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October Sky Watch: The Stars Above Hawai‘i

by Imiloa Astronomy Center on September 25th, 2017

‘Imiloa is excited to announce that we are now regular contributors to the Honolulu Star-Advertiser! ‘Imiloa’s Sky Watch shares the upcoming month’s sky chart and highlights of the night sky, and will appear in the newspaper on the last Sunday of each month. Sky Watch is written by Kālepa Baybayan, navigator-in-residence, and Emily Peavy, planetarium technician and support facilitator at ‘Imiloa. 

 

A keenly developed ability to read the night sky helped early Polynesians find their way from island to island across the Pacific, and ultimately to Hawai‘i. Under the leadership of the Polynesian Voyaging Society, modern Hawaiian voyagers have rediscovered this knowledge and continued to develop and share it with a broader community. The recent completion of the three-year Mālama Honua Worldwide Voyage by the iconic voyaging canoe Hōkūle‛a underscores the timeless relevance of this indigenous system of celestial navigation.

 

A First Look at Oceanic Wayfinding

Traditional oceanic wayfinding, or non-instrument navigation, needs to perform three essential functions: (1) to orient and set direction for the vessel, (2) to identify the vessel’s position at sea, and (3) to make landfall. The tool used by modern-day navigators aboard the Hōkūle‛a is the Hawaiian Star Compass.

A sidereal (“star”) compass, the modern Hawaiian Star Compass is based upon traditional models of orientation and direction setting. The framework for the star compass is a circle whose edge represents the visual horizon, where sky touches land or sea. The user, at the center of the circle, is represented by the image of a bird in flight, reinforcing the concept that a bird is never lost, but always guided by an internal compass that leads to distant landfalls.

The circle is divided into four principal directions that intersect at 90˚ angles, east-west and north-south. The primary celestial body used to establish direction in the star compass is our daytime star, the sun. The sun travels a yearly cycle, rising north of east during our northern hemisphere summer, and then rising south of east during our winter.

The Hawaiian word for east, Hikina, means “to arrive” and references the horizon where stars first arrive and begin their nightly climb into the sky. As they move across the sky and transit the meridian they begin their descent towards the west, reentering the horizon to disappear from sight. The Hawaiian word for west, Komohana, means “to enter.” With the Hawaiian Star Compass these are the first two cardinal directions to establish: Hikina, “to arrive” and Komohana, “to enter.”

A bird flying with its tail pointed towards Hikina, or east, would have its beak facing Komohana, west. Its right wing would extend towards the edge of the circle we call ‘Ākau, north, and its left wing would point to Hema, south. An imaginary line drawn between north and south, the meridian, is the boundary between eastward-rising and westward-descending stars.

 

The compass circle is divided into 32 segments called star houses, each of which occupies an 11.25˚ arc of the circle. To enable the setting of course and direction, the navigator memorizes the houses where key stars rise and set. The star compass diagram above includes the names of the first four star houses; remaining names will be shared in future articles.

 

Evening Observing

The hour of 8 pm is a great time to do stargazing, since it is usually nice and dark but not too late. Throughout October, Kahuinakoluhoʻokele (The Navigator’s Triangle) will be high and bright in the sky at this time. Comprised of three stars–Humu (Altair), Keoe (Vega), and Pira‘etea (Deneb)–the triangle stands out against the band of our Milky Way galaxy. These three stars symbolize the Pacific island groups that define Polynesia: Humu representing Aotearoa (New Zealand), Keoe representing Rapanui (Easter Island), and Pira‘etea representing Hawai‘i. The triangle also forms one part of the Hawaiian star family Mānaiakalani (Maui’s fishhook).

In the northeastern part of the sky, observers can see the faint Andromeda Galaxy. First locate the bright “W” shape of ‘Iwakeli‘i (Chief Frigate Bird) (Cassiopeia) and look about 15 degrees south of its lowest, brightest star. To the naked eye, the galaxy looks like a small blurry smudge, but keep in mind this is the farthest that humans can see with the naked eye–about 2.5 million light years away! Andromeda is the closest galaxy to our Milky Way. Gravitationally the two galaxies are moving closer together and are actually set to collide in a few billion years.

Throughout October the dynamic planet Saturn will be faintly visible in the southeastern sky in the early evening. Through even a small telescope, observers can spy Saturn’s famous rings. These rings were observed in great detail by NASA’s Cassini Spacecraft, which finished its 13-year long orbit just ten days ago, after groundbreaking research supported in part by observations performed at Hawai‛i-based telescopes on Maunakea. Saturn will set just before 10:30 pm at the start of October, but as the month goes on, it will set earlier and earlier, around 8:30 pm by October 31.

Starting in mid-October, the Orionid meteor shower will decorate our skies. This annual meteor shower occurs from October 16-27 and is made up of debris left from Halley’s Comet. At its peak on October 21, it will produce about 20 meteors, or shooting stars, per hour.

 

Early Morning Observing

With the sun rising just after 6 am in October, the hours of 4 am and 5 am will be nice and dark for early-rising observers. In these morning hours the shape of Kaheiheionākeiki (Child’s Cat’s Cradle), which shares the same stars as Orion the Hunter, will be high up in the southern part of the sky. The first star to rise in Orion’s belt is known as Melemele (Mintaka); it rises exactly east and is used as a marker for the Star Compass house of Hikina.

Before the Sun rises, the bright planet Venus and the red planet Mars will rise in the east. At the start of the month these two planets will appear close together and will even be in conjunction on October 5, with a separation of less than 1 degree. At the start of the month both planets will rise just before 5 am; then Venus will rise later and later, and the planets will slowly move apart. By month’s end, Mars will rise around 4 am, but Venus will not rise until an hour later, at about 5 am.

The planet Venus is often referred to as “the morning star,” as it is one of the last objects to fade from our sky at daybreak. Venus’ thick atmosphere reflects a significant amount of light, making it one of the brightest objects in the sky. Through a pair of binoculars or a telescope, observers can see Venus waxing and waning, just as the Moon does. This happens because Venus is closer to the Sun than Earth is, and thus exhibits constant shifts in the phases of its daytime and nighttime sides as it orbits the Sun. At the beginning of the month observers will be able to catch a sliver of Venus’ night side; this sliver will slowly get smaller and smaller as the month goes on.

Mars is famous for its rusty red color in our night sky; its soil is packed full of iron-rich minerals which have oxidized, or rusted, over time. Unfortunately, Mars doesn’t look particularly remarkable through a simple telescope. However, we do get fantastic images from the NASA orbiters and rovers which are carefully studying the unique contours and history of the red planet.

 

Moon Phases for October

Full Moon: 8:40 am HST, Thursday October 5

Last Quarter Moon: 2:25 am HST, Thursday October 12

New Moon: 9:12 am HST, Thursday October 19

First Quarter Moon: 12:22 pm HST, Friday, October 27

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 Moon 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 (October 19).

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