Skywatch: Geminid meteor shower to dazzle December skies
The annual Geminid meteor shower runs through the first two weeks of December and peaks around 2 a.m. Dec. 14.
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The four stars that form the corners of Ka Lupe a Kawelo, or the Great Square of Pegasus, are excellent pointer stars that point to the north and south celestial poles and indicate the path it takes across the night sky as it moves from the eastern to the western horizon.
The first two stars that appear in the east are Kakuhihewa, or Scheat, which rises on the boundary of the compass house Noio-‘Aina Ko‘olau, and Keawe, or Markab, which rises on the boundary of Aina-La Ko‘olau. Because they rise at about the same time, they will cross the celestial meridian together. A pair of stars that cross the meridian together is called a meridian pointer.
In the tropics, meridian pointers are excellent pointer stars to the celestial north and south poles. The second pair of stars in Ka Lupe a Kawelo to arrive in the east are Manokalanipo, or Alpheratz, and Pi‘ilani, or Algenib. They rise and set along the same boundaries of Noio-‘Aina Ko‘olau and ‘Aina-La Ko‘olau. These two sets of stars point toward the north celestial pole.
To find the south celestial pole, draw a line through Kakuhihewa and Keawe; continue the line southward and through Kukaniloko (Fomalhaut) for one set of southern meridian pointers. For the second set of pointers, draw a line through Manokalanipo and Pi‘ilani and through Kaikilani (Ankaa). By using the four stars of Ka Lupe a Kawelo in this way, you can identify the north and south celestial poles.
Because Kakuhihewa, Manokalanipo, Keawe and Pi‘ilani rise and set in the same compass house, they will always point out the direction to those compass houses on the horizon. Within the tropics you can draw a line between these stars and calculate the angular path these stars take on their nightly east-to-west trek.
The annual Geminid meteor shower runs through the first two weeks of December and peaks around 2 a.m. Dec. 14. Considered by many to be the best meteor shower of the year, it features multiple shooting stars a minute during its peak. The Geminid shower is peculiar because its meteors do not originate from a comet, but from the asteroid 3200 Phaethon, whose orbit passes close to Earth’s orbit every 1.433 years.
Winter solstice for the Northern Hemisphere is Dec. 21. The sun will travel at its lowest arc across the sky, marking the shortest day and longest night of the year. On Dec. 21, in Honolulu, the sun will rise at 7:04 a.m. and set at 5:54 p.m., yielding only 10 hours and 50 minutes of daylight.
Amid the stars of Ka Lupe a Kawelo will be the distinctive red planet, Mars, which always stands out in the evening sky due to its signature color. This red comes from the iron oxide that is present in the regolith of the planet. Mars observers will be able to note its changing position in the sky.
In July, Mars was seen in the early evening sky as it was in the western constellation of Capricorn, close to Pimoe in Manaiakalani. By December, Mars will be in front of the western constellation of Aquarius, among the lines of Ka Lupe a Kawelo. Mars will remain in our sky into 2019 and will shift position against the background of stars night after night.
While looking toward the body of Ka Lupe a Kawelo, about 10 degrees north and west of the star Manokalanipo, and almost 20 degrees south of ‘Iwakeli‘i, you can see a small faint smudge in the sky. This faint object is the Andromeda Galaxy, the closest full-size galaxy to the Milky Way and the only object you can see with your naked eye that is outside of our own galaxy.
Rising from the east is the distinctive star cluster of Makali‘i, also known as the Pleiades. This stellar open cluster stands out with its seven brightest stars being 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.
In December the sun will rise around 7 a.m. with dawn beginning to brighten the sky starting at 6 a.m. As the days get shorter, there will be more observation opportunities during the early morning hours.
At 6 a.m. Venus and Jupiter can be seen rising in the east while the bright star, ‘A‘a, also known as Sirius or the dog star, will be setting in the west. After the sun and the full moon, these three objects are the third-, fourth- and fifth-brightest objects you’d ever see in the sky.
Dec. 15 marks Mercury’s greatest western elongation, when Mercury will be at its highest position from the eastern horizon. This will be the best morning to observe Mercury in the sky. Farther south in the sky will be the return of the Southern Cross to Hawaii’s skies.
December 2018 Sky Chart by Honolulu Star-Advertiser on Scribd
Chad Kalepa Baybayan (Kalepa.Baybayan@hawaii.edu) serves as navigator-in- residence and Emily Peavy (Emily.Peavy@hawaii.edu) as planetarium technician support facilitator at the ‘Imiloa Astronomy Center of Hawai‘i, a center for informal science education at the University of Hawaii at Hilo showcasing astronomy and Hawaiian culture as parallel journeys of human exploration.