To download a public survey image, use an official archive: ESO’s Online Digitized Sky Surveys service for DSS images, or MAST’s Image Cutout Service for Pan-STARRS1 (PS1). Enter an object name or supported J2000 coordinates, choose a survey band and field size, then select an image format. Use JPEG or GIF for quick viewing; choose FITS when you need an astronomy image file with metadata. A downloadable image is not automatically a calibrated, linear science product, so check the archive’s documentation before analyzing pixel values.
Choose a service for the survey you need
Start by deciding whether you want a Digitized Sky Survey (DSS) image or a Pan-STARRS1 (PS1) image. The archives provide different survey data and access routes; they are not interchangeable versions of one image. Your choice should match both the sky survey you want and the kind of file or area you need.
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| Service | Survey and access | Formats and image size | Best fit |
|---|---|---|---|
| ESO Online Digitized Sky Surveys | DSS, with a browser form and a documented remote client for repeat or batch retrievals. The service also implements the International Virtual Observatory Alliance’s Simple Image Access Protocol (SIAP). | The form lets you choose image dimensions, survey, and output format. The remote client retrieves FITS images. The ESO form’s current format options are shown by the live service. | A one-off DSS image through the form, or scripted/multiple DSS requests through the client. |
| STScI MAST DSS | DSS image extractions through the MAST service. | FITS, JPG, or GIF extractions. | Obtaining a DSS extraction in one of the stated formats. |
| MAST PS1 Image Cutout Service | Pan-STARRS1 images, with interactive browsing and a notebook example for scripted downloads. | Color views, JPEG and FITS cutouts, and retrieval of larger skycell images. | Viewing or downloading a PS1 cutout, or retrieving a larger skycell image. |
For a handful of images, a browser interface is usually the straightforward route. If you need repeated DSS retrievals or want to incorporate them into a script, ESO documents a command-line client. MAST’s PS1 notebook example is the documented starting point for scripted PS1 downloads.
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These access routes solve related but distinct problems. ESO’s browser form is oriented toward configuring an individual DSS extraction; the remote client is useful when requests need to be repeated or automated. MAST’s PS1 service combines interactive exploration and cutout downloads with a route to larger skycell images. MAST’s DSS service is another option specifically for DSS extractions. Compare the survey, area, format, and number of requests before choosing rather than assuming one archive has the same controls as another.
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Find the target by name or coordinates
ESO’s online DSS form accepts an astronomical object name or J2000 right ascension and declination. Its remote client can also resolve an object name through SIMBAD. The exact name and coordinate controls vary among MAST interfaces; follow the instructions shown by the relevant service.
If you have an object name
- Open the ESO Online Digitized Sky Surveys form or a MAST service appropriate to the survey.
- Enter the object name in the service’s target field. For the ESO remote-client workflow, name resolution through SIMBAD is optional.
- Check the returned target or image before downloading. If you are automating ESO requests, follow the client documentation for the name-resolution option rather than assuming the client resolves names by default.
An object name is convenient when the archive recognizes the target and you want an image centered on that named object. Names may be less suitable when you are targeting a particular point near an object, working with an unnamed field, or preparing a repeatable automated request. In those cases, coordinates let you specify the location directly. In either workflow, take a moment to check the position shown or returned before saving the file; a correctly downloaded image can still be the wrong field if the target was entered incorrectly.
If you have coordinates
- Use J2000 right ascension (RA) and declination (Dec) in the ESO online form or remote client.
- Enter the coordinate values in the fields requested by the service, and confirm that the location shown or returned is the intended sky position.
- Specify the field of view when using the ESO remote client. Its documentation gives a 10 by 10 arcminute field as an example, not as a required or universal size.
Names are convenient for familiar objects; coordinates are useful when the target is a specific position rather than a named object. Coordinates also make it easier to request the same position again or construct a series of related requests. Use the coordinate convention requested by the archive: ESO specifically identifies J2000 RA and Dec for its DSS form. Do not silently substitute another coordinate convention or infer input formatting from a different service.
