本文介绍了月相的概念及其形成原因。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出的可见性周期。文章详细阐述了新月、峨眉月、上弦月、盈凸月、满月、亏凸月、下弦月、残月这八种主要的月相，并说明了它们在不同半球的观测方向。文章还预告了下一次满月的时间，并指出即使在月相变化时，我们看到的始终是月球的同一侧，只是被太阳照亮的部分不同。

🌕 月相是月球绕地球公转过程中，受太阳光照射角度变化而形成的可见性周期。根据NASA的解释，月球的不同相位是由于太阳照亮了月球在其绕地球轨道运行过程中不同部分的区域所致。这个周期被称为月球周期，包含八种独特的月相。

🔭 文章详细介绍了月球的八种主要月相及其特征。从完全不可见的“新月”开始，到逐渐增亮的“峨眉月”（北半球右侧出现一小片光），再到“上弦月”（右半侧被照亮，形似半月），接着是“盈凸月”（大部分被照亮但未满），直至“满月”（整个月面被完全照亮）。随后月亮开始“亏凸月”（右侧开始变暗），进入“下弦月”（左半侧被照亮，再次形似半月），最后是“残月”（左侧只剩细微光芒），直至再次回到新月。

✨ 观测者可以通过不同方式观察月球。仅凭肉眼，可在特定日期看到月海（如静海、风暴洋、丰富海）。使用双筒望远镜，可以看到更多的陨石坑（如波塞冬尼俄斯陨石坑、恩迪米翁陨石坑）和月海。借助望远镜，则能观测到更精细的地貌，甚至包括阿波罗登月点和笛卡尔高地。

📅 文章预告了下一次满月将在10月6日出现，而上一次满月则发生在9月7日。月相的变化遵循一个约29.5天的周期，这个周期是由太阳、月球和地球之间的角度变化决定的。尽管月相在不断变化，但我们始终看到的是月球的同一侧，只是其被太阳照亮的部分大小和位置在改变。

We're just a day away from a new lunar phase, which means we're close to seeing the moon half-lit up once again.

What is a lunar phase, you ask? Lunar phases make up the lunar cycle, a series of eight unique phases of the moon's visibility. According to NASA, these different phases happen as the Sun lights up different parts of the moon whilst it orbits Earth.

Keep reading to see what you can see when you look up tonight, Sept. 28.

What is today’s moon phase?

As of Sunday, Sept. 28, the moon phase is Waxing Crescent, and according to NASA's Daily Moon Observation, 36% of its surface is illuminated tonight.

There's plenty to see tonight, so adjust your gaze and look upwards. With just your naked eye, you'll see the Mare Crisium, Mare Tranquillitatis, and the Mare Fecunditatis. If you're in the Northern Hemisphere, these are all positioned towards the right of the moon, from the middle upwards. If you're in the Southern Hemisphere, look to the bottom left.

If you've got a pair of binoculars, pull them out to see the Posidonius Crater, the Endymion Crater, and the Mare Nectaris. With a telescope, you'll see all this and the Apollo 17 and 11 landing spots and the Descartes Highlands.

When is the next full moon?

The next full moon will be on Oct. 6. The last full moon was on Sept. 7.

What are moon phases?

NASA tells us that moon phases are part of a 29.5-day cycle of the moon’s orbit. This changes the angles between the Sun, Moon, and Earth. Moon phases are how the moon looks from Earth as it goes around us; sometimes it looks full, sometimes it looks like it's disappeared entirely, but we always see the same side of the moon, it's just how much of it is lit up by the Sun that 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.