Why Don't Solar Eclipses Happen More Often and When Do I Need to Wear Eclipse Glasses?
Solar eclipses do not occur every month because their occurrence is dependent on the alignment of the Sun, Moon, and Earth. Solar eclipses specifically occur during a new moon, when the Moon passes between the Earth and the Sun, casting a shadow on the Earth's surface. However, three conditions need to be met for a solar eclipse to take place:
1. Alignment of the Sun, Moon, and Earth: The Moon must be in the correct position between the Sun and Earth to cast its shadow on Earth's surface. During a new moon, the Moon is generally positioned slightly above or below the Sun in the sky, resulting in most new moons not producing a solar eclipse.
2. Orbital inclination of the Moon: The Moon's orbit is inclined by about 5 degrees relative to Earth's orbit around the Sun. This means that the Moon's shadow usually passes above or below the Earth's surface during a new moon, resulting in a miss rather than an eclipse.
3. Synchronization of the lunar and solar cycles: The lunar cycle, which determines the phases of the Moon, is about 29.5 days long, while the solar cycle, which is the time it takes for the Sun to return to the same position in the sky, is about 365.25 days long. This discrepancy means that the alignment required for a solar eclipse does not happen with every new moon.
To have a solar eclipse, the Moon must be in the correct position, not too high or low in its orbit, and the timing should be such that the new moon occurs when the Moon is crossing the plane of Earth's orbit around the Sun. These conditions are met only a few times a year, resulting in solar eclipses being relatively rare events.
It's worth noting that even when a solar eclipse occurs, it is visible only from a specific region on Earth where the Moon's shadow falls. The path of totality, where the Sun is completely blocked by the Moon, is usually narrow, and the partial eclipse can be seen from a broader area surrounding it.
In short: if it is an annular eclipse (October 2023), you need eclipse glasses for the entirety of the eclipse. If it is a total eclipse (April 2024), you need eclipse glasses before and after totality.