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Choose a DSS survey band with its coverage in mind
DSS2 has blue, red, and infrared survey options, but their reported sky coverage differs. The ESO service page, accessed in 2026, reports these figures:
| DSS2 survey | Reported sky coverage |
|---|---|
| DSS2-blue | 45% |
| DSS2-red | 98% |
| DSS2-infrared | 99% |
These are the coverage figures stated on the ESO page, not a guarantee that every requested field is available in every band. If a location does not return the image you expect, try a band whose reported coverage is broader or consult the service’s current coverage information. Do not assume that the bands have identical coverage. The difference is substantial: the blue survey’s reported coverage is less than half the sky, while the red and infrared figures are close to all-sky coverage. That makes checking the selected band a practical troubleshooting step, not just a technical detail.
Coverage is only one part of band selection. If you have a specific reason to inspect a blue, red, or infrared view, select that survey and check whether it covers the position. If you mainly need an available DSS image of a target and one band has no result, another band may provide a useful visual reference. A different band, however, is a different view of the survey data; it should not be treated as an identical substitute.
For PS1, the documented broadband filters are g, r, i, z, and y. MAST’s cutout service supports interactive browsing and color views as well as JPEG and FITS cutouts. Choose a band or view according to what you want to inspect; the listed filter names alone do not establish that one view is best for every target or analysis. Filter selection and file format are separate decisions: the filter describes the PS1 view, while JPEG or FITS describes the downloaded representation.
Set the field size and retrieve the image
One-off DSS image from ESO’s browser form
- Open the ESO Online Digitized Sky Surveys service.
- Provide an object name or J2000 RA and Dec.
- Select the survey, image dimensions, and output format in the form.
- Submit the request and inspect the returned image or file. If the field is not useful, adjust the dimensions and request another extraction.
The form is appropriate for individual lookups because it exposes the target, dimensions, survey, and format choices together. Think about how much surrounding sky is useful: a field tightly focused on a target is easier to inspect, while a broader field can show more context. No single field size is prescribed for every purpose. Exact current control labels and available format options can change; use the choices displayed by the live service.
Repeated or automated DSS retrievals
ESO documents a remote DSS client for multiple requests in one command and for integration with scripts or automated observing tools. The client takes coordinates and a requested field of view, can optionally resolve an object name through SIMBAD, and retrieves FITS images. The documented 10 by 10 arcminute example is a sample request size.
- Check ESO’s current remote-client instructions and supported download before installing. The documentation identifies version 2.5x and Linux x86 support, and says several older platforms are no longer supported; these are version/platform details to verify against current instructions, not a promise of compatibility on a particular machine.
- Prepare the target coordinates and the desired field of view, or configure the optional SIMBAD name resolution described in the client documentation.
- Submit one request first and confirm that the returned FITS image covers the intended location and field.
- Once the request is correct, use the client’s documented method for multiple requests or integrate it into your script. Copy command syntax from ESO’s current client documentation rather than relying on an assumed command.
Testing one request before running a batch helps catch errors in the target, field of view, or setup before they are repeated across many retrievals. It also lets you confirm that the client is returning the FITS product you expect. For recurring work, keep the chosen parameters consistent across requests and retain the associated files and metadata; if you change the band or field size, record that change so the resulting images are not mistaken for identical extractions.
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- Open MAST’s PS1 Image Cutout Service.
- Use its interactive browsing tools to find the desired position and inspect the available color view or filter options.
- Choose a JPEG or FITS cutout for a smaller view, or use the service’s retrieval option for larger skycell images when a cutout is not enough.
- For a scripted workflow, follow MAST’s notebook example and the current service documentation.
A cutout is useful when you need a particular field around a target. The option to retrieve larger skycell images serves a different need: access to a larger image unit rather than only a small displayed region. Start with the smaller cutout if it provides the area you need; choose the larger-image route when your task requires more sky coverage than the cutout offers. The MAST service documents both options, so the choice is about area and workflow rather than assuming that a larger file is always preferable.
