What is the longest day of the year in Hawaii?

Bishop Museum’s Jhamandas Watumull Planetarium opened its doors on December 12, 1961. Originally called the Kilolani Planetarium, the Watumull Planetarium has served over six million visitors and students over 60 years of continuous operation. The Planetarium was instrumental in the recovery of the nearly lost art and science of traditional, non-instrument navigation in Hawaiʻi. Nainoa Thompson spent countless hours in the Planetarium with Will Kyselka and other Planetarium staff in the late 1970s learning how to read the night sky. We are honored to continue that legacy by serving as a training space for today’s navigators.

Our GOTO Chronos II optical star projector provides one of the most vivid, realistic recreations of the night sky available today, with 8,500 pinpoint stars and realistic, bright planets. Our Digistar 4K
full-dome video system covers the entire dome in immersive video, allowing us to fly through the rings of Saturn, into the depths of the Orion nebula, out to the edge of the universe, and even simulate a voyage across the Pacific.

The Planetarium has 64 seats and serves 70,000 people a year. The planetarium focuses on programs about Hawaiʻi, blending live and prerecorded elements within each program.

Here is a comparison of the relative day lengths (number of hours of daylight) in different cities (of varying latitudes) on three dates in 1998.

You can see that on March 21, the spring equinox, all the cities listed have approximately 12 hours of sunlight. On June 21, the summer solstice and longest day of the year for the northern hemisphere, the day length ranges from about 13 ½ hours in Hawaii to 24 hours in northern Alaska. On December 21, the shortest day of the year, the day length ranges from almost 11 hours in Hawaii to 0 hours in Northern Alaska.

This diagram shows the earth’s position relative to the sun on the summer solstice in the northern hemisphere. The summer solstice is the longest day of the year (that is, the day with the most hours of daylight). When it is the summer solstice in the northern hemisphere, it is the winter solstice in the southern hemisphere—the shortest day of the year.

Remember that for the earth:

• one day equals one complete revolution on its axis.
• one year equals one complete orbit around the sun.

On the diagram you’ll see that the earth’s axis of rotation isn’t perpendicular to the sun. Rather, the earth’s axis is tipped at a 23.5 degree angle. This angle remains constant as the earth orbits the sun. When the northern hemisphere is tipped toward the sun, it is summer there. Six months later, when the earth’s orbit reaches the other side of the sun, the northern hemisphere will be tipped away from the sun, and it will be winter.

Find the equator on the diagram. Moving north, we’ve labeled the latitudes of Honolulu, Hawaii, Burlington, Vermont, and Barrow, Alaska. South of the equator, in the southern hemisphere, you’ll find Hamilton, Australia. Following are these cities’ latitudes, from northermost to southermost:

• Barrow, Alaska: 71 degrees North
• Burlington, Vermont: 44 degrees North
• Honolulu, Hawaii: 21 degrees North
• Equator: 0 degrees
• Hamilton, Australia: 38 degrees South

Note the shading on the "dark side of the earth"—the half of the planet that is not receiving sunlight.

Now let’s put all these factors together to show the difference in relative day lengths of each of these cities. The dark lines indicate the portion of the day that is in daylight. The dotted/dashed line indicates the portion that is in darkness.

Let’s start with Alaska. You can see from the diagram that at no time of the earth’s revolution is Alaska out of the daylight. On this day, the sun never sets—the "day length" is 24 hours!

Moving south, you can see that most of Vermont’s day is lit by sunlight; only a small percentage of the day, maybe one third, is in darkness. On the summer solstice, Vermont’s daylength is 15.5 hours.

In Hawaii, slightly more than half the revolution is in daylight, or 13.5 hours.

In Australia, less than half the revolution receives daylight, only 9 hours.

The purpose of all this is to show that day length, or number of hours of daylight, varies dramatically with latitude at certain times of the year. The further you get from the equator, the more dramatic the difference in the number of hours of daylight during the longest and shortest days of the year.

Now let’s look at another factor besides day length that influences the onset of flowering.

Note:  See the last page for a link to a web site with a chart showing the time of sunrise and sunset for cities across the U.S. for any year.

June will be the last month where we can clearly see Hanaiakamalama, the Southern Cross, in our early evening sky. Throughout early June, this notable shape will be directly over the direction of Hema — south on our star compass — in our early evening sky; however by the end of June it will begin to set into Manu Kona, the southwest horizon. It will reappear once again in the early morning sky in December.

