144 lines
4.0 KiB
Markdown
144 lines
4.0 KiB
Markdown
---
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title: "SDSS SkyServer API"
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task: ""
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lineage_type: import
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upstream_source: https://github.com/K-Dense-AI/scientific-agent-skills/blob/9c9bd2e9/skills/database-lookup/references/sdss.md
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upstream_sha: 9c9bd2e9
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imported_at: 2026-06-26
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prompt_class: prompt
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upstream_changes: accepted
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author: upstream
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validated: false
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---
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# SDSS SkyServer API
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## Base URL
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```
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https://skyserver.sdss.org/dr18/SkyServerWS
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```
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Replace `dr18` with the desired data release (e.g., `dr17`, `dr16`).
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## Authentication
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No API key required. All endpoints are public.
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## Key Endpoints
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### 1. SQL Search (CasJobs-style free-form SQL)
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```
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GET /SearchTools/SqlSearch
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```
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| Parameter | Type | Description |
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|-----------|--------|-------------|
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| `cmd` | string | **Required.** SQL query against SDSS CasJobs schema. |
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| `format` | string | `json`, `xml`, `csv`, `html`, `votable`. Default: `html`. |
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**Example — query 10 galaxies:**
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```
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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
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```
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Type codes: `3` = galaxy, `6` = star.
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**Response (JSON):**
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```json
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[
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{"Rows": [
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{"objid": 1237645941825863680, "ra": 195.123, "dec": 2.456, "u": 22.1, "g": 20.8, "r": 19.5, "i": 19.1, "z": 18.9}
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]}
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]
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```
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### 2. Radial Search
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```
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GET /SearchTools/RadialSearch
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```
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| Parameter | Type | Description |
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|--------------|--------|-------------|
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| `ra` | float | **Required.** Right ascension (degrees). |
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| `dec` | float | **Required.** Declination (degrees). |
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| `radius` | float | Search radius in arcminutes. Default: 1. |
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| `format` | string | `json`, `xml`, `csv`. |
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| `limit` | int | Max results. |
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| `objtype` | string | Filter: `star`, `galaxy`, or blank for all. |
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**Example — objects within 2 arcmin of RA=180, Dec=+0.5:**
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```
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https://skyserver.sdss.org/dr18/SkyServerWS/SearchTools/RadialSearch?ra=180&dec=0.5&radius=2&format=json&limit=10
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```
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### 3. Rectangular Search
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```
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GET /SearchTools/RectangularSearch
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```
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| Parameter | Type | Description |
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|-----------|--------|-------------|
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| `min_ra` | float | Minimum RA (degrees). |
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| `max_ra` | float | Maximum RA (degrees). |
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| `min_dec` | float | Minimum Dec (degrees). |
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| `max_dec` | float | Maximum Dec (degrees). |
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| `format` | string | `json`, `xml`, `csv`. |
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| `limit` | int | Max results. |
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### 4. Object Lookup by ObjID
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```
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GET /SearchTools/SqlSearch?cmd=SELECT * FROM PhotoObj WHERE objid={objid}&format=json
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```
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### 5. Spectra Search by Plate-MJD-Fiber
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```
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GET /SearchTools/SqlSearch?cmd=SELECT * FROM SpecObj WHERE plate={plate} AND mjd={mjd} AND fiberid={fiberid}&format=json
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```
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### 6. Image Cutout Service
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```
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GET /ImgCutout/getjpeg
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```
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| Parameter | Type | Description |
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|-----------|--------|-------------|
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| `ra` | float | **Required.** RA (degrees). |
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| `dec` | float | **Required.** Dec (degrees). |
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| `scale` | float | Arcsec/pixel. Default: 0.396127. |
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| `width` | int | Image width in pixels. Default: 512. |
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| `height` | int | Image height in pixels. Default: 512. |
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**Example:**
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```
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https://skyserver.sdss.org/dr18/SkyServerWS/ImgCutout/getjpeg?ra=180.0&dec=0.5&scale=0.4&width=256&height=256
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```
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Returns JPEG image data.
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### 7. Spectrum Plot/Data
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Spectrum FITS files can be retrieved from the Science Archive Server:
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```
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https://data.sdss.org/sas/dr18/spectro/sdss/redux/{run2d}/spectra/{plate}/spec-{plate}-{mjd}-{fiberid}.fits
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```
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## Important SQL Tables
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| Table | Description |
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|-------------|-------------|
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| `PhotoObj` | Photometric measurements (positions, magnitudes). |
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| `SpecObj` | Spectroscopic measurements (redshifts, classifications). |
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| `Galaxy` | View of PhotoObj filtered to galaxies. |
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| `Star` | View of PhotoObj filtered to stars. |
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## Rate Limits
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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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