About
ASTAP, the Astrometric STAcking Program, is a comprehensive and free astronomical imaging tool designed for astrophotographers and researchers who need reliable plate solving, image stacking, and photometry capabilities. It serves as a capable replacement for PlateSolve2 and astrometry.net, offering a self-contained solution that works offline with downloadable star databases. At its core, ASTAP solves astrometric (plate) fields by matching star patterns in captured images against extensive star catalogs, including databases ranging from D05 to D80 with density limits up to 8,000 stars per square degree, going as deep as magnitude 21. This makes it effective even in star-poor regions of the sky. For image processing, ASTAP supports full stacking with reverse mapping and bilinear interpolation, delivering reduced background noise and improved star shapes. It also includes an image stitching and mosaic routine for combining wide-field panels. The built-in FITS viewer allows direct inspection of astronomical image files. Photometry features include dedicated star databases (V50, V05) containing Johnson-V magnitudes and Gaia Bp-Rp data, enabling accurate stellar brightness measurements. Optional databases cover 5 million galaxies (HyperLeda) and variable star positions. ASTAP is available for Windows (32/64-bit), Linux (Debian, Arch, openSUSE, Fedora), macOS (Intel and Apple Silicon), and Raspberry Pi (32/64-bit), making it one of the most cross-platform free tools in amateur astronomy.
Key Features
- Astrometric Plate Solving: Accurately identifies the sky coordinates of any captured image by matching star patterns against large downloadable star databases (D05–D80), working in star-poor and star-rich fields alike.
- Image Stacking: Combines multiple exposures using reverse mapping with bilinear interpolation to reduce background noise and improve star shape in the final stacked image.
- Photometry Analysis: Measures stellar brightness using dedicated V50/V05 photometry databases containing Johnson-V magnitudes and Gaia Bp-Rp data for accurate stellar photometry.
- FITS Viewer: Built-in viewer for inspecting FITS (Flexible Image Transport System) files, the standard format used in professional and amateur astronomy.
- Image Stitching & Mosaics: Automatically combines multiple overlapping panels into wide-field mosaic images, with a significantly optimized stitching routine for faster processing.
Use Cases
- Astrophotographers using plate solving to precisely align and calibrate telescope pointing for imaging sessions
- Amateur astronomers stacking multiple long-exposure images to reduce noise and reveal faint deep-sky objects
- Researchers and students performing stellar photometry to measure variable star brightness over time
- Astronomy clubs and observatories building wide-field mosaic images by stitching together multiple panels
- Telescope automation setups using ASTAP as an offline plate solver integrated with imaging software
Pros
- Completely Free: ASTAP is available at no cost for all supported platforms, making professional-grade astrometric tools accessible to hobbyists and researchers alike.
- Cross-Platform Support: Runs on Windows (32/64-bit), Linux (multiple distros), macOS (Intel and Apple Silicon), and Raspberry Pi, covering virtually every desktop environment.
- Flexible Star Databases: Offers multiple star database sizes and types (D05–D80, photometry, galaxy, variable star) so users can balance storage and depth based on their telescope setup.
- Works Offline: Once star databases are downloaded, plate solving and stacking work entirely offline without needing an internet connection.
Cons
- Learning Curve for Beginners: The variety of database options, platform-specific instructions, and technical astronomy concepts can be overwhelming for newcomers to astrophotography.
- Linux UI Limitations: The GTK3-based Linux versions still have layout issues with buttons and input fields, making the interface less polished than the Windows or macOS versions.
- Large Storage Requirements: The largest star database (D80) requires approximately 1.25 GB of storage, and optional galaxy/variable star databases add further disk space requirements.
Frequently Asked Questions
What is ASTAP used for?
ASTAP is used for astrometric plate solving (identifying the sky coordinates of an image), stacking multiple astronomical exposures to improve image quality, performing photometry measurements, and viewing FITS image files.
Which star database should I download?
If your telescope's field of view is 0.6 degrees or larger, any database from D05 to D80 will work. D05 is the smallest (~smallest storage), while D80 is the largest (~1.25 GB) but offers no functional drawback other than file size. For photometry, download the V50 or V05 database.
Is ASTAP free to use?
Yes, ASTAP is completely free to download and use for all platforms including Windows, Linux, macOS, and Raspberry Pi.
Can ASTAP replace PlateSolve2 or astrometry.net?
Yes, ASTAP is widely used as a replacement for both PlateSolve2 and astrometry.net. It works offline once star databases are installed and is considered highly reliable across a wide range of telescope setups.
Does ASTAP work on Apple Silicon Macs?
Yes, ASTAP has a dedicated build for Apple Silicon (M-series) Macs that is significantly faster than the Intel version, though it requires code signing and does not include Dcraw or FITS compression support.
