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ʻApelila (April) Sky Watch

by Imiloa Astronomy Center on March 27th, 2018

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

Spring Starline in the Hawaiian Star Compass

 

On March 20, the sun crossed north over the equator in an event called the Equinox, a juncture when daylight and nighttime are approximately equal in length, heralding the beginning of spring in the Northern Hemisphere. The Hawaiian word associated with this season is Kupulau (Sprouting Leaf). Today’s column returns to learning the night sky through the eyes of oceanic voyagers by examining the second Hawaiian starline, Kaiwikuamoʻo, which stands out during spring and early summer.


As mentioned in past columns, starlines are collections of bright stars and constellations that line the night sky in a north-south direction. In the Hawaiian star chart, the four starlines are, Kekāomakaliʻi (The Bailer of Makaliʻi), Kaiwikuamoʻo (The Backbone), Mānaiakalani (The Heavenly Fishing Line) and Kalupeakawelo (The Kite of Kawelo). Because each is most prominent in the night sky during a different time of the year, they also serve as seasonal markers for winter, spring, summer, and fall.

 

In January’s column, we introduced the first starline, Kekāomakaliʻi, which is prominent during the winter season. The third starline, Manaiakalani, will be presented this summer and the fourth starline, Kalupeakawelo, will be featured this fall.


The easiest constellation to identify in the Kaiwikuamoʻo starline, is Nāhiku,“The Big Dipper,” rising in the direction Manu Koʻolau, northeast on our star compass. The seven stars of Nāhiku form the shape of a celestial ladle. Drawing an imaginary line from the two pointer stars in the scoop of the dipper to the horizon will lead you toward Hōkūpaʻa (Polaris), also known as “The North Star.” Hōkūpaʻa is positioned very near the north celestial pole so it seems to be motionless while other stars appear to rotate around it. Hōkūpaʻa is part of the constellation “The Little Dipper” which resembles a second smaller celestial ladle. These two buckets (Little and Big Dipper) are said to be pouring into each other.

If you follow the handle of Nāhiku eastward you arrive at the fourth brightest star in the night sky, Hōkūleʻa (Arcturus). Hōkūleʻa rises in the star compass direction ʻĀina Koʻolau (east-northeast), passing directly over Hawaiʻi Island, and is the zenith star (star at the highest point on the celestial sphere) for the Hawaiian Islands. Following Hōkūleʻa in the direction of Lā Malanai (southeast) on our star compass, brings you to Hikianalia (Spica), in the constellation Virgo. Hikianalia is actually comprised of two stars rather than one, a blue giant and a variable star, because the two stars orbit each other and are too close together to separate visually.


Continuing in a southward direction around the star compass, you will see a celestial quadrilateral shape, a box with a short and a wide end, known as Meʻe (Voice of Joy) to oceanic voyagers and Corvus (Latin for crow or raven) to astronomers. Taking a line through the center of Meʻe toward the southern horizon will lead you to a constellation held in special regard by Pacific navigators: Hānaiakamālama (Cared for by the Moon) also known as the Southern Cross, which rises around 9pm in April.


Navigators can use Hānaiakamālama to determine the direction of Hema, south on our star compass. This constellation is also important for establishing the latitude of the Hawaiian Islands. When Hānaiakamālama is in the upright position, at around 11 pm during April, you can measure the distance between its top star and bottom star and when you can establish the same distance equally between the bottom star and the horizon beneath it, you know you are at the latitude of Kahoʻolawe. At that point, simply turn your canoe downwind, and the wind will sail your canoe towards the Hawaiian Islands.

Special morning observations: 

Between 3am and 6am towards the south-eastern sky of April 2, Mars and Saturn will be going through a conjunction. A conjunction is when celestial objects appear to be very close together (within a few degrees) in our sky. A planet will frequently conjunct with celestial objects as well as other planets. The red dot of Mars will appear to be very close to the faint yellow dot of Saturn.

 

Every year in April, when Earth passes through Comet Thatcher’s dusty tail, a meteor shower, known as the April Lyrids, occurs. This shower is the oldest known shower ever recorded, as it was chronicled in the Zuo zhuan (ancient Chinese narrative history) in 678 B.C. Observers can enjoy watching this year’s Lyrid meteor shower from April 16 to April 25, but the best time to see the meteors will be just before sunrise on April 22. At its peak, you can expect to observe about 20 shooting stars per hour, or approximately 3 meteors a minute.

 

At 4:44am on the morning of April 29, Mercury will be rising and will be visible until the light of dawn obscures it.  On this day, Mercury will be at a unique position in its orbit, known as the Greatest Western Elongation, and is at its furthest position from the Sun in the Eastern sky.

 

April’s morning sky

Throughout April, sunrise occurs between 6 and 6:30 am. During these early morning hours the planets of Jupiter, Saturn, and Mars will be high in the southern region of the sky. Sitting between the planets will be the beautiful bulge of the Milky Way Galaxy.

 

April’s night sky

During the early evening hours, the incredibly bright planet Venus will chase the sun into the horizon. Venus is the 3rd brightest object in the sky after the Sun and the Full Moon. As it is usually seen either just after sunset or immediately before sun rise, Venus is variously referred to as the “evening star” or the “morning star.”

 

The recognizable shape of Kaheiheionākeiki (The Cat’s Cradle), also known as Orion the Hunter, will be preparing to set into the west. On a nice dark night, you will be able to see the blur of the Orion Nebula beneath the famous three stars that cut across Orion’s Belt. The Orion Nebula (M42) is the most famous stellar nursery in the sky.

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