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Pepeluali (February) Sky Watch

by Imiloa Astronomy Center on January 28th, 2018

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

To navigate the seas using only the stars and other clues from nature, one needs to learn three essential functions: (1) orienting the canoe, (2) determining the canoe’s position at sea, and (3) making landfall.

 

In previous articles, we have taken readers on a wayfinding journey, starting off with using the Hawaiian star compass to orient the canoe. To recap, unlike the conventional magnetic compass, the star compass serves as a conceptual framework for the navigator.  By locating the sun, moon, stars, wind, and swells along the canoe’s perimeter as bearing points on the star compass, the navigator derives directional clues which orient the canoe to the horizon. Once determined, the navigator needs to commit the information to memory for the duration of the voyage since the star compass is non-magnetic; it is, rather, a mental device that orients and determines direction for a canoe at sea. Suffice it to say, wayfinding is a cerebral process that engages the intellectual capacity of the navigator.

 

For this column, we will address the second skill set, determining the position of a canoe at sea. The route between Hawaiʻi and Tahiti offers the best example for explaining how position can be determined. Tahiti is approximately 2,250 nautical miles from Hilo and lies in the direction of Nāleo Malanai, south-southeast on our star compass. The general heading to Tahiti lies in a north-south direction and position can be determined based upon nautical miles or degrees of latitude traveled.

 

The process for determining nautical miles traveled is called dead reckoning and can be expressed as an algebraic equation: S (speed) x T (time) = D (distance). Thus, a canoe traveling at 5 knots (speed) for 12 hours (time) would have traveled 60 nautical miles. On board Hōkūleʻa, speed is determined by counting timing marks (bubbles or objects on the water) as they float from the front ʻiako (cross piece) to the back ʻiako, a distance of 42.2 feet. The navigator needs to memorize a timing cadence (“one-one thousand, two-one thousand, three-one thousand,” etc.) so that he/she can be accurate in measuring a timing mark.

 

A table is then created to allow the crew to compute speed quickly: 3 seconds = 8.5 knots; 4 seconds = 6.5 knots; 5 seconds = 5 knots; 6 seconds = 4 knots. The navigator estimates speed by dividing the number 25 by the amount of seconds it takes a timing mark to float 42.2 feet, front ʻiako to back ʻiako. For example, 25 divided by 5 seconds = 5 knots of speed. The navigator checks the speed throughout the day and computes the distance traveled at the end of a 12-hour cycle, sunrise or sunset. This process is repeated and recorded for the entire length of the journey until landfall is made.

 


The other way to determine latitude is through various techniques involving the measurement of stars when they are at meridian, the highest altitude that a star reaches as it crosses from Hikina (East) to Komohana (West).  One technique is using your hands; palms facing out or in. When using palms facing out, the thumb rests on the horizon and the index finger above it. You should be able to measure an altitude of about 20˚ degrees.  With the palms facing in technique, the lower straight line of the hand rests along the horizon and the thumb extended above it. You should be able to measure an altitude of 10˚ degrees.

 

 

 

 

 

 

 

 

The latitude between Hawaiʻi and the equator can be computed by estimating the altitude of Hōkūpa‘a (Fixed Star), also widely known as “the North Star” or Polaris, which is positioned close to celestial ‘Ākau (North). In Hawaiʻi, by using the palms out position, Hōkūpa‘a should be one-hand span, 20˚ degrees, above the horizon . If measuring Hōkūpa‘a at 10˚ degrees altitude, one should be at 10˚ degrees north latitude. However, as one approaches the equator, clouds on the horizon will obscure Hōkūpa‘a. It will also not be visible in the sky south of the equator. In both of these situations, other stars will need to be used.  It is important to note that varying human hand sizes, will affect the determination of altitude.  Wayfinding is an approximation using visual clues and human senses.  Try finding Hōkūpa‘a tonight and measuring its altitude using your palm out position; depending on the size of your hand, you should get a measurement of one-hand span above the horizon.

The third skill set (making landfall) will be addressed in next month’s column.

February Night Sky
Before introducing the February sky, it is noteworthy to highlight an exciting event in the early morning of Wednesday, January 31st. That day will mark the second full moon of the month, which is often referred to as a “blue moon.” The moon will also happen to be in a unique position on its orbit known as perigee, where it is closest to Earth. When the moon is full at the same time it’s at perigee we often refer to it as a “supermoon”.  

 

Additionally, in the early morning hours of Wednesday, Jan. 31st, the moon will pass through the Earth’s shadow in a lunar eclipse, often called a “blood moon”.  So, be on the lookout for a “super-blue-blood moon” from the evening of January 30th to the early morning of January 31st.  In Hawai‘i, the eclipse will start around 2 am. As the moon starts to get redder, totality will begin just before 3 am with maximum eclipse occuring at 3:30 am. The total eclipse will end at 4 am and the moon will be completely out of the Earth’s shadow by 5 am.

 

As aforementioned, Hōkūpa‘a (the North Star) is famous across the northern hemisphere; many children in scouting organizations are taught how to find it in the sky using the Big Dipper. However, there is a common misconception that it is the brightest star in sky. There are actually about forty-seven brighter stars in the whole night sky. The significance of Hōkūpa‘a is that it is on the rotational axis of the Earth, which means the star will always appear in exact North while you are in the Northern hemisphere. Regardless of seasons, the star remains in the same position, with the rest of the stars and celestial objects moving around it. Hence the name Hōkūpa‘a, meaning “Fixed Star” or “Stuck Star”.

Throughout February, the brightest star,  A‘ā (Burning Brightly), also known as Sirius or “the Dog Star”, will be visible in the early evening. This super bright star will be rising in Manu Malanai, the South East horizon, in the early evening. The second brightest star, Keali‘iokonaikaewa (The Chief of the Southern Heavens) also known as Canopus, will also be visible near Hema (South). These two bright stars form the handle of the starline Kekāomakali‘i (The Bailer of Makali‘i). Just as a bailer for a canoe scoops out water, this bailer scoops up the stars from Hikina(East) and pours them out into Komohana (West).

In particular the bailer is scooping up the bright shape of Kaheiheionākeiki (The Cats Cradle of the Children) also known as Orion. Beneath the famous three stars (known as the Orion’s Belt) that cut through the middle of Kaheiheionākeiki lies the gray fuzziness of M42, the Orion Nebula, arguably the most famous stellar nursery in the sky.

Setting in the western sky will be the “W” shape of  ‘Iwakeli‘i (Chief Frigate Bird), also known as Cassiopeia. Just beneath ‘Iwakei‘i will be the faint Andromeda galaxy. To the naked eye, the galaxy appears to be a small, faint, blurry smudge in the night sky. About 2.5 million light years away from Earth, Andromeda is the closest galaxy to the Milky Way.

 

Early Morning Observations:
Throughout February, sunrise occurs near 7 am, giving early risers a beautiful view of the sky. During these early morning hours the planets of Jupiter, Mars, and Saturn will line up in the south east, in front of the Milky Way bulge.

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