Hiking

Daylight dial#

The daylight available for an outing.

The big figure answers the question that matters on a hike: how long you have. Today it counts down the daylight left until sunset, then the last light left until civil dusk; before sunrise it counts down to sunrise, and after dark it gives tomorrow's first light. It updates every minute.

On another day it shows the total daylight, from sunrise to sunset. The line under it gives last light and how long after sunset it comes.

Daylight and sun events#

Sunrise, noon, sunset and daylight duration.

Daylight is the time from sunrise to sunset, the basis for planning the length of a hike. Sunrise and sunset come with their compass directions, so you know which slopes catch the first and last sun. Solar noon is when the Sun is highest, with that height.

Sunrise and sunset are when the top of the Sun touches a flat, sea-level horizon. In a valley the Sun disappears behind the ridges earlier; on a summit you see it longer (see the altitude adjustment).

Twilight and last light#

The light available after sunset.

Last light is the end of civil twilight, when the Sun is 6° below the horizon. Light can fade earlier under trees or in poor weather; civil twilight does not guarantee that a trail or map is visible. Plan to be off exposed or difficult ground by then.

First light is civil dawn, the morning equivalent. Nautical twilight ends when the Sun is 12° below: the horizon is no longer visible. Astronomical twilight ends at 18° below: the sky is fully dark.

Route sun and shade#

Estimate light along a timed waypoint route.

Tap up to sixteen waypoints in walking order, starting at your selected planning location. The map connects straight legs; it does not find trails or assess whether a route is passable. Undo removes the last point and Reset starts again.

Choose departure, walking speed, total ascent and breaks. Estimated duration is distance divided by speed, plus one hour per 600 metres climbed and your breaks. Time is spread uniformly over the route; steep sections, descents and stops may move the actual exposure windows.

The coloured strip follows your timed walk, with minutes in direct sun, modelled shade, twilight and dark. A measured skyline angle models a uniform surrounding ridge; zero means an open horizon. To measure it, stretch your arm out: an upright fist is about 10°, three fingers about 5°, one finger about 2°; count from the level horizon up to the skyline toward the Sun's path. It does not download terrain or tree cover. Low Sun ahead flags potential glare. Sampling is every five minutes for normal walks; allow a generous margin rather than treating twilight as guaranteed visibility.

Find your campsite light#

Compare sunlight at three campsites.

Tap the map to compare up to three candidate sites. Enter a measured skyline angle for each site, then compare morning sun (06:00–12:00) or less evening sun (15:00–21:00), in the chosen place’s local time. All sites use the selected date; the dial shows a full day with midnight at the top and noon at the bottom.

The ranking compares potential direct sunlight only. Ties receive the same rank. Evening preference includes periods after sunset; a dark site is not necessarily sheltered. The first-sun time and totals use five-minute samples, approximately ±5 minutes at transitions. Cloud, canopy and directional ridges can change the result.

Confirm camping permission and inspect drainage, overhead branches, wind and flood exposure in person. These light comparisons do not certify a site as safe or available.

Emergency signal and location#

Physical device coordinates and a visual SOS signal.

This card always shows your physical device GPS, independently of a chosen planning location. Accuracy and the recorded time accompany the coordinates. A fix older than two minutes is labelled last known; refresh before sharing. The system share sheet lets you choose a recipient or copy the position; iCaelum does not automatically send it.

The SOS screen starts steadily lit. Choose Screen or Flashlight. Screen flashing and the rear flashlight repeat three short, three long, three short Morse signals only after you press Start. Flashlight mode keeps the display dark; unavailable hardware or overheating is reported with Screen as a fallback. Screen mode increases brightness; auto-lock is temporarily disabled while it is open; closing or leaving the app restores both. Manually locking the phone stops signaling, including the flashlight. Returning does not restart flashing. No distress alert is transmitted.

Use the iPhone’s Emergency Call slider to contact emergency services. Apple’s satellite SOS, where supported, is managed by iOS rather than this screen. The card links to Apple’s instructions.

The Sun’s position#

Bearing and altitude at the selected time.

Where the Sun is at the moment (or at the same time of day on another date): the arrow points toward it with north at the top, as on a map. Direction is a compass bearing from true north, height is degrees above the horizon. Use it to anticipate shade, sun exposure and glare.

Altitude adjustment: from up high you see over the curve of the Earth, so the Sun appears earlier in the morning and stays longer in the evening. iCaelum takes the elevation your phone reports, works out how far below level the horizon lies (the dip) and converts it at about four minutes per degree. It applies only with an open view to a distant horizon, and is approximate away from the equator.

Moon for night visibility#

Phase and the Moon’s position for the outing.

The Moon drawn as it looks on this date, its phase and the share lit, with moonrise and moonset. A bright Moon high in the sky lights open ground and snow well; under trees and with a thin crescent it gives little help. It is never a substitute for a headlamp.