Skip to content

November Sky Watch: Using the Star Compass in Oceanic Wayfinding

by Imiloa Astronomy Center on November 2nd, 2017

By Chad Kālepa Baybayan & Emily Peavy, ‘Imiloa Astronomy Center of Hawai‛i

Using the Star Compass in Oceanic Wayfinding

In our first Skywatch column last month, we discussed how an ability to read the night sky contributes to the three essential functions of oceanic wayfinding: (1) orienting the direction of a vessel, (2) determining the vessel’s position at sea, and (3) making a successful landfall. Today we will further explore the Star Compass, the tool used by modern navigators on traditional sailing canoes such as the Hōkūle‘a.

The Star Compass is designed as a circle whose edge represents the visual horizon, where the sky touches the land or the sea. To use it, you position yourself in the center of the circle, and begin by establishing the first two cardinal directions: Hikina, east, for the arriving horizon, and Komohana, west, for the entering horizon. With your back to Hikina, your body faces Komohana, and if you extend both arms from the sides of your body, your right arm points toward ‘Ākau, meaning north and right, and your left arm toward Hema, meaning south and left. With Hikina-Komohana and ‘Ākau-Hema intersecting at 90˚ angles, the circle is thus divided into four quadrants.

Each quadrant is named for the winds that typically blow from that quarter. Between north and east is the quadrant Ko’olau; between east and south is the quadrant Malanai; between south and west is the quadrant Kona; and between west and north is the quadrant Ho’olua. Seven houses between each of the four cardinal directions divide the circle evenly. Beginning from either side of Hikina and Komohana and moving towards ʻAkau and Hema are the houses Lā, ʻĀina, Noio, Manu, Nālani, Nāleo, and Haka.

The star compass works like a mirror with the Hikina side reflecting the Komohana side. It also reflects across the quadrant, so Koʻolau reflects with Kona and Malanai reflects with Hoʻolua, and vice versa. The compass works this way: if a star rises in the house called ʻĀina Koʻolau, it climbs out of the arriving horizon, Hikina, arcs upwards until it crosses the meridian (the imaginary line that runs between ʻĀkau and Hema) and begins its descent towards the entering horizon, Komohana, before re-entering the horizon in the same house it arose, ʻAina Hoʻolua, only on the opposite side of the compass.

As objects viewed from the perspective of earth, stars are identified with the hemisphere in which they rise and set and move in parallel tracks across the compass. Stars rising from the northern hemisphere set in the northern hemisphere. In the same manner, wind and swell patterns can be envisioned as moving from quadrant to opposite quadrant in the same hemisphere within the star compass. If a swell or wind moves into the compass from the house Manu Koʻolau, it raverse the center of the compass and exits the opposite quadrant in the house Manu Kona.

The beauty of the Star Compass is its natural symmetry and reflective quality, allowing the navigator to use nature’s clues to determine direction.

 

Evening Observing

Through November the sun will set around 5:40 pm, and it will be completely dark by 7pm, a ripe time for astronomical observations. At dusk, several planets start to become visible. As the closest planet to the Sun, Mercury will always set just after the Sun has set, so throughout the month you can catch a glimpse of Mercury during dusk as it appears to chase the Sun into the western sky. On November 23rd, Mercury will be at a position known as greatest eastern elongation, marking its furthest position from the sun in our sky. This will be the best night to view Mercury, though it will still be faint and setting at 7 pm.

In the west, just after sunset, you can see the ringed planet, Saturn, as it sets early in the evening (by mid-November it will set just before 8 pm). Saturn often appears to be a bit faint in our sky, but it will still be one of the first objects to become visible at nightfall. A small telescope will enable you to catch a glimpse of Saturn’s distinctive rings.

 

Through mid-to-late November, the spectacular Leonid meteor shower will scatter our sky with shooting stars. The Leonids are debris from the tail of the comet Tempel-Tuttle, a periodic comet which last swept through Earth’s orbit in 1998. The peak of the shower will occur on Friday, November 17th, when you should be able to see at least 10-15 meteors each hour.

Rising in the East will be the distinctive star cluster of Makaliʻi, or the Pleiades. This stellar open cluster stands out with its 7 brightest stars clearly visible to the naked eye. The stars in the cluster were all born from the same nebula about 100 million years ago. As these stars are around the same age, the cluster can be used as a laboratory for the study of stellar evolution.  Makaliʻi is also used as a marker for the Makahiki season, the fall harvest celebration in the Hawaiian calendar when the chiefly class collected tribute from local communities and athletic competitions took place.

 

Early Morning Observing

Early risers will get a different perspective of the sky.  Since the sun rises at 6:30am the sky will still be mostly dark until about 6am. Look for the rusty red planet, Mars, as it rises in the East at about 4am. The red color of Mars makes it stand out against the background of stars; Mars gets its red color from the iron-oxide present in its soil.

Just before the sun rises, the bright shape Kaheiheionākeiki (Child’s Cat’s Cradle), which shares the same stars as Orion the Hunter, will be visible in the western sky. The first star to rise in Orionʻs belt, also known as Nākao, is Melemele (Mintaka); it rises exactly east and is used as a marker for the Star Compass house of Hikina. Beneath Nākao, observers can look for the gray fuzziness of the famous Orion Nebula.

 

Moon Phases for November

Full Moon: 7:23 pm HST, Friday, November 3rd

Last Quarter Moon: 10:37 am HST, Friday, November 10th

New Moon: 1:42am HST, Saturday, November 18th

First Quarter Moon: 7:03 am HST, Sunday, November 26th

The Moon’s phase is determined by its position in relation to the Sun and the Earth. The designations of Full, Last Quarter, New and First Quarter refer to specific orientations of the Moon, Sun and Earth. Listed above are the exact times the Moon will be in the precise orientation; however the Moon will not necessarily be visible in Hawai‘i’s sky at the specific time.  As the Moon is incredibly bright in the sky, the best time to do stargazing without its interference will be the week around New Moon (November 18th).

Chad KālepaBaybayan (kbaybayan@imiloahawaii.org) serves as Navigator-in-Residence and Emily Peavy (epeavy@imiloahawaii.org) as Planetarium Technician Support Facilitator.

 

Comments are closed.