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Choose a format for viewing or analysis
| Format | Useful for | What to keep in mind |
|---|---|---|
| JPEG | Quick visual inspection; MAST offers PS1 JPEG cutouts. | A display-friendly image is not by itself evidence of calibrated, linear pixel data. |
| GIF | Quick visual inspection; MAST DSS extractions are offered in GIF. | Use an astronomy-oriented file and its documentation if you need image metadata or analysis. |
| FITS | Astronomy viewing and analysis workflows. ESO says its DSS extractions include header keywords that relate pixel positions to celestial coordinates. | FITS is a suitable data format, but the format alone does not establish calibration or the scientific meaning of pixel values. |
ESO notes that DSS FITS extractions can be viewed, converted, or analyzed with astronomy packages. The header information matters because it connects image pixels to positions on the sky. If you need to work with coordinates or perform analysis, preserve the FITS file and its header rather than treating a rendered JPEG or GIF as an equivalent data file.
For a quick visual check, the simplest available display format may be enough. A JPEG or GIF is convenient to open and share for visual inspection, but it should not be confused with an astronomy data product just because it depicts the same sky area. If you need to retain coordinate-related header information or use the image in an astronomy workflow, select FITS where available. These are practical format choices, not claims that one format guarantees a particular scientific quality.
Also distinguish an image view from its source survey and filter. A color view can be useful for browsing, while a specific filter image may better suit a particular inspection task. The available format does not itself tell you which survey band was used or whether the pixel values are suitable for measurement; check the product details in the archive.
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File format and scientific suitability are separate questions. A FITS file can carry useful astronomy metadata, but that does not mean every image is a calibrated, linear science product. MAST specifically warns that pixel values in PS1 stack images are related non-linearly to flux. Do not interpret those values as directly proportional to flux without checking MAST’s documentation for the particular image product and intended use.
- For a visual reference, use the display image or color view that serves the task.
- For image coordinates or analysis, prefer the FITS product and retain its header metadata.
- For quantitative work, consult the relevant archive documentation before interpreting pixel values, calibration, or flux.
This distinction prevents a common mistake: assuming that downloading an image in an astronomy file format makes its pixel values immediately suitable for scientific measurement. FITS tells you the kind of file you have, not by itself how the image was processed or how its values relate to physical quantities. In particular, the warning about PS1 stack values applies when interpreting those values as flux; it is a reason to consult the product documentation, not a reason to avoid using PS1 images for visual browsing.
If you only need to recognize a field or make a visual comparison, a rendered image may meet the need. If you intend to measure brightness or draw a quantitative conclusion, first identify the exact product and read the archive’s instructions about its values. Keep the distinction clear in any downstream work: a visually useful image and a quantitatively interpretable dataset are not automatically the same thing.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Troubleshoot a result that is missing or unsuitable
The target does not appear where expected
- Check the entered name or J2000 RA and Dec and verify the returned position.
- If using ESO’s batch client, confirm that optional SIMBAD name resolution is configured as intended.
- For DSS2, check the selected band’s coverage. ESO’s stated figures vary from 45% for blue to 98% for red and 99% for infrared.
Do not assume that changing the output format will fix a missing field: format controls how an available image is delivered, not which part of the sky was requested. First check the target, then the band and coverage. If the archive returns an image but it does not look like the expected area, verify the position before requesting the same coordinates in another format.
The image is too small or too large
- For ESO DSS, change the image dimensions in the browser form or the field of view in the remote-client request.
- For PS1, select a cutout for a focused region or retrieve a larger skycell image if you need more area.
- Do not treat ESO’s 10 by 10 arcminute client example as a default requirement.
Choose the field size based on the context you want to see, then inspect the result. A compact cutout can be convenient for a single target; more area may help when the surrounding field matters. The documented client example shows that a 10 by 10 arcminute request is possible, but ESO does not present it as a universal recommendation.
The download is inconvenient to view or analyze
- Choose JPEG or GIF when the goal is simply visual inspection and the service offers that format.
- Choose FITS when you need astronomy metadata and an astronomy analysis workflow.
