Supermoon: What Is It and How Does It Happen?

   A supermoon rising near the Lincoln Memorial in Washington. Credit: NASA/Bill Ingalls

What is Supermoon?

A supermoon is a full moon that occurs when the Moon or Luna is at its perigee or closest point to Earth. So what makes a super bear so special? There is much to see and learn for interested observers. 

• The Moon orbits Earth in an ellipse, which causes it to approach or move away from Earth as it orbits Earth.  
• The farthest point in the Moon's orbit around Earth is called the apogee, and it is about 253,000 miles (405,500 kilometers) away. 
• Its closest point is the perigee, about 226,000 miles (363,300 km) from Earth. 
• When the full moon appears in Periphery, it is slightly brighter and larger than a regular full moon - we have a "supermoon" here. 

In-Depth 

The term "supermoon" was coined in 1979 to describe a full moon that is slightly larger and brighter than usual because it occurs at or near perigee, the Moon's closest point to Earth. 

Point it to the nearest earth's orbit.   This word is essentially the geometrical arrangement of Moon-Sun-Earth-Moon, allowing perigee to occur over a larger period (up to two weeks, almost half of the moon's orbit) than the actual perigee. 

For those who watch closely, there are a few points that should be noted. Here is a photo of Luna from November 2016:

Both of these images show the Moon on the night of November 13-14, 2016, when it was at its closest point to Earth. The Moon appears larger near the horizon because of an optical illusion called atmospheric refraction. The right image shows the Moon at its highest point in the sky, where it appears slightly smaller.

The image on the left was taken after the moon rose at around 6 pm. local time when clearing mountain scenery. The photo on the right was taken at around 12:30 that night, as the luna was approaching its maximum. The line between the two graphs shows one small difference: The moon is getting smaller as it gets farther away. At that time, the moon's center is approximately the distance from the center of the earth and the observer. The Earth had turned a quarter turn when the second photo was taken, and the Moon was at its highest point in the sky. At the time, it was about 4,000 miles closer to the observer because the Earth's rotation placed the observer directly under the Moon; The center of the Earth is now further from the Moon than the observer. Except that the distance between the centers of these 6 planets is slightly different due to the orbital motion of the moon. After 6.5 hours, the distance between the observer and the moon gradually decreases, as can be seen from these two images. 

So what makes the supermoon different?  

Some periphery places are closer than others. The Moon's orbit is not a perfect circle but is more like an oval. This is because the gravitational forces of the Sun and other planets cause the Moon's orbit to change shape over time. 

Extreme perigee and apogee or furthest points in orbit occur in a forecast. Strange things: The supermoon is also in perigee.  The Extreme Perigee Full Moon will have a smaller radius and diameter than other full moons. Let's go back to November 13-14, 2016, the radius and diameter of the perigee full moon:  

• Less than 2% larger than an average perigean full moon. 

• Is less than 8 percent larger than the full moon would appear at the center of the Earth.  

• Is less than 14% larger than the average culmination of the full moon. By comparison, when you hold your little finger ("pink finger") on your arm, the width of your fingers is the same as the diameter of the full moon in the sky. 

Can you measure the difference with the naked eye?

November 2016 perigee full moon clouds cover a large area of the sky as seen from Earth: 

• less than 4% compared to the average perigee full moon. 
• Is about 14% smaller than Earth's apparent diameter. 
• Is less than 23% larger than the average culmination of the full moon. 

Set the sun's brightness to 1.00000 during the perigee of the full moon in November 2016, the moon's brightness: 

• The average perigee for the whole month is 0.99996. 
• The average distance of full moons is 0.99981. 
• The average value of the full moon in Apogee is 0.99967. 

This difference is due to the small difference in the moon's distance from the sun. In our eyes, the difference is indistinguishable. 

The cloudy perigee supermoon of November 2016 illuminated the earth's surface higher because the Moon is closer than usual to the sun and appears slightly larger than usual in the sky compared to other moons. If a cloudy perigee full moon gives a luminosity of 1.00000 on Earth's surface, then...

• The average perigean full moon is 0.99991. 
• The average distance of full moons is 0.99963. 
• The average value of the full moon in Apogee is 0.99934.  

Look around when the moon is full in the sky and there is no other light around, the difference between the light on the ground and our naked eye is different.

High and low tides tend to be even heavier at full moon and supermoon. The maximum value is larger due to the difference in the gravitational force of the Luna across the Earth's diameter. When the Moon is close, the Earth's diameter makes up a small fraction of the distance between the Earth and the Moon. The gravitational force of the Luna is strongest at the point on Earth closest to the Moon's center, and weakest at the opposite point on the Earth's axis. This difference in gravitational force causes the oceans to bulge out on the side of the Earth closest to Luna, and to bulge inward on the opposite side. This disrupts water flow. If perigee weather during November 2016 produces a tidal force value of 1,000,000, the resulting tidal force value is.   

• The average perigee for the entire month is 0.946493. 
• The average of the month is 0.797740.  
• The average distance of the Moon from Earth at apogee is 0.678594 astronomical units.

High tides during the full moon and new moon in Periphery can cause serious problems on some coasts, especially if the weather causes high tides or storm surges (due to air pressure below the nodal point).