Astera: Sky Map & Astronomy

Open Astera to see a map of the sky above you right now. No sign-up, no ads.

Your sky right now
Point your phone at the sky and the map follows your movements using the phone's orientation sensor. Tap a star or planet for its name, brightness, distance, current direction and altitude, and rise and set times. If it's off-screen, an arrow at the edge points the way. If it's below the horizon, see when it rises next and what the sky will look like then. Faint illustrations, like those in old star atlases, appear behind the constellations so you can see at a glance what shapes the stars form.

The sky at another time or place
Change the date, time, or location to preview the sky. "Simulated observation" stays at the top of the screen, and one tap returns you to your current time and location. All features work without location permission: just choose a city.

Made for the night
Turn on red night mode to make every screen, including settings, search, and your journal, dark red to protect your night vision. A focused observing view hides all menus.

Explore space
Why does the Moon change shape? Are stars in a constellation really close together? When did the starlight you see now begin its journey? Explore these three questions with diagrams you can interact with. Choose "Simple" or "Detailed" explanations. The diagrams also note what has been scaled down or simplified.

Lessons and activities
Open a lesson scene with a fixed location, time, and direction so everyone sees the same sky. Activities follow a sequence: question, prediction, hands-on exploration, explanation, and a summary in your own words. Teacher guides include learning objectives, estimated time, and common misconceptions.

Observation journal
Record the object, time, whether you observed it, and whether you saw it in the real sky or explored it in the app, along with notes. Export entries as text or delete them.

A more realistic sky
Choose a city, suburbs, or dark countryside as your observing site, and the map shows only the stars visible there. The air dims stars near the horizon, and they twinkle more. A bright Moon hides faint stars. Turn on Night Sky Anytime to explore constellations even while the Sun is up. Spread two fingers to zoom in deeply and reveal about 69,000 stars too faint to see with the naked eye, as if looking through binoculars or a telescope. Nebulae and galaxies are shown at their true apparent sizes.

Five languages
Use Astera in Korean, English, Japanese, Simplified Chinese, or Traditional Chinese, with star and constellation names in the selected language. A short guide appears on first launch, and you can revisit it anytime in settings.

Honest information
Star and planet positions are calculated for naked-eye observing and education. Nearby metal or magnets can affect the orientation sensor. The app provides calibration guidance, and you can also adjust the view manually. Stars with large uncertainties in their distance measurements are marked.

Privacy
Your observation journal and location stay on your phone and are never sent to a server. The only outgoing data is error information when the app crashes and requests to retrieve settings that hide incorrect explanations. You can turn off crash reporting in settings.

Sources: Yale Bright Star Catalogue, Hipparcos, d3-celestial constellation data, JPL approximate planetary orbital elements

Recent changes:
Fixed usage statistics not being sent after you agreed to share them. With your consent the app now also sends which features you use, but never search words, the contents of your logs or your location. Star names now sit in open sky instead of under the place and time box, the buttons or the toolbar. The sky clock pauses while the app is in the background to save battery, and the date picker follows the app language even when it differs from your phone's.