- For PS1 stack measurements, consult MAST’s product documentation because the stated pixel-value relationship to flux is non-linear.
When comparing two downloads, confirm that they refer to the same target, field, survey, and view before attributing a difference to the file format. For analysis, retain the FITS header and consult the archive’s product-specific guidance. For display, choose a convenient format without assuming it preserves the same metadata or numerical interpretation as FITS.
The ESO client does not install or run
Check the current ESO download instructions for version and platform support. The documentation identifies a version 2.5x client and Linux x86 support, while noting that several older platforms are no longer supported. These details may change, so check the live instructions rather than treating them as a guarantee of present-day compatibility. If the client is unsuitable for your platform or task, the ESO browser form is also documented for individual requests.
Quick decision guide
- Need one DSS image: use ESO’s browser form or the MAST DSS service; choose a band, field dimensions, and format.
- Need several DSS images or scripted retrieval: use ESO’s documented remote client and test a single request before automating multiple requests.
- Need a PS1 image: use MAST’s Image Cutout Service; select a cutout or retrieve a larger skycell image as appropriate.
- Need an image just to look at: choose a JPEG or GIF option where available.
- Need astronomy metadata or intend to analyze the image: use FITS and check the archive’s product-specific guidance before interpreting pixel values.
A practical sequence is to choose the survey first, then identify the target, set the field size, and select the output format. Next, inspect the returned image and confirm its location and extent. If you need repeated access, move to the documented batch or notebook workflow only after a one-off request works. Finally, decide whether you need a view for inspection or data for analysis; the file extension alone cannot settle the latter question.
Archive interfaces, formats, platform support, and coverage descriptions can change. Confirm the current instructions in the relevant ESO or MAST service before building a workflow around a particular option.
Frequently Asked Questions
How do I download a sky image for specific coordinates?
For ESO DSS, enter J2000 right ascension and declination in the online form, then select the survey, image dimensions, and format. For repeat requests, ESO documents a remote client that takes coordinates and a requested field of view. Check the returned position and image extent before using the file.
Where can I get a FITS image of an object?
ESO’s DSS remote client retrieves FITS images, and MAST offers DSS extractions in FITS. MAST’s PS1 Image Cutout Service also offers FITS cutouts and larger skycell image retrieval. Choose the archive based on whether you need DSS or PS1.
How do I download a Pan-STARRS image cutout?
Use MAST’s PS1 Image Cutout Service. It supports interactive browsing, color views, and JPEG or FITS cutouts. It also offers larger skycell image retrieval when a cutout does not provide enough area; MAST’s notebook example is its documented starting point for scripted downloads.
Should I choose JPEG, GIF, or FITS?
JPEG or GIF is convenient for quick visual inspection where offered. FITS is suited to astronomy workflows and can preserve useful metadata; ESO says its DSS FITS extractions include header keywords relating pixel positions to celestial coordinates. FITS does not by itself guarantee that the image is calibrated or that its values are suitable for measurement.
Why might a DSS image be unavailable in one band?
DSS2 band coverage differs. ESO’s service page, accessed in 2026, reports 45% sky coverage for DSS2-blue, 98% for DSS2-red, and 99% for DSS2-infrared. Check the chosen band and current service coverage; a different band may cover a location that is not available in the first one.
Can I use PS1 stack pixel values as direct measurements of flux?
Do not assume so. MAST warns that pixel values in PS1 stack images are related non-linearly to flux. Consult MAST’s documentation for the specific product and intended use before interpreting those values quantitatively.
Can I use ESO’s 10 by 10 arcminute request for every image?
No. ESO gives 10 by 10 arcminutes as an example field size for its remote client, not a universal default or requirement. Specify the field of view that fits your task and verify the returned extent.
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The Bottom Line
Use ESO for DSS and MAST for PS1, choosing the access route and field size for a one-off image or a repeat workflow. Pick JPEG or GIF for a convenient visual view and FITS when you need astronomy metadata, but check the archive’s product guidance before treating any downloaded pixels as quantitative measurements.
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