Sun and Moon

The plate is the ground around your object seen from above, with north at the top and east on the right, like a map. The white dot in the middle is the object (a post, a person, a tree); the dark wedge is its shadow at the chosen time, drawn to the plate's scale.

The plate automatically rescales to fit the full shadow, with space beyond its tip. The dashed rings show distance from the object, labelled in metres or feet according to Settings. The centre-to-rim distance is shown above the chart. The spacing between rings increases for long shadows, keeping the scale readable.

The Sun sits outside the rim in its compass direction, with a dashed line to the object: the shadow always points the opposite way. The blue dotted curve traces the shadow tip through the chosen day, with hourly dots and labels where space allows. Parts of that daily path can lie outside the current scale, particularly near sunrise and sunset; the shadow at the selected time fits in full.

Pick any date and time at the top, past or future; Now returns to the present. The headline repeats the time and the place.

Times are the chosen place's local time, so enter the time as it is on the clock there. With the device location they are your phone's.

The row under the headline is the place: your device location by default. Tap Change to search for a city, address or landmark, drop a pin or type coordinates; Use GPS goes back to where you are. You can also tap the map to move the point. The place is shared with the rest of the app.

A satellite map of the chosen spot with the shadow drawn to scale on the ground and a dashed line toward the Sun. Short shadows are only a few pixels long until you zoom in. The buttons return to your location, show the map's north and its scale.

Slide from 0.5 to 10 m (about 1.6 to 33 ft) in half-metre steps. The shadow is in proportion: double the height, double the shadow. Lengths follow your units in Settings (feet with imperial units).

Shadow length is the object's height divided by the tangent of the Sun's height. It points directly away from the Sun: the Sun's compass direction plus 180°. Length to height says how many times longer than the object the shadow is: above 1 the Sun is lower than 45°, below 1 higher.

Shadows are longest at sunrise and sunset and shortest at solar noon, when they point due north in the northern hemisphere and due south in the southern (between the tropics they can point either way).

The Sun's position is calculated on your phone with the SwiftAA library (Meeus's Astronomical Algorithms). Place search, place names and the map come from Apple Maps.

Results assume flat, level ground and a thin, upright object. Slopes, walls and the width of the object change real shadows; below about 5° of Sun the shadow becomes extremely long and is easily broken by terrain.

The ribbon in the middle is the Sun's height, from 8° below the horizon at the bottom to 9° above at the top, painted with the light each height gives. The Sun climbs the ladder in the morning and comes back down in the evening, so each line has two times: the morning one on the left and the evening one on the right.

Read across a line to see when the Sun passes that height. For example, the left time on the 0° line is sunrise and the right time is sunset. On today's date a golden dot on the ribbon's left or right edge shows where the Sun is now, on the morning or evening side.

The ribbon and the dots next to each window use the same colours.

Warm golden-red light from a low Sun, soft and directional, with long shadows that bring out texture. Good for portraits (a warm, flattering glow on skin), landscapes (dramatic shadows and textures) and architecture (warm light on building materials).

It is longest in winter and at high latitudes, where the Sun climbs and sinks at a shallow angle, and shortest near the equator.

The Sun is below the horizon and the sky fills with an even, deep blue; the light is shadowless and short-lived. Good for cityscapes (lit buildings against a blue sky), seascapes and any calm, quiet scene.

The two sections list each window's start and end time and how long it lasts, with sunrise and sunset between them. When today is chosen, the line under the ladder says which window you are in now or which comes next.

Far north or south the Sun may not pass every threshold: in summer it may never sink to 4° or 6° below the horizon, in winter never climb to 6° above. Those times show a dash and the section says so.

Calculated on your phone from the chosen place and date with SwiftAA (Jean Meeus's Astronomical Algorithms): the Sun's height is sampled through the day and each threshold crossing refined. Times are the chosen place's local time and assume a flat, clear horizon; hills, buildings and cloud change what you actually see.

At the top is the next eclipse you can see from here (or, if none is visible, simply the next one), drawn as it looks at its deepest from your location. Next to it: how many days away it is, its name and how much is covered.

For a solar eclipse the dark disc is the Moon passing in front of the Sun; for a lunar eclipse the red-brown shading is the Earth's shadow (the umbra) on the Moon, and a faint grey is the outer shadow (the penumbra). The size of the overlap follows the magnitude. Each eclipse below has a small version of the same drawing; faded drawings are eclipses you cannot see from here.

Under the drawing, the coming 24 months from today, with each new year marked. Every eclipse is a dot on its date; the ringed dot is the one drawn above.

The heading is the eclipse's name. Under it: the date, whether you can see it and as what, and how many days away it is. A green dot means some of it happens above your horizon; a grey dot means none of it does.

The type seen from here can be milder than the type worldwide: a total solar eclipse is only total along a narrow path and partial for hundreds of kilometres either side.

For eclipses you can see: begins (first contact), maximum (greatest eclipse at your place) and ends (last contact), in the chosen place's local time on that date (it may differ from today's if summer time changes in between).

The line shows the whole eclipse from beginning to end, with the white dot at maximum. When only part of it happens above your horizon, the heavier stretch is the part you can see and Above your horizon gives its times; the footnote says whether the Sun or Moon rises or sets during the eclipse. Deepest you can see is shown when the maximum itself happens below the horizon.

The umbral phase of a lunar eclipse is the easy-to-see part, when the Earth's full shadow bites into the Moon; the totality or annularity phase gives the time and length of the total or ring phase.

Magnitude is the fraction of the eclipsed body's diameter that is covered at maximum (above 1 means totality). Area covered is the fraction of its disc, which is what you notice. A penumbral lunar eclipse only dims the Moon slightly, so no coverage is quoted for it.

Height at maximum is the Sun's or Moon's angle above your horizon at the moment of greatest eclipse; below 0° it is under the horizon.

Never look at the Sun during a partial or annular solar eclipse without certified eclipse glasses or a proper solar filter. Lunar eclipses are safe to watch with the naked eye, binoculars or a telescope.

The list and the local circumstances are computed by the iCaelum service from NASA JPL's DE421 ephemeris (via Skyfield) for your coordinates, and refreshed once a day or when you move more than about 25 km.

If the list can't be loaded, check your connection and tap Try again.

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.