Stargazing

Switch Planets, Stars, Sun and Moon independently. Sky finder remembers your layers and star brightness setting. Find lists objects alphabetically and searches all seven other planets and 5,041 stars down to catalogue magnitude 6; selecting an object turns on its layer and includes its brightness. Other objects in enabled layers remain visible when you select a target.

The settings button offers Bright, More and All stars. A selected star remains included if you later lower the brightness limit. Brighter stars get larger points. Names prioritise the selected object, planets and bright named stars; other stars remain points to keep the view readable. Tap a point or use Find to select it.

Select an object for its true bearing, height and turn or tilt guidance. Objects below the horizon remain searchable, but are not drawn over the ground. The thin gold line marks a level horizon at 0° height; it does not trace buildings, hills or trees. True north and working camera tracking are required before the overlay appears.

Compass errors can move every marker. Away from magnets and metal, select a familiar bright star, planet or the Moon at least 5° above the horizon. Centre the real object in the reticle, hold steady and tap Align. This corrects horizontal compass error; it does not identify the object for you. A wrong identification gives a wrong alignment.

Find, settings and this guide keep tracking running to preserve your alignment. Switching apps or locking the phone pauses the camera; check the marker when you return and align again if needed. Reset alignment restores compass north. Leaving Sky finder starts a new visit without the old correction. If a camera failure prevents the session from continuing, a message asks you to reopen and align again.

A marker means the calculated position is above the horizon, not that an object can be seen. Daylight, clouds, glare, terrain, buildings and light pollution affect visibility. Uranus and Neptune usually need optical aid. Dimmer stars are best explored under a dark sky.

Hollow rings mark calculated positions and leave their centres clear so you can compare them with real points of light. The selected object has a larger ring, with its label placed clear of the centre. Stars are coloured approximately from their catalogue B−V colour. Ring sizes are symbolic, not the objects’ angular sizes. Camera exposure and the phone’s sensors limit the real scene, especially at night.

The live camera sky always uses the phone’s physical location, even if another planning place is selected elsewhere in iCaelum. A recent location fix and true north are needed. Allow camera and location in iOS Settings if requested. With no camera access you can still browse positions after location is available.

Star and planet calculations work offline. Images are not recorded, recognised or uploaded. The screen stays awake while Sky finder is open, including its panels. Normal auto-lock returns when you leave or switch apps; you can still lock the phone yourself. Camera, heading and continuous location requests stay active through Find, settings and this guide, and pause when you leave Sky finder or the app becomes inactive.

Planets use SwiftAA / AA+ (Meeus and VSOP87), with light-time, apparent coordinates and observer parallax. Star coordinates use ESA Hipparcos I/239 via CDS VizieR, with proper motion from epoch J1991.25, precession from the ICRS/J2000 frame, annual aberration and nutation. Proper names use the IAU Working Group on Star Names catalogue (2022-04-04 snapshot). Unnamed entries use their HIP numbers.

Height includes an approximate standard-atmosphere refraction correction. Real refraction varies most near the horizon. Earth rotation uses UTC as an approximation to UT1; ephemerides use terrestrial time with a bundled leap-second table. Sensor and alignment errors normally exceed these numerical approximations. This is an exploration aid, not a precision pointing instrument.

Never look directly at the Sun or through an optical viewfinder. Use the phone’s screen only.