本文介绍了月球的周期性变化及其可见度的规律。月球的八种主要相位，从新月到满月再到下一个新月，构成一个约29.5天的完整周期。这些相位的形成是由于月球绕地球公转时，太阳光照射到月球不同部分的角度变化。文章以7月31日为例，说明了当天的月相为“盈凸月”，约41%的月面可见，并提供了肉眼、双筒望远镜和望远镜分别能观测到的月面特征，如月海和陨石坑。同时，文章还预告了下一次满月日期为8月9日，并详细解释了月相形成的科学原理，帮助读者更好地理解和观测月球。

🌕 月球的八种主要相位是周期性天文现象，由月球绕地球公转过程中太阳光照射角度变化引起，整个周期约为29.5天。这些相位包括新月、盈凸月、上弦月、盈凸月、满月、亏凸月、下弦月和亏眉月，它们展示了月球被太阳照亮部分在地球上可见的变化。

🔭 在7月31日，月相处于“盈凸月”，约41%的月面可见。通过肉眼可以观测到风暴洋、静海和丰饶海等月海区域；使用双筒望远镜则能看到恩迪米翁陨石坑、宁静海和波西多尼乌斯陨石坑等；而使用望远镜，则可以观测到更精细的地貌，如阿尔达德斯月溪、阿波罗16号着陆点和阿尔泰断崖。

🗓️ 文章预告了下一次满月将在8月9日出现，而上一次满月发生在7月10日。理解月相的周期性有助于预测和安排观测活动，例如，满月时月球的整个正面都会被太阳照亮，呈现最完整的圆形。

💡 月相的变化是理解月球与地球、太阳相对位置的关键。我们总是看到月球的同一面，但其可见的被照亮程度随在轨道上的位置而变化，这是造成从地球上看月球形状不断变化的原因，形成了我们熟悉的各种月相。

The moon is inching closer to being half lit, which means we're getting closer to a new moon phase.

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 tonight, July 31?

What is today’s moon phase?

As of Thursday, July 31, the moon phase is Waxing Crescent. There's 41% of the moon's surface visible to us on Earth (according to NASA's Daily Moon Observation).

It's day seven of the lunar cycle, and the last moon in July. As we say goodbye to another month, let's see what will be visible to us on the moon tonight.

With the unaided eye, enjoy a glimpse of the Mare Serenitatis, the Tranquillitatis, and the Mare Fecunditatis, an impact basin also known as the "Sea of Fertility."

With binoculars, you'll also get a glimpse of the Endymion Crater, the Mare Nectaris, and the Posidonius Crater, a lava-filled impact crater that's visible from the fifth to the 19th day of the lunar cycle.

If you have a telescope, position it in the middle right, descending (middle left, ascending if in the Southern Hemisphere) to see the Rima Arladaeus, the Apollo 16, and the Rupes Altai, a circular cliff around 298 miles long.

When is the next full moon?

The next full moon will be on August 9. The last full moon was on July 10.

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.