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.
Observe the Sky with The Astronomer's Knife
Ten sky tools — offline, portable, permanent
You need to observe the sky. Your pocket observatory in a single file. The Astronomer's Knife delivers 10 purpose-built tools in a single HTML file.
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 help me observe the sky?
The Astronomer's Knife provides 10 interconnected tools for your pocket observatory in a single file. 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.
Do I need an internet connection to observe the sky with The Astronomer's Knife?
No. The Astronomer's Knife runs entirely in your browser as a single HTML file. All 10 tools work offline.
What is the difference between The Astronomer's Knife and cloud-based alternatives?
Cloud tools store your data on external servers, require subscriptions, and stop working without internet. The Astronomer's Knife is a one-time purchase ($39) that runs locally. Your data never leaves your device.
Can I use The Astronomer's Knife on multiple devices?
Yes. Once purchased, you can use The Astronomer's Knife on any device with a web browser. Copy the HTML file to as many devices as you need.
No cloud One fileOne-time purchase
Get The Astronomer's Knife — $39Sovereignty as a Service