The sky above you
Object image
Select something that catches your eye.
Tap a star, planet, or deep-sky marker. Drag the sky to look around.
Altitude through the night
Tap the graph or move the slider to preview the sky. Return to now restores live time. Ten-minute samples; geometric altitude, without refraction, terrain, or weather.
Learn · Black holes
Turn on the Black holes layer or search Sagittarius A*, M87*, or Cygnus X-1. Select a marker, then open details for evidence, estimated mass, distance and sources. Turn off “Above horizon only” to find targets anywhere on the celestial sphere.
What does the marker mean?
A marker shows a known system or galactic nucleus in the sky. Its size is exaggerated. Being above the horizon does not mean the black hole can be seen with your eyes or an optical telescope.
How do we learn about something dark?
We measure stellar orbits, radiation from hot surrounding matter, and radio images of black-hole shadows. Different techniques probe different scales. A shadow image, an optical host-galaxy photo and an artist’s illustration are different kinds of evidence.
Evening observing plan
Build a target list for one evening and location. Suggested times use dark-sky altitude, not weather or telescope limits. Plans are saved in this browser and included in library export/import.
Choose best altitude time or setting first (unfinished targets first, then earliest end of the dark-sky window). Windows use 30-minute samples above 25° during nautical darkness; gaps may occur. Mark observed uses your device’s current time; Log observation opens a separate journal draft. Preview changes the chart to the plan’s saved location and time.
Offline plan photos
Website photo packs are saved privately in this browser on this device. Keep this tab open while downloading. After saving, the sky app and saved photos can work offline. Browsers may remove cached files when storage is needed; check readiness before going offline.
Photos for this plan
Photo packs on this device
Release unused packs to remove their saved device photos, keeping photos used by other packs. Deleting a plan does not release its photos automatically.
Observing journal
Saved in this browser only. Export a backup to move favorites, observations, and plans between computers. Import merges records; it does not sync deletions.