Tides commonly occur during a full moon and the two natural phenomenon are known to be closely linked to each other.
By
BRIGITTA ISWORO LAKSMI
·4 minutes read
Kompas/Totok Wijayanto
Ismail, who works at the Old City management unit, tests a telescope on Tuesday (30/1) at Fatahilah Square in Central Jakarta. The square was open to the public for mass viewing of Tuesday’s supermoon.
The Meteorology, Climatology and Geophysics Agency (BMKG) warned residents of the possibility of high tides on Wednesday (31/1/2018). Tides commonly occur during a full moon and the two natural phenomenon are known to be closely linked to each other. It is estimated that there will be higher tides tonight.
This evening, the moon will on its perigee (the point in its orbit closest to Earth) making it appear larger than usual (a phenomenon known as super moon). In regions with four seasons, this total lunar eclipse will occur on the third of four full moons in one season. Usually, there are only three full moons in one season.
This third full moon used to be called the “betrayer”. The word “blue” in the idiom “blue moon” is believed to have derived from an Old English word “belewe” that means “to betray”. This is because a “blue moon” betrays the normal occurrence of three full moons in one season (Kompas, 30/1). The closer distance between the Moon and the Earth this time is believed to be an important factor in triggering high tides.
Similar with the Earth and its gravity, the Moon also has its own gravity. The moon’s gravity pulls everything to the center of the Moon. High tides occur due to the Moon’s gravitational pull.
The Moon’s gravity pulls seawater toward it. Why, then, are humans and other creatures not pulled toward the Moon as well? According to National Institute of Aeronautics and Space (LAPAN) Space Science Center researcher Agustinus Gunawan Admiranto, seawater is liquid and therefore easier to change shape. On humans, the Earth’s gravitational pull is far stronger than the Moon’s.
The Moon’s gravitational pull works on extended objects. Therefore, the surface of water in areas perpendicular to the Earth-Moon axis will be pulled, resulting in an ebb. The Earth’s gravitational pull is still far stronger than the Moon’s and seawater remains on Earth. “If the Moon’s gravitational pull is stronger, Earth’s water would have been ‘pulled away’,” Agustinus said.
Tides are also influenced by Earth’s moment of inertia. There is a centrifugal force (pulling outwards) making seawater moves outward from the Earth. Gravity and inertia pushes water on the outward direction from the Earth’s surface, therefore triggering tides.
Differences in gravity
During a full moon, the Sun is on a straight line with the Earth and the Moon and the Sun’s gravitational pull is bigger than the Moon’s. However, tides are more about the differences of gravitational pull on opposing sides of the Earth (on the location directly under the moon and its antipode).
The Earth’s radius is only 0.005 percent of the distance between the Earth and the Sun. Therefore, the difference of gravitational pull of the two surfaces is very small. On the other hand, the Earth’s radius is 1.7 percent of the distance between the Earth and the Moon. Therefore, despite the Moon’s gravitational pull being smaller than the Sun’s, it has a far stronger influence on tides.
Tides will move from locations to locations on Earth in line with the Moon’s movement circling the Earth. Therefore, in 24 hours and 50 minutes, one location will endure two tides and two ebbs.
The phenomenon of full moon is closely linked to a variety of myths. These include connecting full moons to menstruation cycles, sleep disruptions, aggressiveness in animals and even relapse in mental illnesses.
There is also the term “lunatic mind” in relation to mental illnesses. Almost all of these myths have been torn down by scientific researches. Most certainly, before electricity was discovered, the luminosity of a full moon might have disrupted people’s sleep cycle, leading to emotional disturbances.
