On November 14, the moon will rise over the horizon showing a size slightly larger than usual: it will be a supermoon. If in itself, the rising of the Moon is a phenomenon that draws attention due to its beauty, in this occasion with more reason.
The apparent size change of the Sun and the Moon is a phenomenon that occurs when they rise and set over the horizon; It is due to an optical effect that occurs when comparing these stars with terrestrial objects (trees, houses …), so it is nothing more than an optical illusion.
However, the increase in size of the next full moon is due to another cause. On this occasion, the Moon will be 14% larger in apparent size and will shine up to 30% more than usual , since it will be at the closest distance to Earth in the last 70 years: 354,512 kilometers. This approach will coincide with the full Moon phase, so the phenomenon will be even more striking.
Why does this approach take place?
Kepler’s first law (year 1609) determined that the stars of the solar system move by tracing elliptical orbits. In the case of the Moon, if its orbit around the Earth were circular, the distance would always be the same, but when following an elliptical orbit, where the Earth is one of the foci, the distance varies from 356,400 kilometers (lunar perigee ) at 406,700 kilometers (lunar apogee) . These distances vary from one lunation to another.
The calculation of the distance between the Earth and the Moon was greatly improved thanks to the Apollo missions, which between 1969 and 1974 installed several retro-reflectors on the lunar surface. These devices returned the laser light beam that had been sent back to Earth. For 41 years scientists have been collecting data that have helped to calculate the distance between the two stars with an error of 3 centimeters. Thanks to this system we know that the Moon moves 3.8 centimeters away from the Earth each year, as well as the most precise calculation of its orbit.
Also, this lunar month, which is the period between two new moons, is going to be the longest of the year. If the average duration of a lunar month is 29 days, 12 hours and 44 minutes, this time it will last 29 days, 18 hours and 40 minutes, almost 6 hours more. This happens when two consecutive new moons coincide with the lunar apogee.
What implications does the supermoon have?
The phenomenon of the supermoon of this month can have an effect on the tides, due to the interaction of the forces of gravity, and also on the nocturnal species most sensitive to light; but there are no scientific studies that support other effects beyond those we discussed.
The best method to enjoy this phenomenon is with the naked eye, with the naked eye. No need to use binoculars or telescopes. The Moon will show a flat surface and features of the lunar relief cannot be observed, since sunlight falls directly on the moon. This is a good opportunity to practice night photography with the Moon as the protagonist or simply enjoy the phenomenon watching its rise over the horizon.
Amadeo Aznar, Isaac Aznar Observatory, CAAT-Alto Turia Astronomical Center.
