How Often Do Solar Eclipses Occur?
There are between 2 and 5 solar eclipses every year, each one visible only in a limited area.
Next Total Solar Eclipse: Mon, Dec 14, 2020 … See animation
Rare Solstice Annular Solar Eclipse
Missed our webcast? Watch a recording of our live hosted stream.
How Many Eclipses in a Year?
Most calendar years have 2 solar eclipses. The maximum number of solar eclipses that can take place in the same year is 5, but this is rare. According to NASA calculations, only about 25 years in the past 5,000 years have had 5 solar eclipses. The last time this happened was in 1935, and the next time will be in 2206.
Types of Solar Eclipses
There are 3 main types of solar eclipses:
In addition, there are hybrid solar eclipses, also called annular-total eclipses, when an annular eclipse changes into a total eclipse, or vice versa.
The darkest stage of a total, annular, or hybrid eclipse can only be seen from a small area. Still, solar eclipses, except hybrid eclipses, get their name from the maximum point of the eclipse, even if this point lasts less than a second. In reality, however, all solar eclipses look like partial solar eclipses in most places and for most of the duration.
When Does a Solar Eclipse Occur?
Solar eclipses can only happen around New Moon because of the alignment of Earth, the Moon, and the Sun which happens at that time. But this does not mean that eclipses of the Sun happen every New Moon night.
The New Moon and the Sun also have to be near a lunar node, which happens a little less than 6 months apart, and lasts, on average, around 34.5 days. This period is called the eclipse season, and it is the only time that eclipses take place.
The lunar nodes are the 2 points where the plane of the Moon's orbital path around Earth meets Earth's orbital plane around the Sun, the ecliptic. The orbital paths meet because the plane of the Moon's path around the Earth is inclined at an angle of approximately 5° to the ecliptic.
Solar Vs. Lunar Eclipses
Even though solar eclipses take place every year, they are considered a rare sight, much rarer than a lunar eclipse. This is because while a solar eclipse is only visible from a limited path on Earth, a lunar eclipse is visible from every location on the night side of the Earth while it lasts.
Total Eclipse in the US
On August 21, 2017, there was a total solar eclipse visible in a belt spanning all across the US. This was the first total solar eclipse visible from anywhere on mainland United States since the total solar eclipse in February 1979. The next total eclipse in the US is in April 2024.
On average, it takes about 375 years for a total solar eclipse to happen again at the same location. By comparison, a total lunar eclipse, also known as a Blood Moon, can be seen from any location approximately every 2.5 years.
How Often Do Solar and Lunar Eclipses Occur
Most years have 4 eclipses, which is the minimum number of eclipses that take place in a year; 2 of these 4 eclipses are always solar eclipses. While rare, the maximum number of eclipses that can take place in a calendar year is 7.
There are 2 or 3 eclipses during every eclipse season. At least 1 of these is always a solar eclipse, sometimes 2. The same is true for lunar eclipses. Which order they come in, depends on how each eclipse season coincides with the lunar (synodic) month.
The lunar month is the period it takes the Moon to go through all the Moon Phases from a New Moon to the next, and it lasts, on average, 29.5 days. This is 5 days less than an eclipse season, and therefore, there will always be at least 1 New Moon, resulting in a solar eclipse, and at least 1 Full Moon, resulting in a lunar eclipse, during each eclipse season.
This is also why solar and lunar eclipses come in pairs—a solar eclipse always takes place either about 2 weeks before or after a lunar eclipse, and vice versa.
At most, there can be 2 New Moons and 1 Full Moon, or 2 Full Moons and 1 New Moon in the same eclipse season.
Similar Eclipses Every 18 Years
Solar eclipses occur in cycles, called eclipse cycles. One of the most popularly studied eclipse cycles is the Saros cycle. The ancient Babylonians used it to predict lunar eclipses.
The Saros cycle is a period of approximately 6,585.3 days, or around 18 years, 11 days, and 8 hours, and it occurs due to a combination of 3 lunar cycles:
- The lunar (synodic) month: the time it takes from one New Moon to the next.
- The anomalistic month: the time it takes from Moon perigee to perigee, the point of the Moon's orbit closest to Earth.
- The draconic month: the time it takes from one lunar node to another. Also called the nodical month, it lasts, on average, 27.212220 days ( i.e., 27 days, 5 hours, 5 minutes, and 35.8 seconds).
2 solar eclipses separated by a Saros cycle have certain similarities—they occur at the same lunar node, with the Moon roughly at the same distance from Earth. The eclipses also take place around the same time of the year.