Black moon arrives in Pacific Northwest skies Saturday. What is it?

PORTLAND, Ore. (KOIN) -- You've heard of "once in a blue moon," but what about a black moon?

According to OMSI, both lunar events are similar, with the blue moon being the second full moon of a single month. The black moon, on the other hand, is a second new moon appearing in the same month.

It is also set to appear in skies in western time zones - including Pacific - on Saturday, November 30, although it's highly unlikely you can see it.

"In the new moon, the moon is in between the earth and the sun," said Jim Todd, OMSI's Director of Space Science Education. "And the only way you can see the new moon, is during the solar eclipse like in 2017. That's why we don't see it. That's why it's defined as black."

Additionally, it turns out the black moon is actually not as rare as one would think. It all comes down to fortunate timing, according to Todd.

"So every month, we have a new moon, because it goes around the Earth 29 and a half days. That's called the lunar cycle. So every month we have a new moon. This month, because of the calendar system, we have two that falls on the calendar system," he said. "And so that means the lunar cycles goes around the Earth 13 times in one year, and every month we have a new moon. Timing is everything."

In the black moon's case, it only appears around every 29 months, with the last one in our area in July 2019.

For those who see the arrival of the black moon as an omen - given the bomb cyclone and the king tides on the Pacific coast as a result of the recent supermoon - Todd believes there's not much to worry about.

"Looking in the weather forecast look like we're going to be OK. We got some beautiful weather coming up around Thanksgiving," he said. "We might get some spectacular splashes at the Oregon coast, but that's it."

On Tuesday, November 26, the moon will also be in its apogee, the time when it's furthest away from earth. That means the tides will be weaker.

OMSI adds the rest of the world will experience the black moon on Dec. 1 and Dec. 30