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.
The Astronomer's Knife for Astronomers
Ten sky tools — offline, portable, permanent
Your pocket observatory in a single file. The Astronomer's Knife gives astronomers 10 specialised tools in a single HTML file that runs entirely offline.
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
Why should Astronomers use The Astronomer's Knife?
The Astronomer's Knife is built for astronomers who need science & research tools without cloud dependencies. 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.
Does The Astronomer's Knife work offline?
Yes. The Astronomer's Knife is a single HTML file that runs entirely in your browser. No internet connection required. Your data never leaves your machine.
Is The Astronomer's Knife a subscription?
No. The Astronomer's Knife is a one-time purchase ($39). No monthly fees, no renewals, no price increases.
What tools are included in The Astronomer's Knife?
The Astronomer's Knife includes 10 tools: Tonight's Best, Sky Map, Celestial Events, Moon Phase Calculator, Solar Position Tracker, Sunrise & Sunset Calculator, Julian Date Converter, Constellation Guide (88), Magnitude & Distance Calculator, Planetary Position Finder. All accessible from a single HTML file.
Can I try The Astronomer's Knife before buying?
Yes. Every product page includes an interactive demo you can try in your browser. No signup required.
No cloud One fileOne-time purchase
Get The Astronomer's Knife — $39Sovereignty as a Service