An astronomical phenomenon known as a black moon will occur in the sky above Australia later this month.

Earth’s moon changes its appearance throughout the month as the Earth-facing side of the moon becomes more exposed or less exposed to the sun. This lunar cycle, which repeats every 29.5 days, begins and ends with a new moon and transitions to a full moon in the middle.

Image: Phases of the moon as seen from earth. Source: NASA/JPL-Caltech

Most calendar months contain one new moon and one full moon, and most astronomical seasons have three of each type of moon.

However, on rare occasions, a calendar month can have two full or new moons, and some astronomical seasons can have four new or full moons. These events are uncommon and have been given the unofficial names of a blue moon and a black moon.

The term black moon typically refers to one of two events:

• A second new moon that occurs in a single calendar month.
• The third new moon in an astronomical season that has four new moons.

A seasonal black moon will occur on August 23 this year, marking the third new moon in a season that will have four new moons. Note that the term ‘season’ here refers to the period between the solstice in June and equinox in September, not seasons based on calendar months.

Can you see the black moon?

Unfortunately, you can’t see this month’s black moon with a naked eye. This is because a new moon’s unlit face is oriented towards Earth and its sunlit face is pointing away from Earth.

Under good viewing conditions, you may see the unlit moon blocking a few stars, causing them to briefly disappear from the night sky.

Image: Track the moon phase using the 28-Day Calendar on the Weatherzone app.