Discover why the MOON shines

The Moon it's the only one natural satellite of the planet Earth. A satellite is a celestial body that revolves around a planet. It has no light of its own. The only stars with their own light are the stars. Then,why the moon shines? In this lesson from a TEACHER we explain why the Moon shines, why it only shines at night and why, in the different lunar phases, the moon shines in its entirety, only in a part of its visible face or it does not shine in absolute.

Index

1. Why the moon shines: albedo, the ability to reflect light
2. Why the moon only shines at night
3. Why the moon shines with different intensity

As we have already commented, the Moon is a satelite Y does not emit its own light. Its brightness is due to its ability to reflect sunlight. The ability to reflect light is a physical property which receives the name of albedo.

This value oscillates between the values ​​of 0 (when all the light that falls on a celestial body is absorbed) and 1 (when all of the light that falls on is reflected). The Moon has an average albedo of 0.12, that is,

The reason for this ability to reflect light is given by the lunar surface color, which is grayish. It has been observed that the albedo of the lunar surface is not uniform but varies along its surface. The most recent formation soil of the lunar craters it has a higher albedo than the older formation soils.

The brightness of the Moon and the lunar phases

However, the albedo of the Moon is not constant and it depends on several factors. The main factor determining lunar albedo is the moon phase, because in the different phases of the Moon, sunlight shines at a different angle.

When the angle between the Sun, the Earth and the Moon increases, the albedo of the Moon decreases. The decrease in lunar albedo during certain phases is due to the shadows that lunar craters and mountains cast on their surface, reducing the amount of reflected light.

The maximum albedo of the Moon is reached when the angle of the Moon is 180º with respect to the Sun during the full Moon phase, that is, the Moon, the Earth and the Sun are aligned.

As we have already seen, the Moon shines because it is able to reflect part of the sunlight that falls on it. However, the brightness of the Moon, like the brightness of other celestial bodies, is only visible at night. This is due to the Earth has an albedo much higher than that of the Moon. Seen from the Moon, our planet is 100 times brighter than the Moon, due to its larger size and much higher albedo.

The average albedo of the Earth is 0.38, which means that reflects 38% of the light it receives from the Sun, while the Moon only reflects 7-8% of the light that falls on it. Some land surfaces reflect a much higher than average percentage of light, such as snow-covered areas that reflect 90% of the light or aquatic surfaces that reflect between 40 and 60% of the light that falls on they. Therefore, during the day, the light that our own planet reflects prevents us from seeing the brightness of the Moon.

However, sometimes the moon is visible during the day, because its brightness is especially intense and the light reflected by the Earth does not completely hide it. This happens in full moon phases in which it reaches its maximum brightness.

According the earth spins around the sun, Different areas of the Moon are illuminated by the Sun, and different lunar phases are observed from the Earth.

• In the phase of full moon the hemisphere of the Moon facing planet Earth is fully illuminated. The angle of incidence of sunlight changes as it moves around the Earth, as a function of this angle the albedo of the Moon changes, therefore changing the intensity with which shines.
• During the phase of New Moon It is the hidden side of the Moon that is fully illuminated, while the visible side remains dark; because the Moon is located between the planet Earth and the Sun. AND
• n the intermediate phases the moon only partially intervenes between the planet and the Sun so that the shaded area is only partial.

The intensity of the Moon's brightness varies depending on the Moon phases, shining 90% more when it is in the phase of the full Moon than when it is in the phase of the first quarter.

Another factor that influences the intensity with which the Moon shines is the distance to that of the Earth, the closer it is, the greater the intensity of its brightness.

The phenomenon of the supermoon

The supermoon is a phenomenon that occurs when the lunar perigee (point of the lunar orbit closest to the earth) with the full moon phase. At this time the Moon is perceived from the Earth 10-15% larger and its brightness is 30% greater.

If you want to read more articles similar to Why the moon shines, we recommend that you enter our category of Astronomy.

• Fatoumata Kébé (2020) The Book of the Moon. History, myths and legends. Barcelona: Blackie Books
• Luis Butten. (2013Why is the moon shining? The moon shines because it reflects the sunlight. But it's a pretty bad mirror, as other surfaces reflect even more light. Biorigen.com