## Mission Overview

### Sky Coverage (Galactic)

The Digitized Sky Survey (DSS) consists of 1" and 1.7"/pixel resolution scans of photographic plates of the sky taken by the Palomar and UK Schmidt telescope, each covering 6.5 x 6.5 degrees. One of the key products of the DSS is the Guide Star Catalog (GSC), which is currently used for HST Bright Object Protection and HST and JWST pointing. The Guide Star Catalog has since been enhanced by including sources and information from additional catalogs including GAIA, 2MASS, WISE, and others. This all-sky catalog will ultimately contains positions, proper motions, classifications, and magnitudes in multiple bandpasses for several billion objects.

### Capabilities

• GSC supports pointing and target acquisition for HST and JWST, as well as ground-based observatories
• DSS provides sky chart images suitable for target acquisition at many observatories

Refer to the Data Use Policy page for copyright information for the DSS and GSC.

### Digitized Sky Survey

The Digitized Sky Survey comprises a set of all-sky photographic surveys in E, V, J, R, and N bands conducted with the Palomar and UK Schmidt telescopes. The Catalogs and Surveys Branch (CASB) digitized the photographic plates to to create the Guide Star Catalog(s) and support HST observing programs but also as a service to the astronomical community. A table of the Sky Surveys used is provided below. Please read the Data Use pages for copyright information on the DSS surveys.

The 6.5-degree x 6.5-degree plates are scanned using a modified PDS microdensitometer to a pixel scale of about 1.7 arcseconds per pixel for the POSS-I, SERC, and Palomar Quick-V surveys, and to about 1.0 arcseconds per pixel for the POSS-II and SES surveys.

Images of any part of the sky may be extracted from the DSS, in either FITS, JPG or GIF format.

### Guide Star Catalog

The Catalogs and Surveys Branch of the Space Telescope Science Institute originally constructed the Guide Star Catalog (GSC) to support the pointing and target acquisition for the Hubble Space Telescope (HST). It has since been adopted for numerous other purposes, for example, observation planning, the preparation of finding charts, and the operation of ground-based telescopes, as well as future space telescopes like the James Webb Space Telescope (JWST) and WFIRST.

The original version of the Guide Star Catalog (GSC-I) was an all-sky catalog of positions and magnitudes for approximately 19 million stars and other objects in the sixth to fifteenth magnitude range. The GSC-I was primarily based on an all-sky, single-epoch collection of Schmidt plates. For centers at +6° and north, a 1982 epoch "Quick V" survey was obtained from the Palomar Observatory, while for southern fields, materials from the UK SERC J survey (epoch = 1975) and its equatorial extension (epoch = 1982) were used. See Table of Sky Surveys below for more information on the plates.

The Guide Star Catalog II (GSC-II) was an all-sky optical catalog based on 1" resolution scans of the photographic Sky Survey plates, at two epochs and three bandpasses, from the Palomar and UK Schmidt telescopes. This all-sky catalog contains positions, proper motions, classifications, and magnitudes in multiple bandpasses for almost a billion objects down to approximately Jpg=21, Fpg=20.

The most recent versions of GSC 2.4 have been updated to provide improved astrometric positions from the ESA GAIA satellite and add fainter objects from additional ground-based survey telescopes. The latest information on the GSC can be found here.

## List of DSS Surveys

Survey

Code

Epoch

Emulsion
+filter

Band

Mag

Dec. zones

N plates

pixels

GSC
1/2

DSS
1/2

DSS

POSS-I E

XE

1950-58

103aE

Epg

20.0

+90:-30

936

1.0/1.7"

2

1

STScI

POSS-I O

XO

1950-58

103aO

Opg

21.0

+90:-30

936

1.0"

2

2

STScI

Pal-QV

N

1983-85

+W12

Vpg

19.5

+90:+06

611

1.7"

1+2

2

STScI

POSS-II J

XJ

1987-98

IIIaJ
+GG395

Jpg

22.5

+90:+00

897

1.0"

2

2

Caltech

POSS-II F

XP

1987-98

IIIaF
+RG610

Fpg

20.8

+90:+00

897

1.0"

2

2

Caltech

POSS-II N

XI

1987-02

IV-N
+RG9

Ipg

19.5

+90:+00

890

1.0"

2

2

Caltech

SERC-J*

S

1975-87

IIIaJ
+GG395

Jpg

23.0

-20:-90

606

1.7"

1+2

1

ROE

SERC-EJ

S

1979-88

IIIaJ
+GG395

Jpg

23.0

-00:-15

288

1.7"

1+2

1

ROE

AAO-SES

XS

1990-98

IIIaF
+OG590

Fpg

22.0

-20:-90

606

1.0"

2

2

AAO

SERC-ER

ER

1984-98

IIIaF
+OG590

Fpg

22.0

-00:-15

288

1.0"

2

2

AAO/ROE

AAO-SR

GR

1996-99

IIIaF
+OG590

Fpg

22.0

S.Gal.plane

116

1.0"

2

2

AAO

SERC-I

IS

1990-02

IV-N
+RG715

Ipg

19.5

-00:-90

894

1.0"

2

2

AAO

SERC-QV

XV

1986-88

+GG495

Vpg

14.0

S.Gal.plane

94

1.0/1.7"

1+2

1

ROE

SERC-V
& PAL-V

XX

1979-85

IIIaJ
+GG495

Vpg

var.

M31, LMC,SMC

4

1.7"

1+2

1

STScI/ROE

## Search Tools

Search Guide Star Catalog
Search Digitized Sky Survey

## Image Gallery

### Sky Coverage - galactic

Sky coverage (in galactic coordinates) for the Guide Star Catalog, version 2.4.1.2

### Sky Coverage - equatorial

Sky coverage (in equatorial coordinates) for the Guide Star Catalog, version 2.4.1.2

### Optical Bands 1

Guide Star Catalog photometric bands, including GAIA G

### Optical Bands 2

Additional optical wavelength coverage in GSC2.

### Infrared Bands

Infrared coverage for the Guide Star Catalog