Stellarium is a free, open-source planetarium for Windows, macOS and Linux. It calculates and displays the sky from a chosen observing location and time, letting you identify stars and planets, explore constellations and prepare telescope observations. Its three-dimensional sky combines celestial positions with a horizon, atmosphere and adjustable viewing conditions.
Location, time and viewing conditions
The observer’s position determines which part of the sky appears above the horizon. In Stellarium, you can choose a city, select a point on the map or enter latitude and longitude, then save that location for later sessions. Changing the date and time recalculates the scene for that place, so the same sky can be examined before an observing session or at a historical date.
Time controls let the simulation run normally, move faster, pause or run backwards. Accelerating it makes the rising and setting of objects visible without waiting through the night. You can pan around the horizon and zoom into a smaller region while following that movement, then return to the current time.
The atmosphere and light pollution affect the simulated view. A brightness slider or a Sky Quality Meter reading sets the light pollution level, while a limiting magnitude controls whether faint stars appear. These settings let the view concentrate on stars visible to the unaided eye or include fainter targets for optical observing.
Finding objects by name or position
Stellarium’s search window finds celestial objects by name and centers the selected result. A separate position entry accepts coordinates when the target is a location in the sky rather than a familiar name. Optional online SIMBAD searches extend name lookup beyond the local catalogues; the program can point to the returned coordinates even when it has no local object to draw there.
The sky includes planets and their moons, stars, star clusters, galaxies and nebulae. You can enable particular deep-sky catalogues or object types to control the selection available in searches and observing tools. Coordinate grids, the celestial equator and the ecliptic provide reference lines around those objects, with adjustable colors for separating the overlays.
Planning observations with Stellarium
The What’s Up Tonight tool builds a list for the selected date and location. Filters narrow it by object category, brightness and the portion of the night you intend to observe, such as the evening or the hours before dawn. Choosing an entry places it in the sky view, connecting the list to its position above the horizon.
For a moving target, Stellarium can calculate an ephemeris: a sequence of predicted positions and brightness values between chosen dates. A time step controls the spacing, and markers plot those positions against the sky. Separate calculations give rising, meridian transit and setting times, or find events such as planetary conjunctions and oppositions. Tabular results can be exported to CSV or Excel files.
Observing lists retain selected objects for another session. They can also preserve the time, location, landscape and field of view, so a list can hold a particular conjunction or eclipse rather than an object alone. Lists can be exported and imported on another computer.
Field-of-view previews
The Oculars plugin previews how much sky fits through a telescope and eyepiece combination. You enter equipment properties such as telescope focal length and aperture, then choose the eyepiece’s focal length and apparent field of view. Switching combinations changes the simulated field, helping establish whether an extended target fits within it.
Camera sensor overlays provide a corresponding framing view for astrophotography. Telescope and sensor selections determine the area covered, while orientation and image-flip controls account for the equipment arrangement. Telrad circles offer another reference: concentric angular guides that help relate a target to nearby stars when pointing manually.
Pointing a mount with TelescopeControl
With the TelescopeControl plugin, Stellarium can send a GoTo command for a selected object to a compatible motorized mount and display the mount’s reported pointing position. Connections can use supported devices directly or work through a telescope server, including network arrangements.
The mount needs its location and alignment set before connection. Available commands depend on the device; some also support synchronization or stopping a slew. General satellite tracking is not provided by this plugin, apart from its RTS2 support.
Sky cultures and scripted presentations
Constellation lines, names and illustrations can be changed through sky cultures, allowing different traditions’ patterns to be examined on the same stars. Landscapes supply the surrounding horizon, and a landscape with location data can also set the observer’s position when that option is enabled.
Stellarium scripts use JavaScript to arrange a repeatable sequence of simulation times, scene movements and display changes. This supports an astronomy presentation that moves between selected views instead of relying on manual navigation throughout. Fish-eye and spherical-mirror projection options extend that presentation to suitable planetarium dome setups.
