved 2011-08-14.
  25. ^ "Sdss-III". Sdss3.org. Retrieved 2011-08-14.
  26. ^ "Monster in the deep". www.spacetelescope.org. Retrieved 30 April 2018.
  27. ^ http://www.sdss.org/surveys/
  28. ^ "MaNGA | SDSS". www.sdss.org. Retrieved 2017-04-18.
  29. ^ Bundy, Kevin; Bershady, Matthew A.; Law, David R.; Yan, Renbin; Drory, Niv; MacDonald, Nicholas; Wake, David A.; Cherinka, Brian; Sánchez-Gallego, José R. (2015-01-01). "Overview of the SDSS-IV MaNGA Survey: Mapping nearby Galaxies at Apache Point Observatory". The Astrophysical Journal. 798 (1): 7. arXiv:1412.1482. Bibcode:2015ApJ...798....7B. doi:10.1088/0004-637X/798/1/7. ISSN 0004-637X.
  30. ^ "Google Earth KML: SDSS layer". earth.google.com. Archived from the original on 2008-03-17. Retrieved 2008-03-24.
  31. ^ "When did Microsoft first starting looking at the sky?". worldwidetelescope.org. Archived from the original on 2008-03-02. Retrieved 2008-03-24.
  32. ^ "SDSS Scientific and Technical Publications". sdss.org. Archived from the original on 2008-02-17. Retrieved 2008-02-27.
  33. ^ "SDSS Science Results". sdss3.org. Retrieved 2012-08-08.

Further reading

  • Ann K. Finkbeiner. A Grand and Bold Thing: An Extraordinary New Map of the Universe Ushering In A New Era of Discovery (2010), a journalistic history of the project

External links

(472271) 2014 UM33

(472271) 2014 UM33, provisionally designated 2010 TQ182, is a trans-Neptunian object and possible dwarf planet residing in the outer Kuiper belt. It was discovered on October 22, 2014, by the Mount Lemmon Survey. Its orbit was initially poorly determined, with 17 observations over 62 days, giving it an orbital uncertainty of 8. It is listed on Mike Brown's website as a probable dwarf planet, ranked 67th most likely.It is approximately the size of 2 Pallas in the asteroid belt. On August 18, 2015, 2014 UM33 was found to have been discovered over four years previously, with the designation 2010 TQ182. This extended its observation arc to over 4 years, and then precovery observations were found using the Sloan Digital Sky Survey from 2009.

2006 RJ103

2006 RJ103 is a Neptune trojan, first observed by the Sloan Digital Sky Survey Collaboration at Apache Point Observatory, New Mexico, on 12 September 2006. It was the fifth and largest such body discovered, approximately 180 kilometers in diameter. As of 2016, it is 30.3 AU from Neptune.

311P/PANSTARRS

311P/PANSTARRS also known as P/2013 P5 (PANSTARRS) is an asteroid (or main-belt comet) discovered by the Pan-STARRS telescope on 27 August 2013. Observations made by the Hubble Space Telescope revealed that it had six comet-like tails. The tails are suspected to be streams of material ejected by the asteroid as a result of a rubble pile asteroid spinning fast enough to remove material from it. This is similar to 331P/Gibbs, which was found to be a quickly-spinning rubble pile as well.

Three-dimensional models constructed by Jessica Agarwal of the Max Planck Institute for Solar System Research in Lindau, Germany, showed that the tails could have formed by a series of periodic impulsive dust-ejection events, radiation pressure from the sun then stretched the dust into streams.Precovery images from the Sloan Digital Sky Survey from 2005 were found, showing negligible cometary activity in 2005.

