The biggest and brightest full moon of the year arrives tomorrow as our largest natural or otherwise satellite comes a little closer than normal. It will, at least from our perspective on Earth appear a bit bigger – a good experiment – take a photo tonight and take one next full moon in the same place and see if it is true.
The term ‘Supermoon’ is a nickname for a perigee full moon, this is the when the Moon is closer to the Earth than usual in its orbit. Apogee and perigee refer to the distance from the Earth to the moon. Apogee is the furthest point from the earth while Perigee is the closest point to the earth and it is in this stage that the moon appears larger. Looking at the moon in the sky without anything to compare it to, you wouldn’t notice any size difference. But the difference in size can in fact be quite significant.
If you were to take a picture when the Moon is at perigee and again at apogee using the same camera and lens you would notice the difference.
The full Moon occurs at 1:35pm (AEST) Sunday May 6th in Australia. It is predicted that the moon will about 14 per cent brighter than usual.
Sunday’s event is a “supermoon,” the closest and the biggest and brightest full moon of the year. At 1.35 p.m., the moon will be about 356,956 km from Earth. That’s about 24,653 km closer than it is on average.
That proximity will make the moon appear about 14 percent bigger than it would if the moon were at its farthest distance, however, the difference in appearance is so small that you will find it hard pick it with your unaided eye.
The moon’s distance from Earth varies because it follows an elliptical orbit not a circular one.
Like any full moon, tomorrow’s moon will look bigger when it’s on or near the horizon rather than higher in the sky, thanks to an optical illusion. The full moon appears on the horizon at sunset. On the East coast, for example, that will be a at 5.07pm.
The last “supermoon” on March 20, last year was about 380 km closer than this year’s will be. Next year’s will be even a bit farther away than this year’s. Each year there is a perigee and an apogee Moon and the distances vary.
One effect that can be noticed doesn’t affect me where I live, but coastal folks are very familiar with the tides and how their height varies over the course of a month, again, due to the Moon not always being the same distance from the Earth. As the Moon’s orbit brings it in closer proximity to our planet, its gravitational forces can increase by almost 50%, and this stronger force leads to high tides. Likewise, when the Moon is farther away from the Earth the tides are far less spectacular.
The Moon’s influence can also be balanced out by the position of the Sun – if the Sun and the Moon find themselves 90 degrees apart in relation to an observer on the Earth, then high tides are not as high as they normally would be. This is because despite its greater distance from the planet, the Sun’s mass allows it to exert enough gravitational force on the oceans that it can negate some of the effects of the Moon’s pull. This phenomenon of lower high tides is called a neap tide. In the same way, when the Sun lines up with the Moon and the Earth, as during a Full Moon, then the Sun can act to amplify the tidal forces, drawing even higher tides. These are known as spring tides, named not for the season, but for the fact that the water “springs” higher than normal. The variance in the height of the world’s tides also depends on the local geography of the coastline and the topography of the ocean floor.