Why Does the Moon Shine When Its Dark?

By Javier Sánchez, Biologist. July 20, 2023
Why Does the Moon Shine When Its Dark?

The moon has held a significant place in the hearts and minds of people throughout history. As the brightest object in our night sky, it has guided travelers and sailors for ages. Its changing phases have been celebrated across cultures, inspiring myths and legends of lunar deities and transformation. But, have you ever wondered why the moon shines so brightly in the night sky, even during darkness?

In this article, we explain the reasons behind the moon's luminous glow despite the absence of its own light source.

Why does the moon shine?

The moon's brilliance in the night sky has always captivated and puzzled us. But have you ever wondered why it shines so bright? The reason lies in how it interacts with the sun and Earth.

Unlike the sun, which is a massive ball of fiery gas and has its own light, the moon doesn't have any light of its own. Instead, it acts like a giant mirror, reflecting the sunlight it receives from the sun.

Surprisingly, the moon reflects only a small amount of the sun's light, somewhere between 3% and 12%. Scientists call this measurement "albedo," which tells us how much light a surface reflects compared to the total light falling on it. For example, a snowy mountain reflects about 95% of the sunlight it gets, making it look bright white during the day.

The moon, however, has a much lower albedo, around 7%, which means it reflects only about 7% of the sunlight it receives. You might wonder why the moon appears so bright despite reflecting so little light. Well, that's because it's relatively close to Earth.

The moon's closeness to us makes it look much brighter than it would if it were farther away. Its proximity, combined with its reflective surface, creates a captivating sight for us to enjoy.

During the night, when we see the moon shining brightly, it's not only because of the direct sunlight. Some of the sunlight that hits Earth during the day bounces back into space and reaches the moon. It's as if Earth is sharing its own shine with the moon, giving it that beautiful silvery glow.

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Why Does the Moon Shine When Its Dark? - Why does the moon shine?

How does the moon's composition enhance its brightness?

The moon's surface is a captivating mix of dark gray hues, shaped by a variety of minerals derived from the breakdown of basaltic rocks, anorthosites, and lunar dust. Let's take a closer look at how this unique lunar composition contributes to the moon's brightness and the fascinating dance of light on its surface.

The lunar surface is composed of different types of rocks, such as basaltic rocks and anorthosites. Basaltic rocks are formed from volcanic activity, and anorthosites are igneous rocks rich in a mineral called plagioclase feldspar. Over time, these rocks undergo disintegration and weathering processes, resulting in the formation of new minerals that contribute to the moon's overall appearance.

However, it's the lunar dust that adds a remarkable touch to the moon's surface. This fine dust is a result of continuous bombardment by hydrogen from the solar wind and the presence of metallic iron on the moon. The combination of these factors creates a delicate layer of dust that settles on the lunar surface.

When sunlight, X-rays, and ultraviolet radiation reach the lunar surface, they interact with the materials present there. These interactions alter the electrons' state within the materials, causing the lunar surface to gain a positive charge. As a consequence of this phenomenon, tiny particles of lunar dust are released into space.

The released lunar dust doesn't just disappear; it forms a delicate orbital dance around the moon. These particles move in orbits that can range from a few meters to several kilometers. This orbital movement of lunar dust is what ultimately contributes to the mesmerizing effect of greater light reflection.

The interplay of light and charged lunar dust creates a spectacle of brightness, making the moon appear even brighter than the amount of light it directly reflects from the sun.

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How does the moon's orbit and phase influence the brightness of the moon?

The brilliance of the moon that we observe from Earth is intricately tied to its position and phase during its orbit around our planet. As the moon gracefully completes its orbit around Earth in approximately 29 and a half days, different angles of sunlight illuminate its surface, creating the mesmerizing array of moon phases that we are familiar with.

From our vantage point on Earth, we can only see the half of the moon that is directly illuminated by the sun. This phenomenon occurs because, like a cosmic dance, the moon orbits around Earth, and Earth, in turn, orbits around the sun. This delicate interplay between the moon's orbit around Earth and Earth's orbit around the sun leads to the various phases of the moon:

  • New moon: during this phase, the moon is situated between the sun and Earth. As a result, the side of the moon that reflects sunlight is facing away from us, making it not visible from Earth.

  • Crescent moon: as the moon continues its orbit, a slender crescent of light becomes visible on the side that is gradually turning towards the sun.

  • First quarter moon: at this point in the orbit, half of the moon's surface is bathed in sunlight, while the other half remains in the shadows.

  • Waxing gibbous moon: during this phase, the illuminated portion of the moon grows, becoming more prominent and making it appear larger to us.

  • Full moon: the brightest and most captivating moment in the moon's trajectory occurs when it is about 180 degrees from our perspective. At this point, the entire half of the moon facing Earth is fully illuminated by the sun, creating the mesmerizing phenomenon of the full moon.

  • Waning gibbous moon: after the full moon, the illuminated portion begins to decrease, gradually transitioning from a full moon to a waning gibbous moon.

  • Last quarter moon: half of the moon's surface is still visible, but now the illuminated portion is decreasing.

  • Waning moon: as the moon's orbit continues, the illuminated portion further decreases until it transforms into a slender crescent, marking the return to the crescent moon phase.

  • Black moon: in rare cases, when there are two new moons in a calendar month, the second new moon is referred to as the Black Moon.

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Why Does the Moon Shine When Its Dark? - How does the moon's orbit and phase influence the brightness of the moon?

What shines brighter, the sun or the moon?

The sun shines much brighter than the moon because it has its own powerful light source, while the moon relies on reflecting sunlight to illuminate the night sky.

This distinction is crucial in understanding why the sun appears so dazzling, and looking at it directly can be harmful to our eyes. On the other hand, gazing at the moon for longer periods is safe, since it merely reflects the sunlight it receives and doesn't emit its own intense light.

The sun, being a star, is an incredibly energetic and luminous celestial body. Its intense brightness is due to the nuclear fusion reactions taking place deep within its core, releasing vast amounts of energy and emitting light in all directions. This powerful light reaches Earth and bathes it in warmth and illumination during the day.

In contrast, the moon lacks an internal light source, and its surface acts like a mirror, reflecting the sun's light back towards us. This reflection is what makes the moon visible and bright in our night sky. While the moon's reflective surface can appear quite radiant, it pales in comparison to the overwhelming brilliance of the sun.

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If you want to read similar articles to Why Does the Moon Shine When Its Dark?, we recommend you visit our Facts about Earth and the universe category.

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