6dF Galaxy Survey

The 6dF Galaxy Survey (Six-degree Field Galaxy Survey), 6dF or 6dFGS is a redshift survey conducted by the Anglo-Australian Observatory (AAO) with the 1.2m UK Schmidt Telescope between 2001 and 2009. The data from this survey were made public on 31 March, 2009. The survey has mapped the nearby universe over nearly half the sky. Its 136,304 spectra have yielded 110,256 new extragalactic redshifts and a new catalog of 125,071 galaxies. For a subsample of 6dF a peculiar velocity survey is measuring mass distribution and bulk motions of the local Universe. As of July 2009, it is the third largest redshift survey next to the Sloan Digital Sky Survey (SDSS) and the 2dF Galaxy Redshift Survey (2dFGRS).

Andromeda IX

Andromeda IX (And 9) is a dwarf spheroidal satellite of the Andromeda Galaxy. It was discovered in 2004 by resolved stellar photometry from the Sloan Digital Sky Survey (SDSS), by Zucker et al. (2004). At the time of its discovery, it was the galaxy with the lowest known surface brightness, ΣV ≃ 26.8mags arcsec−2 and the faintest galaxy known from its intrinsic absolute brightness.It was found from data acquired within an SDSS scan along the major axis of M31, on October 5, 2002. Its distance was estimated to be almost exactly the same as that of M31 by McConnacrchie et al. (2005).

DEEP2 Redshift Survey

The DEEP2 Survey or DEEP2 was a two-phased Redshift survey of the Redshift z=~1 universe (where z= a measure of speed and by extension, the distance from earth). It used the twin 10 metre Keck telescopes in Hawaii (the world's second largest optical telescope) to measure the spectra and hence the redshifts of approximately 50,000 galaxies. It was the first project to study galaxies in the distant Universe with the resolution of local surveys like the Sloan Digital Sky Survey and was completed in 2013.

GALEX Arecibo SDSS Survey

GALEX Arecibo SDSS Survey (GASS) is a large targeted survey at Arecibo Observatory that has been underway since 2008 to measure the neutral hydrogen content of a representative sample of approximately 1000 massive galaxies selected using the Sloan Digital Sky Survey and GALEX imaging surveys. The telescope being used is the world's largest single-dish radio telescope and can receive signals from distant objects.

Galaxy color–magnitude diagram

The galaxy color–magnitude diagram shows the relationship between absolute magnitude (a measure of luminosity) and mass of galaxies. A preliminary description of the three areas of this diagram was made in 2003 by Eric F. Bell et al. from the COMBO-17 survey that clarified the bimodal distribution of red and blue galaxies as seen in analysis of Sloan Digital Sky Survey data and even in de Vaucouleurs' 1961 analyses of galaxy morphology.The diagram has three main features: the red sequence, the green valley, and the blue cloud. The red sequence includes most red galaxies, which are generally elliptical galaxies. The blue cloud includes most blue galaxies, which are generally spirals. In between the two distributions is an underpopulated space known as the green valley which includes a number of red spirals.

Unlike the comparable Hertzsprung–Russell diagram for stars, galaxy properties are not necessarily completely determined by their location on the color–magnitude diagram. The diagram also shows considerable evolution through time. The red sequence earlier in evolution of the universe was more constant in color across magnitudes and the blue cloud was not as uniformly distributed but showed sequence progression.

New research suggests the green valley is actually composed of two different populations of galaxies: one of late-type galaxies, where star formation has been quenched due to their gas supplies being shut off followed by exhaustion of their gas reservoirs for several billion years, and another of early-type galaxies where both the gas supplies and gas reservoirs have been destroyed very quickly, likely because of mergers with other galaxies and/or the presence of an active galactic nucleus.The Milky Way and the Andromeda Galaxy are assumed to lie in the green valley because their star formation is slowing down due to running out of gas.

James E. Gunn (astronomer)

James Edward Gunn (born October 21, 1938) is the Eugene Higgins Professor of Astronomy at Princeton University. Gunn's early theoretical work in astronomy has helped establish the current understanding of how galaxies form, and the properties of the space between galaxies. He also suggested important observational tests to confirm the presence of dark matter in galaxies, and predicted the existence of a Gunn–Peterson trough in the spectra of distant quasars.

