Navigating with Sun, Moon and planets

Knowledge about the apparent movement of the Sun, Moon and planets across the celestial sphere is important for wayfinding. You can estimate position and direction by observing, for example, where the Sun is rising and setting according to the star compass.

The Sun’s path changes through the year

Over the course of a year, the path of the Sun appears to move on the celestial sphere against the background of the fixed stars. Actually it’s the Earth orbiting around the Sun rather than the Sun changing position, but the Sun appears to make a curving path that passes through 12 constellations (collectively called the zodiac). The path it seems to follow is called the ecliptic.

From March to September, the Sun’s path appears to be north of the celestial equator. From September to March, it appears to be south of the celestial equator. The Sun crosses the celestial equator at spring and autumn.

The Sun’s rising and setting points change through the year

Because the position of the Sun in relation to the celestial equator changes over the year, so do its rising and setting points on the horizon. At the spring and autumn equinoxes, the Sun rises due east and sets due west.

At summer solstice – when the tilt of the Earth (23.5°) is most inclined towards the Sun – the Sun in the southern hemisphere rises at ESE (Kāinga Marangai on the star compass) and sets at WSW (Kāinga Whakarunga). In the northern hemisphere, it rises at ENE (Kāinga Tokerau) and sets at WNW (Kāinga Whakararo). This occurs between December 20–23 in the southern hemisphere and June 20–21 in the northern hemisphere. This is when the Sun is at its highest position in the sky.

At winter solstice, the Sun appears to have moved to the opposite side of the celestial equator, with the Earth’s tilt now away from the Sun. In the southern hemisphere, the Sun rises at ENE (Kāinga Tokerau) and sets at WNW (Kāinga Whakararo). In the northern hemisphere, it rises at ESE (Kāinga Marangai) and sets at WSW (Kāinga Whakarunga).

Observing the Sun

Observation of the Sun is done at sunrise and sunset. When the Sun is low on the horizon, its path is narrow and obvious, but as it rises, it gets wider and wider. When it’s too high, you can’t tell where it has risen from and have to use other clues for navigation, such as the shape and direction of the waves.

Phases of the Moon

As the Moon orbits the Earth, its position changes on the celestial sphere just as the Sun’s does. The Moon appears to travel a path similar to the Sun’s through the zodiac constellations but takes only 29.5 days to complete. Its position varies up to 5° on either side of the ecliptic. The amount of light you see (waxing and waning) on the Moon’s surface depends on where the Moon is in relationship to the Sun and to you:

• When the Moon is on the same side of the sky as the Sun – between you and the Sun – you see the unlit side of the Moon and it appears dark (new Moon).
• When the Moon moves away from the Sun, it gradually gains light (moving through the first quarter).
• When the moon is on the opposite side of the sky from the Sun and you are in between, the Moon appears fully lit by the Sun (full Moon).
• When the Moon moves closer to the Sun again, it begins to lose its apparent fullness (moving through the third quarter).

Navigating with the Moon

The Moon rises about 48 minutes later each night at a different position on the eastern horizon from where it rose the night before. Its rising point moves back and forth between Kāinga Tokerau (ENE) and Kāinga Marangai (ESE) on the star compass. Its setting point moves back and forth between Kāinga Whakararo (WNW) and Kāinga Whakarunga (WSW).

Determining the Moon’s rising and setting points along with the rising and setting points of the fixed stars allows the Moon to be used to give direction during the night. The line separating light and dark in the Moon points approximately north and south since the Moon is positioned east or west of the Sun as it arcs through the night sky.

The planets

The planets (initially known as wandering stars) appear to move among the fixed stars – at too fast a pace to be really useful in navigation. Also, they don’t follow consistent orbits, so they aren’t reliable for finding direction. However, they can be helpful in holding a direction because we know they rise broadly in the east and set broadly in the west and are easy to recognise. Venus is particularly bright and recognisable.

The Māori names for the visible planets are:

• Mercury – Whiro
• Venus – Kōpū – also known as Meremere-tū-ahiahi (evening star) and Tawera-i-te-atatū (morning star)
• Mars – Matawhero
• Saturn – Pareārau
• Jupiter – Rangawhenua.