Tonight's Best
Analyses your location, date, moon phase, and sky darkness to recommend the best deep-sky objects, planets, and events visible tonight — ranked by observability.
Your tools stop working when the Wi-Fi does
The Astronomer's Knife is the answer
Field work. Remote locations. Unreliable connections. Air-gapped environments. Cloud tools become expensive paperweights. Every tool works offline, forever. Open the HTML file, do your work. No login, no sync, no server required.
The Astronomer's Knife is a single-file knife with 10 tools that runs entirely in your browser. The Astronomer's Knife puts ten essential astronomy tools into a single HTML file that works offline, forever. Tonight's Best analyses your location, date, moon phase, and weather to recommend the best objects to observe right now. The interactive Sky Map renders your local sky in real time. A Celestial Events calendar tracks eclipses, meteor showers, conjunctions, and oppositions. Calculate moon phases with visual displays, track the sun's position and arc, compute sunrise and sunset times for any location, convert between Julian and calendar dates, browse 88 constellations with detailed guides, calculate stellar magnitudes and distances, and find planetary positions with visibility data — all without an internet connection. Your observations stay on your machine.
WHAT'S INSIDE
10 tools in a single HTML file
Sky Map
Interactive overhead sky chart for your location and time. Shows constellations, planets, and cardinal directions. Drag to change time, pinch to zoom.
Celestial Events
Calendar of upcoming eclipses, meteor showers, conjunctions, oppositions, and transits. Filter by type and get visibility predictions for your latitude.
Moon Phase Calculator
Calculate the moon's phase for any date with a visual display showing illumination percentage, phase name, and age in days.
HOW IT WORKS
Three steps. No setup.
1
Download the file
Purchase The Astronomer's Knife and download a single HTML file. No installer, no account, no setup.
2
Open in any browser
Double-click to open in Chrome, Firefox, Safari, or Edge. Works on any operating system.
3
Start working
Your data stays in your browser's local storage. Nothing is uploaded. Ever.
COMPLIANCE & GEOGRAPHY
Global
Works in any country. No server dependency, no regional restrictions.
FAQ
Frequently Asked Questions
How does The Astronomer's Knife solve the working without internet problem?
The Astronomer's Knife runs entirely in your browser. Field work. Remote locations. Unreliable connections. Air-gapped environments. Cloud tools become expensive paperweights. Every tool works offline, forever. Open the HTML file, do your work. No login, no sync, no server required. Tonight's Best advisor, interactive sky map, celestial events calendar, moon phase calculator, solar position tracker, sunrise/sunset times, Julian date converter, constellation guide, magnitude calculator, and planetary positions. Your pocket observatory in a single file.
Is my data safe with The Astronomer's Knife?
Yes. The Astronomer's Knife is a single HTML file. It never connects to any server. Your data stays in your browser's local storage on your device.
What makes The Astronomer's Knife different from cloud tools?
Cloud tools require internet, charge subscriptions, and store your data externally. The Astronomer's Knife is a one-time purchase ($39), works offline, and never transmits data.
Is The Astronomer's Knife really just one file?
Yes. The Astronomer's Knife is a single HTML file containing 10 tools. Download it, open it in any browser, and start working. No installation, no dependencies, no accounts.
No cloud One fileOne-time purchase
Get The Astronomer's Knife — $39Sovereignty as a Service