Much of Gunn's later work has involved leadership in major observational projects. He developed plans for one of the first uses of digital camera technology for space observation, a project that led to the Sloan Digital Sky Survey, the most extensive three-dimensional mapping of the universe ever undertaken. He also played a major role with the Wide Field and Planetary Camera on the Hubble Space Telescope.

Gunn earned his bachelor's degree at Rice University in Houston, Texas, in 1961, and his Ph.D. from the California Institute of Technology (Caltech) in 1965. He joined the faculty of Princeton University two years later. Subsequently, he worked at the University of California at Berkeley and Caltech before returning to Princeton. He is married to the astronomer Gillian Knapp and they have two children, Humberto and Marleny Gunn.

Monoceros Ring

The Monoceros Ring is a long, complex, ringlike filament of stars that wraps around the Milky Way three times. This is proposed to consist of a stellar stream torn from the Canis Major Dwarf Galaxy by tidal forces as part of the process of merging with the Milky Way over a period of billions of years, although this view has long been disputed. The ring contains 100 million solar masses and is 200,000 light years long.The stream of stars was first reported in 2002 by astronomers conducting the Sloan Digital Sky Survey. It was in the course of investigating this ring of stars, and a closely spaced group of globular clusters similar to those associated with the Sagittarius Dwarf Elliptical Galaxy, that the Canis Major Dwarf Galaxy was discovered.

Segue 3

Segue 3 is a faint star cluster of the Milky Way galaxy discovered in 2010 in the data obtained by Sloan Digital Sky Survey. It is located in the Pegasus constellation at the distance of about 17 kpc from the Sun and moves away from it with the velocity of 167.1 ± 1.5 km/s.Segue 3 is extremely faint—its visible absolute magnitude is estimated at −1.2 or even at about 0.0 ± 0.8, which means that the cluster is only 100 to 250 times brighter than the Sun. Its small radius—of about 2.1 pc—is typical for the galactic globular clusters. The cluster has a slightly flattened shape and shows some evidence of the tidal disruption.The metallicity of Segue's 3 stars is [Fe/H] ≈ −1.7, which means that they contain 70 times less heavy elements than the Sun. These stars are more than 12 billion year old. Segue 3 appears to be one of the faintest globular clusters of the Milky Way.

Sloan

Sloan may refer to:

Sloan (surname)

MIT Sloan School of Management at the Massachusetts Institute of Technology, United States

Sloan (band), a Canadian rock band

Sloan Digital Sky Survey, a major astronomical survey

Sloan Great Wall, a galactic filament discovered by the Sloan Digital Sky Survey

Sloan Fellowship, a research grant to young scientists and scholars

Sloan Research Fellowship, a mid-career master's degree program in general management

Sloan Valve Company, a manufacturer of plumbing systems

Urania sloanus or Sloan's urania, a species of moth

Alfred P. Sloan Foundation, a large philanthropic organization

Sloan Great Wall

The Sloan Great Wall (SGW) is a cosmic structure formed by a giant wall of galaxies (a galaxy filament). Its discovery was announced from Princeton University on October 20, 2003, by J. Richard Gott III, Mario Jurić, and their colleagues, based on data from the Sloan Digital Sky Survey.

Stephanie Snedden

Stephanie A. Snedden is a researcher in space science at Apache Point Observatory, New Mexico State University in the US. The minor planet 133008 Snedden 2002 is named after her; it was discovered by the Sloan Digital Sky Survey at Apache Point Observatory on 5 October 2002. She has published papers including The Case for Optically Thick High-Velocity Broad-Line Region Gas in Active Galactic Nuclei.

U1.11

U1.11 is a large quasar group located in the constellations of Leo and Virgo. It is one of the largest LQG's known, with the estimated maximum diameter of 780 Mpc (2.2 billion light-years) and contains 38 quasars. It was discovered in 2011 during the course of the Sloan Digital Sky Survey. Until the discovery of the Huge-LQG in November 2012, it was the largest known structure in the universe, beating Clowes–Campusano LQG's 20-year record as largest known structure at the time of its discovery.

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