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sdss.md

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1# SDSS SkyServer API

SDSS SkyServer API

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3## Base URL

5```

6https://skyserver.sdss.org/dr18/SkyServerWS

7```

9Replace `dr18` with the desired data release (e.g., `dr17`, `dr16`).

Base URL

https://skyserver.sdss.org/dr18/SkyServerWS

Replace dr18 with the desired data release (e.g., dr17, dr16).

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11## Authentication

13No API key required. All endpoints are public.

Authentication

No API key required. All endpoints are public.

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15## Key Endpoints

Key Endpoints

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17### 1. SQL Search (CasJobs-style free-form SQL)

19```

20GET /SearchTools/SqlSearch

21```

23| Parameter | Type | Description |

24|-----------|--------|-------------|

25| `cmd` | string | **Required.** SQL query against the selected SkyServer release schema; this synchronous API is separate from asynchronous CasJobs. |

26| `format` | string | `json`, `xml`, `csv`, `html`, `votable`. Default: `html`. |

28**Example — query 10 galaxies:**

29```

30https://skyserver.sdss.org/dr18/SkyServerWS/SearchTools/SqlSearch?cmd=SELECT TOP 10 objid,ra,dec,u,g,r,i,z FROM PhotoObj WHERE type=3&format=json

31```

33Type codes: `3` = galaxy, `6` = star.

35**Response (JSON, illustrative):**

36```json

37[

38 {"Rows": [

39 {"objid": 1237645941825863680, "ra": 195.123, "dec": 2.456, "u": 22.1, "g": 20.8, "r": 19.5, "i": 19.1, "z": 18.9}

40 ]}

41]

42```

44The response may contain a separate `SqlQuery` table alongside the result table. Select the result by `TableName` and validate its columns, rather than concatenating every `Rows` array.

1. SQL Search (CasJobs-style free-form SQL)

GET /SearchTools/SqlSearch

Parameter	Type	Description
`cmd`	string	Required. SQL query against the selected SkyServer release schema; this synchronous API is separate from asynchronous CasJobs.
`format`	string	`json`, `xml`, `csv`, `html`, `votable`. Default: `html`.

Example — query 10 galaxies:

https://skyserver.sdss.org/dr18/SkyServerWS/SearchTools/SqlSearch?cmd=SELECT TOP 10 objid,ra,dec,u,g,r,i,z FROM PhotoObj WHERE type=3&format=json

Type codes: 3 = galaxy, 6 = star.

Response (JSON, illustrative):

[
  {"Rows": [
    {"objid": 1237645941825863680, "ra": 195.123, "dec": 2.456, "u": 22.1, "g": 20.8, "r": 19.5, "i": 19.1, "z": 18.9}
  ]}
]

The response may contain a separate SqlQuery table alongside the result table. Select the result by TableName and validate its columns, rather than concatenating every Rows array.

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46### 2. Radial Search

48```

49GET /SearchTools/RadialSearch

50```

52| Parameter | Type | Description |

53|--------------|--------|-------------|

54| `ra` | float | **Required.** Right ascension (degrees). |

55| `dec` | float | **Required.** Declination (degrees). |

56| `radius` | float | Search radius in arcminutes. Default: 1. |

57| `format` | string | `json`, `xml`, `csv`. |

58| `limit` | int | Max results. |

59| `whichquery` | string | `imaging` or `spectro`, as supported by this search. |

60| `whichway` | string | Coordinate mode, e.g. `equatorial`. |

62**Example — objects within 2 arcmin of RA=180, Dec=+0.5:**

63```

64https://skyserver.sdss.org/dr18/SkyServerWS/SearchTools/RadialSearch?ra=180&dec=0.5&radius=2&whichway=equatorial&whichquery=imaging&format=json&limit=10

65```

2. Radial Search

GET /SearchTools/RadialSearch

Parameter	Type	Description
`ra`	float	Required. Right ascension (degrees).
`dec`	float	Required. Declination (degrees).
`radius`	float	Search radius in arcminutes. Default: 1.
`format`	string	`json`, `xml`, `csv`.
`limit`	int	Max results.
`whichquery`	string	`imaging` or `spectro`, as supported by this search.
`whichway`	string	Coordinate mode, e.g. `equatorial`.

Example — objects within 2 arcmin of RA=180, Dec=+0.5:

https://skyserver.sdss.org/dr18/SkyServerWS/SearchTools/RadialSearch?ra=180&dec=0.5&radius=2&whichway=equatorial&whichquery=imaging&format=json&limit=10

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67### 3. Rectangular Search

69```

70GET /SearchTools/RectangularSearch

71```

73| Parameter | Type | Description |

74|-----------|--------|-------------|

75| `min_ra` | float | Minimum RA (degrees). |

76| `max_ra` | float | Maximum RA (degrees). |

77| `min_dec` | float | Minimum Dec (degrees). |

78| `max_dec` | float | Maximum Dec (degrees). |

79| `format` | string | `json`, `xml`, `csv`. |

80| `limit` | int | Max results. |

3. Rectangular Search

GET /SearchTools/RectangularSearch

Parameter	Type	Description
`min_ra`	float	Minimum RA (degrees).
`max_ra`	float	Maximum RA (degrees).
`min_dec`	float	Minimum Dec (degrees).
`max_dec`	float	Maximum Dec (degrees).
`format`	string	`json`, `xml`, `csv`.
`limit`	int	Max results.

