Stellarium

What Stellarium shows

Stellarium renders the night sky as a realistic three-dimensional scene rather than a printed chart. It places stars, planets, the Moon, deep-sky objects and artificial satellites at their computed positions for any date, time and location on Earth, and it draws them over a photographic landscape with the atmosphere, twilight glow and light pollution simulated. Constellation lines, boundaries, art work and labels for many sky cultures can be layered on top, and the zoom range runs from a whole-sky fisheye view down to a magnified field that matches what a particular eyepiece and telescope would show.

How an observing session runs

The first run asks for a location and saves it, after which the sky is always correct for that place until you change it. From there the workflow is mostly navigation: open the search window, type part of an object name, and the view swings to it with the object centred and identified. Time is fully controllable, so you can rewind to see a conjunction that already happened, run the clock forward to find when a planet rises, or freeze it while you compare two dates. The bottom toolbar toggles the ground, atmosphere, constellation lines, labels, grids and the equatorial or azimuthal coordinate systems, which lets you strip the display down to bare sky when the screen light matters.

For practical observing, the ocular view plugin shows the field of view of your actual equipment, so you can judge whether a target fits in the eyepiece and how it is oriented with respect to nearby stars. The telescope control plugin connects to a mount over ASCOM on Windows, or over INDI or a network protocol, and can slew to whatever is selected, while the satellites plugin tracks catalogued spacecraft after an orbital data update. Observing lists, bookmarks and screenshot capture round out a session, and the whole configuration is stored in a text file that can be copied between machines.

Settings, downloads and limits

The default installation carries a star catalogue large enough for naked-eye and binocular work, but the program can download much deeper catalogues and additional landscapes, which run into hundreds of megabytes and, for the largest sets, several gigabytes. Rendering is GPU intensive: a machine with weak integrated graphics will drop frames when the atmosphere, many labels and deep catalogues are enabled at once, and the display is best tuned by lowering the magnitude limit rather than by reducing the window size. Positions are computed for pointing and teaching, not for precision astrometry, and satellite tracking depends on orbital data that must be refreshed from time to time. There is no image capture, guiding or stacking: Stellarium plans and points, it does not photograph.

Who should choose something else

If your goal is printable finder charts with precise star magnitudes for a deep-sky marathon, a dedicated charting program produces better paper output. If you are automating an imaging rig with plate solving, focusing and sequence capture, session automation software is the right layer. And for research-grade ephemerides or occultation timing, professional tools and services are more appropriate. Stellarium remains the most attractive way to learn the sky, prepare a session and show the sky to an audience.