Eclipses aren't rare events. Being in the right spot to witness one is. And if the weather doesn't cooperate, well ... you might have a very long wait until the next one comes along.

There are at least two and as many as five lunar eclipses every year; similarly there are, usually two and as many as five solar. A total eclipse of the sun happens once every 18 months, on average.

2020 promises to be a busy year, with four penumbral lunar eclipses, two of which will be visible in North America, including South Florida. Unfortunately an eclipse of the penumbral variety, as opposed to a total eclipse, are rather unspectacular events. Barely noticable, actually. A penumbral eclipse is when the earth's shadow, as opposed to the earth itself, passes between the sun and the moon. The shadow is known as a penumbra, thus the term.

There will be two solar eclipses, one total eclipse, but neither will be visible, even as a partial eclipse, anywhere in North America. The next one visible in the United States will be in 2024. The next total solar eclipse visible in South Florida won't be until the next century. At least. The last one: 1803.

The next total lunar eclipse will occur on May 26, 2021, but only a partial eclipse at best will be visible in North America. The next total lunar eclipse that we in South Florida will see will occur on the evening of May 15-16, 2022. That eclipse will be visible in most of the eastern United States.

Upcoming Lunar Eclipses

— January 10, 2020. Penumbral eclipse, visible in Europe, Africa, Asia and Australia.

— June 5, 2020. Penumbral eclipse, visible in parts of Europe, Africa, Asia and Australia.

— July 5, 2020. Penumbral eclipse, visible in the Americas, Europe and Africa.

— November 5, 2020. Penumbral eclipse, visible in North America, Asia and Europe.

Upcoming Solar Eclipses

— December 26, 2019. Annular* eclipse. Visible in eastern Europe, Africa, Asia and Australia. Path of totality sweeps through the Arabian Peninsula, southern India, Indonesia, southern Philippines and into the western Pacific.

— June 21, 2020. Annular* eclipse. Visible in Africa, southern and eastern Europe and Asia. Path of totality sweeps through west central Africa, the Arabian Peninsula, northern India, China and into the western Pacific.

— Dec. 14, 2020. Total eclipse. Visible in South America. Path of totality sweeps through the eastern Pacific, through Chile and Argentina, into the south Atlantic toward southern Africa.

A solar eclipse happens only when the moon is its new phase; a lunar eclipse only when the moon is full.

Two factors play into the regularity and the type of eclipse that we see. The orbit of the moon around the earth is elliptical rather than circular and is offset from the plain of the earth's orbit around the sun by about 5 degrees. Because the moon's orbit is elliptical, it has perigee — a point closest to the earth — and an apogee — a point farthest from the earth.

A total eclipse occurs when the moon is at its perigee, and the size of the moon as seen from earth is the same as the size of the sun. Only the corona — the outer most portion of the sun's atmosphere — is visible at totality. But only a small swath of the earth actually sees totality, a path about 100 miles wide extending perhaps as long as 10,000 miles. Larger areas on either side of the path see a partial eclipse. For example, during the 2017 eclipse, the path of totality swept through Columbia, S.C., while Jacksonville saw a sun that was 90 percent in shadow. In Miami, it was only 77 percent covered. A partial eclipse was visible as far south as South America.

An annular* solar eclipse, by contrast, occurs during a new moon when the moon itself is at its farthest point away from the earth, the apogee. This makes the moon appear smaller relative to the sun leaves firey ring around the disc of the moon at maximum cover. Annular, by the way, comes from the Greek word, annulus, meaning ring.

There are also partial eclipses, when the moon, sun and earth align imperfectly so that only a portion of the sun's surface is covered.

There is also a hybrid eclipse, which is seen as total in some places and annular in others. These are rare — only about five percent of all eclipses are hybrids.