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82### 4. Object Lookup by ObjID

84```

85GET /SearchTools/SqlSearch?cmd=SELECT * FROM PhotoObj WHERE objid={objid}&format=json

86```

4. Object Lookup by ObjID

GET /SearchTools/SqlSearch?cmd=SELECT * FROM PhotoObj WHERE objid={objid}&format=json

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88### 5. Spectra Search by Plate-MJD-Fiber

90```

91GET /SearchTools/SqlSearch?cmd=SELECT * FROM SpecObj WHERE plate={plate} AND mjd={mjd} AND fiberid={fiberid}&format=json

92```

5. Spectra Search by Plate-MJD-Fiber

GET /SearchTools/SqlSearch?cmd=SELECT * FROM SpecObj WHERE plate={plate} AND mjd={mjd} AND fiberid={fiberid}&format=json

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94### 6. Image Cutout Service

96```

97GET /ImgCutout/getjpeg

98```

100| Parameter | Type | Description |

101|-----------|--------|-------------|

102| `ra` | float | **Required.** RA (degrees). |

103| `dec` | float | **Required.** Dec (degrees). |

104| `scale` | float | Arcsec/pixel. Default: 0.396127. |

105| `width` | int | Image width in pixels. Default: 512. |

106| `height` | int | Image height in pixels. Default: 512. |

107

108**Example:**

109```

110https://skyserver.sdss.org/dr18/SkyServerWS/ImgCutout/getjpeg?ra=180.0&dec=0.5&scale=0.4&width=256&height=256

111```

112

113Returns JPEG image data.

114

6. Image Cutout Service

GET /ImgCutout/getjpeg

Parameter	Type	Description
`ra`	float	Required. RA (degrees).
`dec`	float	Required. Dec (degrees).
`scale`	float	Arcsec/pixel. Default: 0.396127.
`width`	int	Image width in pixels. Default: 512.
`height`	int	Image height in pixels. Default: 512.

Example:

https://skyserver.sdss.org/dr18/SkyServerWS/ImgCutout/getjpeg?ra=180.0&dec=0.5&scale=0.4&width=256&height=256

Returns JPEG image data.

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115### 7. Spectrum Plot/Data

116

117Spectrum FITS files are on the [Science Archive Server](https://data.sdss.org/sas/dr18/). Paths depend on instrument, data release, reduction pipeline and plate/fiber formatting. Obtain the actual file URL from the selected release's object page or data model; do not construct one universal `spectro/sdss/redux` path for every survey.

118

7. Spectrum Plot/Data

Spectrum FITS files are on the Science Archive Server. Paths depend on instrument, data release, reduction pipeline and plate/fiber formatting. Obtain the actual file URL from the selected release's object page or data model; do not construct one universal spectro/sdss/redux path for every survey.

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119## Important SQL Tables

120

121| Table | Description |

122|-------------|-------------|

123| `PhotoObj` | Photometric measurements (positions, magnitudes). |

124| `SpecObj` | Spectroscopic measurements (redshifts, classifications). |

125| `Galaxy` | View of PhotoObj filtered to galaxies. |

126| `Star` | View of PhotoObj filtered to stars. |

127

128URL-encode `cmd` (for example `curl --get --data-urlencode "cmd=SELECT TOP 10 ..."`). Preserve 64-bit object IDs as integers or strings, not floating-point numbers.

129

Important SQL Tables

Table	Description
`PhotoObj`	Photometric measurements (positions, magnitudes).
`SpecObj`	Spectroscopic measurements (redshifts, classifications).
`Galaxy`	View of PhotoObj filtered to galaxies.
`Star`	View of PhotoObj filtered to stars.

URL-encode cmd (for example curl --get --data-urlencode "cmd=SELECT TOP 10 ..."). Preserve 64-bit object IDs as integers or strings, not floating-point numbers.

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130## Rate Limits

131

132No formal documented rate limits. Queries returning very large result sets may time out. Use `TOP N` in SQL queries to limit results. For bulk data, use CasJobs (https://skyserver.sdss.org/CasJobs/) with a free account.

Rate Limits

No formal documented rate limits. Queries returning very large result sets may time out. Use TOP N in SQL queries to limit results. For bulk data, use CasJobs (https://skyserver.sdss.org/CasJobs/) with a free account.

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