文章介绍了月相变化的科学原理，即月球绕地球公转导致太阳光照射角度不同，从而呈现出不同可见部分。我们看到的月相是月球在29.5天周期内，受太阳光照射而产生的八种不同形态。当前（8月19日）为残月，可见部分仅16%。文章还提供了观测建议，如使用肉眼或借助望远镜观察月球表面的特定地貌。同时，文章预告了下一个满月日期为9月7日，并详细解释了新月、娥眉月、上弦月、盈凸月、满月、亏凸月、下弦月、残月这八种月相的形成过程。

🌕 月相变化源于月球的29.5天公转周期，太阳、月球、地球之间角度的变化决定了月球被照亮部分的可见度。我们看到的月相是月球绕地球运行时，不同时刻被太阳照亮部分的形态。

🌟 当前（8月19日）月相为残月，月球表面只有16%被照亮，处于月相周期的第26天，月亮看起来较暗，是新月前的最后阶段。文章建议尝试用肉眼或借助望远镜观察月球表面的“阿里斯塔克斯高原”等细节。

📅 文章预告了下一个满月日期为9月7日，并回顾了上一个满月日期是8月9日。这为关注月相变化的用户提供了具体的时间参考。

💡 月相周期包含八个主要阶段：新月（不可见）、娥眉月（右侧出现细小月牙）、上弦月（右半边月亮可见）、盈凸月（大部分被照亮）、满月（整个月亮被照亮）、亏凸月（左侧开始变暗）、下弦月（左半边月亮可见）、残月（左侧出现细小月牙）。这些阶段循环往复，构成了月亮的可见性变化。

The moon is getting less and less visible each night, and it won't be long before we see nothing at all.

The moon is looking a little darker right now due to where we are in the lunar cycle, 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 let's see what's happening with the moon tonight, Aug. 19.

What is today’s moon phase?

As of Tuesday, Aug. 19, the moon phase is Waning Crescent, and it is 16% lit up to us on Earth, according to NASA's Daily Moon Observation.

We're on day 26 of the lunar cycle, and there's really not a whole lot for us to see tonight. With no visual aids other than your eyes, try and spot the Aristarchus Plateau. This is positioned in the top left of the moon (bottom right, if you're in the Southern Hemisphere).

With binoculars, see even more, including the Grimaldi Basin, and with a telescope, enjoy a glimpse of the Reiner Gamma.

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.