Hanaiakamalama is the end of the star line, Kaiwikuamo‘o, the Backbone. Beginning with Nahiku, the Big Dipper in the northeast, the two pointer stars in its bucket point toward the direction of Hokupa‘a, Polaris, the north star.

If you follow a curving line from the handle of the Big Dipper southward, the next brilliant star in its path is Hokule‘a, Arcturus; then Hikianalia, Spica; then the trapezoid box Me‘e, Corvus; and finally the line terminates in Hanaiakamalama.

The Southern Cross is a significant constellation for oceanic explorers heading north toward Hawaii as it points toward the direction Hema, south on our sidereal star compass.

Compasses, sidereal or magnetic, all work on the same principle: By pinpointing one known location along the horizon, magnetic north on the magnetic compass or polaris on the sidereal compass, you can identify the 32 headings of the magnetic compass or the 32 houses of the oceanic sidereal compass.

The stars and our islands

At Kahikinui, Maui, along the southern coastline, winds from the ‘Alenuihaha Channel sweep the rugged shoreline constantly. In the shadow of Haleakala are two puu, or cinder cones, known as Pimoe, the name of the magical ulua that the demigod Maui fished for, and Hokukano, meaning proud star. To the southeast of these cinder cones lies the panana at Hanamauloa at Luala‘ilua. The panana is a pre-contact navigational structure or “sighting wall” designed to identify the point we call Hema.

The wall is approximately 29 feet long, 5 feet wide and 5 feet tall with a 2-foot notch at the center of the wall. Seaward of the wall sits an ahu, or stone cairn. Looking through the notch toward the cairn provides a relative line southward along the celestial meridian.

When Hanaiakamalama is upright, it stands directly above the notch and frames the direction to the southern horizon. The panana at Hanamauloa serves as navigational monument to voyagers from generations past.

Special events

June 21 marks the summer solstice, the day when the Northern Hemisphere is at its farthest tilt toward the sun and experiences its longest period of daylight of the year. The day length for Hono­lulu on the solstice will be 13 hours and 25 minutes.

Featured astronomical project

Using high-resolution adaptive optics imaging from the Gemini Observatory, astronomers have uncovered one of the oldest star clusters in the Milky Way galaxy, HP1. This star cluster is estimated to be about 12.8 billion years old, making these stars among the oldest ever found in our galaxy.

This ancient cluster is a part of the fundamental building blocks that assembled our galaxy’s central bulge. To learn more about this amazing study and how it unlocks the secrets of our own origins visit: gemini.edu/node/21165.

Evening observations

Throughout June, the bright planet Jupiter will be rising out of Manu Malanai, the southeast horizon, in the early evening. This gas giant planet is the fourth-brightest object we see in the sky, after the sun, moon and Venus. On June 10 Jupiter will be in a unique position known as opposition, when an outer planet (a planet farther from the sun than Earth) is lined up with the Earth and the sun. As Jupiter will be on the opposite side of the sun, from our perspective, it will rise at the same time as the sunset and will be in the sky the whole night. When Jupiter is at opposition it is at its closest physical position to us and will appear to be brighter in our sky.

In the early evenings of June 16-19 the planets Mercury and Mars will be going through a conjunction near Manu Ho‘olua, the northeast horizon. A conjunction is when two planets appear to be very close together (less than 1 degree away from each other) in the sky. The best time to see the two planets in conjunction on these days will be between sunset and 8:30 p.m.

Morning observations

As summer season approaches, the days will be longer and the sun will be rising earlier in the morning. Throughout June the sun will rise at or around 5:50 a.m., and dawn will start to color the sky just before 5 a.m. If you are up before sunrise keep an eye out for the incredibly bright planet Venus, which will rise just before the sun does in the eastern sky. At the same time the fainter planet Saturn will be high in the southwestern sky.

Skywatch, May 26 by on Scribd

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Chad Kalepa Baybayan () serves as navigator-­in-residence and Emily Peavy () as planetarium technician support facilitator at the ‘Imiloa Astronomy Center of ­Hawaii, a center for informal science education at the University of Hawaii at Hilo showcasing astronomy and Hawaiian culture as parallel journeys of human exploration.