Comparison

zen vs Astrarium

Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.

Head to head
About

zen

Translate text and documents offline using your device. This app prioritizes privacy by keeping all data local, offering both fast machine translation and AI-powered options. It supports various file formats and image text extraction.

Highlights
  • Offline translation
  • On-device processing
  • Text and image translation
  • Supports various file types
  • Machine and AI translation options
  • Side-by-side comparison
Features
Read full description

zen-Babel is a translation app that works entirely offline. All translation is performed on your device—your data is never sent to the cloud. Simple to use: type, paste, or import text from files and images to translate. No ads. No subscriptions. A one-time purchase of 0.99 USD unlocks all features. With language packs from the standard Translate app, you can translate even without mobile data or Wi-Fi. zen-Babel supports text files, Word documents, PDFs, and text extraction from images. Even when connected to the internet, your documents never leave your device. This makes it ideal for translating sensitive business materials and privacy-critical content. Choose between fast, reliable machine translation and more natural AI-powered translation using Apple Intelligence. Use machine translation for speed, or AI translation for more fluent, context-aware results. The app also features Translation Clutch, which highlights the original text and translation side by side. You can quickly compare, understand, and refine translations—especially useful for long texts or fragmented conversations.

About

Astrarium

Explore the cosmos with an offline planetarium and sky atlas. View stars, nebulae, constellations, planets, and more with detailed information and adjustable time settings. Includes augmented reality features and export options.

Highlights
  • Offline sky charting
  • Detailed star and object catalogs
  • Adjustable time and location settings
  • Augmented reality view
  • Meteor shower calendar
  • Satellite tracking
  • PNG/PDF export
Features
Read full description

Choose a place and a time, and Astrarium draws that sky. Every position is computed on the device, so it works where there is no signal. The network is used only for comet and asteroid elements (MPC, JPL), satellite elements (CelesTrak), observed comet magnitudes (COBS) and the place picker's map tiles (OpenStreetMap) — each on your own action, each falling back to the cache. IN 11 LANGUAGES Japanese, English, Chinese (Traditional and Simplified), Korean, Spanish, Portuguese, French, German, Czech and Polish — the interface, and the names of constellations, stars, places and countries with it. CATALOGUES (all bundled) • 9,096 stars — Yale Bright Star Catalogue, to magnitude 8: all the naked eye can see • 155 nebulae, clusters and galaxies — Messier and Caldwell, with photographs • The 88 IAU constellations: 752 line segments from the official figures, and the classical art • The Milky Way, from NASA's Deep Star Maps 2020 — the light of 1.7 billion stars • Planets and the Moon from JPL DE421, with surface maps, libration and lunar age • 16 major meteor showers, MPC observatory codes, sites worldwide WHAT IT DOES • Whole-sky and horizon views, pinch zoom to an arcminute • Jump to any date, run the clock to 6000x, step by synodic month • Planet close-ups: apparent diameter, phase, distance, orbital elements, and the moons of Jupiter, Saturn and Mars • Meteor shower calendar: maximum in local time and UT, radiant altitude, moonlight, and an expected hourly rate from the ZHR • Comets and asteroids from the MPC and JPL • Satellites: the space stations and the naked-eye ones, with visible-pass predictions. Elements (TLEs) come from CelesTrak — refresh with “Download / update TLEs”, then it is all offline • Four coordinate grids, the ecliptic, equator, galactic plane and meridian, FOV frames for smart telescopes and lenses • Switch each layer on its own — lines, names, stars, Sun and planets, deep-sky objects, the Milky Way, the figures • Limiting magnitude that follows twilight and moonlight, red night-vision mode, PNG/PDF export, a captioned demo LOCATION Your position is used only to compute the sky where you are, and never leaves the device. Decline it and pick a site or type coordinates: nothing is lost. No ads, no account. All of the above is free, with no time limit. AR — the chart over the camera image — is free too. Sources and licences are listed under Credits. ASTRARIUM PRO (OPTIONAL SUBSCRIPTION) For observers who want to go deeper, an in-app subscription adds: • 3D solar system map — 1.56 million small bodies, comets and spacecraft, from above the ecliptic • Aurora forecast — NASA DONKI and NOAA OVATION, the oval on the sky and on a globe • Proper-motion time machine — 50,000 years either way; the figures come apart • Deep star catalogue — 2.34 million UCAC4 stars to 12th magnitude, below a 12-degree field • Exoplanet transits, variable-star maxima and minima • Every satellite group (Starlink, weather, science…), the world map and globe, search by name or ID • Equidistant (dome master) projection, local sidereal time US$3.99 a month or US$39.99 a year (US; prices vary by region). The first week is free; cancel any time. Payment is charged to your Apple ID at purchase and renews automatically unless cancelled at least 24 hours before the period ends. Manage or cancel in Settings > Apple ID > Subscriptions. Any unused part of a free trial is forfeited on purchase. Terms of Use (EULA): https://www.apple.com/legal/internet-services/itunes/dev/stdeula/ Privacy Policy: https://avellsky.github.io/Astrarium/privacy-policy.en.html APPLE WATCH Install it on iPhone and it goes to the watch too — free, like the rest. Tonight at a glance: when it gets dark and light again, the Moon's age and rise and set, which planets are up and where, the next satellite pass, any shower running. Plus a chart holding the whole sky in one disc, which the Digital Crown moves twelve hours either way.

Screenshots

zen4 screens
Astrarium4 screens

Verdict

The call

The clearest difference is review sentiment: zen at 100% against Astrarium's 50%. zen also leads on in-app purchases (none vs 2) and update cadence (every 5 days vs every 10 days). Astrarium's advantage is price (Free vs $0.99) and device support (4 vs 2). On ads there is nothing between them.

Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS

CostPrice · In-app purchases · Ads · Monetization

Astrarium is free to download; zen costs $0.99 up front. Astrarium sells 2 in-app purchases, starting at $3.99 per month. zen asks for nothing beyond the download.

UpkeepUpdate frequency

zen ships an update every 5 days, Astrarium every 10 days. Both last shipped on October 24, 2026.

Scorecard7 real differences · 1 level
zen versus Astrarium: the parameters behind the verdict, then further details
ParameterzenAstrarium
Price$0.99Free — better
Positive reviews100.0% of reviews — better50.0% of reviews
Update frequencyEvery 5 days — betterEvery 10 days
AdsNoNo
In-app purchasesNo — betterYes
MonetizationPaidFree — better
DevicesiPhone, iPadiPhone, iPad, Mac, Apple Watch — better
Requires iOS26.017.0 — better
Further details — not scored
Size6 MB132 MB
Age rating12+4+
DeveloperTaiyo FujiiShinsuke Abe

Customer experience

zen

Written reviews2 reviews
Positive100.0%
Neutral0.0%
Negative0.0%

Astrarium

Written reviews2 reviews
Positive50.0%
Neutral0.0%
Negative50.0%

In-app purchases

None

zen

No in-app purchases

2 purchases

Astrarium

Subscriptions2
  • Astrarium Pro Monthly7 Days trial$3.991 Month
  • Astrarium Pro Yearly7 Days trial$39.991 Year

Questions

Is zen free?
zen costs $0.99, with no in-app purchases.
Is Astrarium free?
Astrarium is free to download, with in-app purchases available.
Do zen or Astrarium have ads?
Neither zen nor Astrarium shows ads.
Which is updated more often, zen or Astrarium?
zen ships an update every 5 days, and Astrarium every 10 days. Most recently, zen was updated on October 24, 2026 and Astrarium on October 24, 2026.

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