文章介绍了月球的周期性变化，即月相。月相是由于月球绕地球公转，太阳光照射角度不同而产生的视觉现象，整个周期约为29.5天。文章详细阐述了新月、蛾眉月、上弦月、盈凸月、满月、亏凸月、下弦月、残月这八种主要的月相，并解释了其成因。此外，文章还提供了特定日期（8月15日）的月相信息（亏凸月，58%可见），并指导读者利用肉眼、双筒望远镜和望远镜观测月球表面的具体地貌，如月海和陨石坑，并预告了下一次满月的时间（9月7日）。

🌕 月相是月球绕地球公转过程中，受太阳光照射角度变化而呈现的不同外观，构成一个约29.5天的完整周期。这使得我们在地球上看到的月亮亮度及可见部分发生规律性变化。

🌟 文章详细列出了月相的八个主要阶段：新月（不可见）、蛾眉月（右侧出现细小光边）、上弦月（右侧半月）、盈凸月（右侧大于半月）、满月（整个月面可见）、亏凸月（左侧开始变暗）、下弦月（左侧半月）以及残月（左侧出现细小光边），直至再次进入新月。

🔭 文中以8月15日为例，指出当日月相为亏凸月，可见度为58%，并提供了观测月球表面细节的建议：肉眼可观测到风暴洋、哥白尼环形山等，使用双筒望远镜可观测加森迪环形山等，而使用望远镜则能看到阿波罗12号着陆点、阿尔卑斯山脉等更精细的地貌。

📅 文章还提供了重要的时间节点信息，预告了下一次满月将在9月7日出现，而最近一次满月则发生在8月9日，为天文爱好者提供了宝贵的观测参考。

The moon goes through a repeating cycle of phases each month, changing what we see every night. This is called the lunar cycle.

The lunar cycle is a series of eight unique phases of the moon's visibility. The whole cycle takes about 29.5 days, according to NASA, and these different phases happen as the Sun lights up different parts of the moon whilst it orbits Earth. 

So, what's happening with the moon tonight, Aug. 15?

What is today’s moon phase?

As of Friday, Aug. 15, the moon phase is Waning Gibbous, and it is 58% lit up to us on Earth, according to NASA's Daily Moon Observation.

Alongside this, with no visual aids on the moon, you can spot the Mare Imbrium, Copernicus Crater, and the Oceanus Procellarum, an "Ocean of Storms" that covers more than 10% of the moon's surface.

With binoculars, enjoy glimpses of the Gassendi Crater, Alphonsus Crater, and the Alps Mountains. If you have a telescope, the Apollo 12, Caucasus Mountains, and the Schiller Crater will all be in view too.

When is the next full moon?

The next full moon will be on Sept. 7. The last full moon was on Aug. 9.

What are moon phases?

According to NASA, moon phases are caused by the 29.5-day cycle of the moon’s orbit, which changes the angles between the Sun, Moon, and Earth. Moon phases are how the moon looks from Earth as it goes around us. We always see the same side of the moon, but how much of it is lit up by the Sun changes depending on where it is in its orbit. This is how we get full moons, half moons, and moons that appear completely invisible. There are eight main moon phases, and they follow a repeating cycle:

New Moon - The moon is between Earth and the sun, so the side we see is dark (in other words, it's invisible to the eye).

Waxing Crescent - A small sliver of light appears on the right side (Northern Hemisphere).

First Quarter - Half of the moon is lit on the right side. It looks like a half-moon.

Waxing Gibbous - More than half is lit up, but it’s not quite full yet.

Full Moon - The whole face of the moon is illuminated and fully visible.

Waning Gibbous - The moon starts losing light on the right side.

Last Quarter (or Third Quarter) - Another half-moon, but now the left side is lit.

Waning Crescent - A thin sliver of light remains on the left side before going dark again.