About
Astrometry.net is a pioneering open-source astronomical image analysis platform that solves one of astronomy's most common challenges: determining exactly where in the sky an image was taken. Whether you have archival images with missing or unreliable coordinates, or freshly captured astrophotos from a backyard telescope, you can upload them to Astrometry.net's Nova web service and receive back fully calibrated astrometric metadata compliant with the FITS WCS standard. The service uses advanced pattern-matching algorithms that compare star positions in your image against comprehensive star catalogs to determine the precise pointing, orientation, and scale of your image — a process known as "plate solving." Once solved, it also returns lists of all known astronomical objects (stars, galaxies, nebulae, etc.) that fall within the field of view. Astrometry.net is built with the long-term goal of making every useful astronomical image ever taken — past and future — fully searchable, annotated, and scientifically usable. It is widely used by both amateur astronomers and professional researchers. The platform offers a web interface via Nova.astrometry.net, downloadable offline software for local use, and an API for programmatic integration into pipelines and observatories. Partially funded by NSF, NASA, and Canada's NSERC, the project is hosted by the Canadian Astronomy Data Center.
Key Features
- Automated Plate Solving: Identifies the exact sky coordinates, orientation, and scale of any astronomical image by matching star patterns against comprehensive star catalogs.
- WCS-Compliant Metadata Output: Returns astrometric calibration data in the FITS World Coordinate System (WCS) standard, making images immediately usable in professional astronomical software.
- Object Catalog Overlay: Provides a complete list of known astronomical objects — stars, galaxies, nebulae, and more — that fall within the calibrated field of view.
- Web Service & Downloadable Software: Available both as the Nova.astrometry.net hosted service and as downloadable open-source software for local or pipeline use.
- API Access: Programmatic API allows integration with automated telescope pipelines, observatories, and astronomical data-processing workflows.
Use Cases
- Amateur astronomers calibrating astrophotography images to add accurate sky coordinates before sharing or archiving.
- Professional researchers batch-processing archival astronomical plates or images that lack reliable coordinate metadata.
- Observatory pipelines automatically solving newly captured images in real time to enable downstream object identification and scheduling.
- Educators and students learning astrometry by uploading telescope images and examining the returned coordinate and object data.
- Developers building astronomy applications or tools that require automated plate-solving as a back-end service via the API.
Pros
- Completely Free: The service is free to use with no paywalls, funded by NSF, NASA, and NSERC — making it accessible to amateur and professional astronomers alike.
- Open Source: The underlying software is open source and can be downloaded for offline use, enabling local processing and custom integration into research pipelines.
- Works on Any Image: Can solve images from any telescope, camera, or archive regardless of missing or unreliable original metadata — even historical archival plates.
- Standards Compliant: Produces FITS WCS-standard output compatible with virtually all professional astronomical analysis tools and data archives.
Cons
- Limited to Astronomy Use Case: The tool is highly specialized for astronomical imaging and has no applicability outside of celestial coordinate calibration.
- Processing Time on Complex Images: Very wide-field, sparse, or low-quality images may take longer to solve or may fail if insufficient stars are detected.
- Minimal Modern UI: The Nova web interface is functional but dated, and lacks the polished user experience of modern web applications.
Frequently Asked Questions
What is plate solving and why do I need it?
Plate solving is the process of determining the precise celestial coordinates of an astronomical image by matching the star patterns in it against known star catalogs. You need it when your image lacks coordinate data, has incorrect pointing info, or when you need scientifically accurate WCS metadata for research or archiving.
What image formats does Astrometry.net accept?
The Nova.astrometry.net web service accepts common image formats including FITS, JPEG, PNG, and GIF, making it easy to submit images from any camera or telescope system.
Can I use Astrometry.net offline?
Yes. The core software is open source and can be downloaded and run locally. This is especially useful for automated telescope pipelines, observatories with limited internet connectivity, or batch processing of large image archives.
Is there an API for programmatic access?
Yes, Astrometry.net provides an API that allows developers and researchers to submit images and retrieve calibration results programmatically, enabling integration into automated observing pipelines and data processing workflows.
Who funds and maintains Astrometry.net?
The project is partially supported by the US National Science Foundation (NSF), NASA, and the Canadian National Science and Engineering Research Council (NSERC). The Nova web service is hosted by the Canadian Advanced Network For Astronomical Research (CANFAR) at the Canadian Astronomy Data Center.
