Offline Astronomy App for Planets, Moon Phases, Satellites, and Sky Tracking

Why offline matters for astronomy

The best stargazing conditions are usually the worst connectivity conditions. Dark-sky sites, remote campsites, open desert, high altitude, offshore boats, and rural fields tend to have weak or unavailable mobile data. An astronomy app that depends on a cloud connection becomes unreliable exactly when you need it most.

SIMT solves this by running all sky calculations on device. Planetary positions use VSOP87 theory, satellite orbits use SGP4 propagation from TLE data, and Moon phase and position logic follows standard astronomical algorithms. None of these require a network call at the moment of use.

Tracking planets and the solar system

SIMT can show you where each visible planet is in the sky at any given time. The positions are calculated using VSOP87 theory, the same mathematical model used by professional ephemeris services, adapted for on-device computation. You can check the current altitude and azimuth of Mercury, Venus, Mars, Jupiter, Saturn, and more without opening a browser or waiting for a data fetch.

The live Orrery view takes this further by rendering a real-time scale model of the solar system. You can see where the planets are in their orbits relative to the Sun and Earth, which helps build an intuitive sense of why certain planets are visible at certain times of year.

• Planetary positions calculated with VSOP87 theory, entirely on device.
• Live Orrery view shows current orbital positions of all major planets.
• Altitude and azimuth data helps you locate planets in the actual sky.
• No internet required for any planetary calculation or display.

Moon phases and lunar position

Knowing the current Moon phase and position matters for more than casual curiosity. Photographers plan around golden hour and moonrise timing. Hikers and campers gauge how much natural light they will have after dark. Astronomers check whether the Moon will wash out faint deep-sky targets. Anglers and hunters sometimes factor lunar phase into activity planning.

SIMT computes Moon phase, illumination percentage, rise and set times, and current sky position using standard lunar algorithms. The data updates continuously and does not depend on a server lookup, so it works at a remote campsite just as well as at home.

• Current Moon phase with illumination percentage displayed in real time.
• Moonrise and moonset times calculated for your current location.
• Lunar sky position shown alongside planetary and satellite data.
• Useful for photography planning, stargazing sessions, and outdoor activities.

Satellite tracking with TLE data

SIMT tracks satellites using Two-Line Element (TLE) data and the SGP4 propagation model. TLE sets describe the orbital parameters of a satellite at a specific epoch, and SGP4 projects those parameters forward in time to predict where the satellite will be at any given moment.

You can update TLE data when you have connectivity and then use the predictions offline for days or weeks afterward. This makes satellite tracking practical in the field, during travel, or at remote observing sites where downloading fresh data is not an option.

• SGP4 propagation model for accurate satellite position prediction.
• TLE data can be refreshed when connected and used offline afterward.
• Track the ISS, Starlink trains, weather satellites, and other objects.
• Pass predictions include timing, direction, and elevation above the horizon.

Celestial targets and deep-sky objects

Beyond planets and satellites, SIMT supports celestial targets that let you save and track positions of deep-sky objects, bright stars, or any custom sky coordinate. This is useful for planning observing sessions, setting up a telescope alignment reference, or simply bookmarking objects you want to revisit.

Because these targets integrate with the same direction and compass tools used for ground navigation, you can point your device toward a saved celestial object and get bearing and elevation guidance. The sky and ground workflows share the same spatial engine.

• Save celestial targets by name or sky coordinates for quick reference.
• Bearing and elevation guidance helps you locate objects in the actual sky.
• Integrates with the same compass and direction tools used on the ground.
• Useful for telescope alignment, observing session planning, and revisiting favorites.

The live Orrery view

The Orrery is a real-time animated model of the solar system rendered directly on your device. It shows the current positions and orbital paths of the planets relative to the Sun, giving you a visual sense of the solar system layout at any moment.

This is not just decorative. Understanding where Earth sits relative to other planets explains visibility windows. When Mars is on the far side of the Sun, it is hard to observe. When Venus is at greatest elongation, it is prominent in the evening or morning sky. The Orrery makes these relationships intuitive instead of abstract.

• Real-time scale model of planetary orbits around the Sun.
• Helps you understand why certain planets are visible at certain times.
• Rendered on device with no server dependency.
• AU scale ruler for reference at the bottom-left corner.

Astronomy alongside navigation and measurement

What makes SIMT different from a standalone sky app is context. The astronomy tools are part of the same toolkit that handles compass navigation, target planning, indoor tracking, AR measurement, local sharing, and Wear OS sync. That means you do not need to switch apps when your evening shifts from hiking to stargazing, or when you want to check satellite timing while navigating to a dark-sky location.

The Astronomer profile in SIMT brings planets, satellites, Moon phases, celestial targets, and the Orrery to the front of the experience. But the other tools remain accessible, so you keep full spatial awareness without fragmenting your workflow across multiple apps.

SIMT is built around the idea that sky awareness and ground awareness are parts of the same spatial need, not separate product categories.

Private and offline by design

SIMT does not send your location, observing history, or saved targets to a server. The astronomy calculations are mathematical operations that run locally, and the results stay on your device. This is a design choice, not a limitation.

For people who care about privacy or who regularly find themselves in low-connectivity environments, this makes SIMT a more dependable astronomy companion than apps that assume constant cloud access. You get the same data quality without the network dependency.

• All astronomical calculations run on device with no server calls.
• Observing history, saved targets, and settings remain private by default.
• Optional Google Drive backup only when you choose to enable it.
• Designed for reliable use in remote, rural, and off-grid locations.

Who benefits from offline astronomy tools

The offline astronomy features in SIMT are useful for a wider range of people than dedicated stargazers. Anyone who spends time outdoors in areas with unreliable connectivity can benefit from having sky awareness on their device without worrying about signal.

• Amateur astronomers who observe from dark-sky sites with no data coverage.
• Campers and hikers who want Moon phase and planet visibility information in the field.
• Photographers planning shots around moonrise, sunset, or planetary conjunctions.
• Satellite enthusiasts tracking ISS passes or Starlink trains from remote locations.
• Travelers who want sky orientation tools that work internationally without roaming.
• Educators and students exploring the solar system layout with the Orrery.

Getting started with SIMT astronomy

SIMT is free, ad-free, and available on Android 9 or later with Wear OS companion support. The astronomy tools are available immediately after installing the app. Choose the Astronomer profile to bring planets, satellites, Moon, celestial targets, and the Orrery to the front, or access them from any other profile when you need sky context alongside other spatial tools.

1. Install SIMT from Google Play.
2. Open the app and select the Astronomer profile, or switch to astronomy tools from any profile.
3. Refresh TLE data once while connected to enable satellite tracking offline.
4. Head to your observing site. Planets, Moon phases, and the Orrery work immediately without internet.

That is all it takes. No account, no subscription, no persistent cloud connection. The sky tools are ready when you are.