There’s a huge difference between the two episodes of the moon – “apogee“, wherein it is seen a bit farther as visible to the naked eye and a “perigee”, wherein it seems a lot bigger to us observers. Earlier this January, we observed the moon’s apogee phase. By the end of the month, many of us across the globe will yet again bear witness in anticipation of a grand lunar spectacle, a super moon, otherwise known as the blue moon. It refers to two (2) full moons in a single calendar month. This coincides with a total lunar eclipse in reference to the full moon lining up with the Earth and the Sun, according to the National Aeronautics and Space Administration (NASA).
Additionally, NASA stated that for a total lunar eclipse to happen, the moon must be full, which means it is directly opposite to the sun, with the Earth in between. The eclipse happens when the moon moves into the shadow cast by the sun shining on Earth. An eclipse does not happen every month because the moon is usually above or below the shadow (See Figure 1).
A perigee episode will make the moon appear 14 percent larger to the observer and 30 percent brighter and closer to the horizon. As for the blue moon, this is often misconstrued as infrequent lunar event. However, this is being debunked as a myth based on NASA data, because apparently it recurs every 2.5 years.
According to a Forbes report, a super blue blood moon, as termed by NASA was nicknamed for the reddish hue cast on the moon. The term blood moon refers to a total lunar eclipse where a full moon lines up with the Earth and Sun. In this configuration, the Earth blocks out the Suns’s light, turning the moon from a white glowing orb to a deep red orb (See Figures 2 and 3). There will be two (2) significant events happening on the 30th and 31st of January 2018. First, the perigee moon will be at closest to the Earth by 358,995 km. Second, the Earth-Sun distance is about 149,785,000 km while the moon is at 384,835 km apart from the surface of the Earth.
Affecting the tides
Some of us may wonder what are the direct effects of these moon phases to the Earth. Apparently, they have an effect on the oceans’ tides, all because of gravity (See Figure 4). This is confirmed by Sir Isaac Newton in 1687, wherein he explained that ocean tides result from the gravitational attraction of the sun and moon on the oceans of the Earth (Sumich, J.L., 1996).
To know how much the moon affects the tidal behavior of the Earth, let us look further into the mass involved with the Sun. It is 27,000,000 times larger than that of the moon, but it is 390 times farther away from the surface of the Earth. This means the moon has 46 percent reduction of the tide-generating force. This is twice the tide producing force versus the sun. This makes the moon the most dominant force affecting tidal action on our planet.
The moon has four (4) phases – the new moon, first quarter, full moon, and the last quarter. Also worthy to mention are the several factors affecting the tides on the Earth. These are drawn by accelerating or retarding influences of hydraulic, hydrodynamic, hydrographic, and topographic origin – and may further by modified by meteorological conditions such as wind and pressure.
By: Adonis S. Manzan