Beta 0.1.0 · for astrophysicists
The sky atlas that shows its work.
AstroTwo is a native macOS application to explore the sky, open FITS images, overlay catalogues and coverage maps, and ask an AI assistant to do it for you. Every number it shows comes from tested, deterministic code, and every action can be replayed.
ICRS 03h47m29.1s +24°06′18″
catalogue epoch J2016.0
source Gaia DR3 via CDS VizieR
catalog.load_region. It uses the network.
Why AstroTwo
An AI assistant you can check.
Most AI tools write numbers that sound right. In science that is not enough. AstroTwo is built so that the assistant can only act through AstroTwo's own commands, and so that you can always see where a value came from.
The AI never computes
Coordinates, distances and measurements come only from AstroTwo's scientific code. Each number in an answer is checked: verified numbers are underlined, invented ones are highlighted.
Every action is a command
Whatever you or the assistant do is recorded with its parameters, source and time. A saved session can be reopened and replayed exactly.
Protected against prompt injection
Text from catalogues and external services is treated as data, never as instructions. After reading external text, any action asks for your confirmation.
Your keys stay on your Mac
API keys live only in the macOS Keychain, never in files, logs or sessions. With a local model such as Ollama, nothing leaves your Mac.
Nothing is assumed
Epochs, reference frames, units and coordinate columns are read from the data, or asked to you. They are always declared next to the result.
Free and open source
AstroTwo is released under the GNU GPL v3 or later. You can read the code, verify the calculations and build it yourself.
Features
Everything you need to look at the sky.
Built on proven astronomy libraries such as Astropy, astroquery, PyVO and MOCPy, with a fast OpenGL sky viewer.
Sky viewer
- HiPS surveys such as DSS2 and 2MASS, colour and FITS tiles
- Smooth zoom and pan, Go to by name or coordinates
- ICRS and Galactic grids, north and east arrows, scale bar
- Pixel value under the cursor, with unit, HiPS order and resolution
Your images
- Open FITS images with their WCS
- Original pixel value and position under the cursor
- Image epoch read from the header, never assumed
- Background survey visible under the image, with opacity
Catalogues
- VizieR, SIMBAD and Gaia DR3, or your own CSV and VOTable files
- Proper motion propagated to the image epoch, with the epoch declared by the catalogue
- Table linked to the sky: select a row, see the source
- Colour-blind-safe symbols, distinct by shape in night mode
Coverage and layers
- MOC coverage maps
- Layers with visibility, order and opacity
- Layers of different bodies are never mixed by mistake
Tools
- Distance tool on the sky and on images
- SIMBAD pointer: hover or click to identify an object
- PNG export with data credits and provenance metadata
Interface
- Dark theme and red night mode for the observatory
- English and Italian
- Native macOS app: everything included, no Python to install
AI assistant
Ask. It acts. You verify.
The assistant is optional. AstroTwo works fully without it. When you use it, this is what happens.
You ask
"Go to the Pleiades and load Gaia DR3", in plain language.
It picks a command
The assistant can only use an explicit list of AstroTwo commands. Unknown or invalid requests are refused and explained.
You confirm
Commands that use the network or take long ask for your confirmation first.
Numbers are checked
AstroTwo compares every number in the answer with the results of the commands, and marks what it could not verify.
Bring your own provider
Use your own API key, or a local model for free and fully offline.
The assistant needs a model that supports tool calling. Paid providers charge your own account; with Ollama or LM Studio everything runs on your Mac.
Download
Install in a minute.
Download the .dmg
Python and every library are included. You do not need to install anything else.
Drag AstroTwo to Applications
Open the disk image and drag the app onto the Applications folder.
Allow the first launch
This beta is not yet signed by Apple, so macOS may block it. Open System Settings → Privacy & Security and click Open Anyway.
Requirements
- SystemmacOS 26 or later
- ProcessorApple Silicon (M1 or later)
- Memory8 GB is enough
- Sizeabout 250 MB
- Internetfor online surveys and catalogues
- AI assistantoptional, your own key or a local model
Intel Macs are not supported. The checksum (SHA-256) of each file is published on the GitHub release page.
Team plan
Working together, for free. Beta
For personal use you need nothing: no account, no sign-up. The Team plan is for groups, and it will always be free.
A team account
A team name and a password. If the name is already taken, you choose another one. No email and no personal data.
From any computer
Sign in to the team account from as many computers as you need.
Team assistant
A chatbot on this site to help organise your team. You choose the provider and use your own API key, which stays in your browser and is never stored on our server.
There is no password recovery. If you lose the password you can create a new team account, but everything in the old one is lost.
Licence and attributions
Open, and built on the work of others.
AstroTwo
Copyright © 2026 Guido Ratti. AstroTwo is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. It is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY. See the LICENSE and NOTICE files.
Third-party software
AstroTwo includes open-source libraries, each under its own licence, including Python (PSF), Astropy, astroquery, PyVO, MOCPy, astropy-healpix, reproject, NumPy, SciPy, Matplotlib, Pillow, keyring, SpiceyPy (with the NAIF/SPICE toolkit) and PySide6 with Qt (LGPL-3.0). Qt libraries are included unmodified and can be replaced. Icons in the app are from Lucide (ISC). The full list with every licence text is in THIRD_PARTY_LICENSES, also included inside the app.
Data and services
AstroTwo uses public data and services. If you use them in a publication, please follow the acknowledgement requested by each provider. The acknowledgement for each survey is shown in the app and written into exported images.
- CDS, Strasbourg Astronomical Observatory, France: SIMBAD, VizieR, Sesame, HiPS and MocServer.
- Digitized Sky Survey (DSS), Space Telescope Science Institute.
- Two Micron All Sky Survey (2MASS), University of Massachusetts and IPAC/California Institute of Technology, funded by NASA and the NSF.
- Gaia, European Space Agency (ESA), data processed by the Gaia Data Processing and Analysis Consortium (DPAC).
- NAIF/SPICE, NASA Jet Propulsion Laboratory.
This website
All illustrations on this page are drawn in code for this site; no third-party images are used. The site uses no tracking. The only cookie is a session cookie, set only when you sign in to a Team account. Team accounts store only the team name, a salted hash of the password (never the password itself) and session data. The counters store only two numbers: page visits and download clicks. They count page loads, not individual people.
Independence
AstroTwo is an independent project. It is not affiliated with or endorsed by CDS, the Aladin team, ESA, NASA, STScI, Apple or any AI provider. All names and trademarks belong to their owners.