当前正值农历月末，月球几乎完全不可见。根据NASA的数据，我们正处于29.5天月球周期的第27天。月球的可见度变化源于太阳照亮月球不同部分的角度变化，而月球则围绕地球运行。目前（9月19日）是亏凸月，可见度仅为5%。若无辅助设备，肉眼几乎无法观测，但借助望远镜可看到格里马尔迪环形山。下一个满月将在10月6日出现。文章还详细解释了新月、蛾眉月、上弦月、盈凸月、满月、亏凸月、下弦月和残月这八种主要的月相形成原因及特征。

🌕 **当前月相与观测提示**: 目前（9月19日）处于农历周期的第27天，月相为亏凸月，仅有5%的可见光照。肉眼几乎无法观测，但使用望远镜可看到格里马尔迪环形山，这为天文爱好者提供了特定的观测目标。

🚀 **月相变化的原因**: 月相的变化是由月球绕地球公转引起的，其29.5天的周期改变了太阳、月球和地球之间的角度。我们看到的月球亮度变化，实际上是太阳照亮月球不同部分在地球上呈现出的景象。

⭐ **八大主要月相**: 文章详细列举了八种主要的月相循环：新月（不可见）、盈凸月（右侧 sliver 亮）、上弦月（右侧半圆亮）、盈凸月（超过半圆亮）、满月（全圆亮）、亏凸月（右侧开始变暗）、下弦月（左侧半圆亮）和残月（左侧 sliver 亮），为理解月球周期提供了清晰框架。

We're approaching the end of this lunar cycle, and the moon is nearly completely out of view.

We're on day 27 of the lunar cycle, according to NASA, with it lasting 29.5 days in total. There are eight unique phases of the moon's visibility throughout, 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, Sept. 19.

What is today’s moon phase?

As of Friday, Sept. 19, the moon phase is Waning Crescent, and it is 5% lit up to us on Earth, according to NASA's Daily Moon Observation.

Visibility is low right now, and there's nothing to see without any visual aids. But if you have binoculars or a telescope, you'll be able to see the Grimaldi Basin.

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?

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.