The Indian Express (Delhi Edition)
TOTALSOLARECLIPSEINNORTH AMERICA:WHYISTHISSORARE?
ON MONDAY, a total solar eclipse will cross North America, passing over Mexico, the United States, and Canada. It will not be visible in India, but this type of solar eclipse is a rare event for any particular spot.
What is a total solar eclipse?
A solar eclipse takes place when the Moon moves in between the Earth and the Sun. The Moon blocks the Sun’s light, either fully or partially, casting a huge shadow on some parts of the world.
There are four different types of solar eclipses — total solar eclipse, annual solar eclipse, partial solar eclipse, and hybrid solar eclipse.
When the Moon blocks the Sun entirely, the areas in the centre of the Moon’s shadow at the time witness a total solar eclipse.
When the Moon passes in front of the Sun but is at or near the farthest point from Earth, an annular solar eclipse occurs.
A partial solar eclipse happens when the Moon blocks just a part of the Sun, giving it a crescent shape.
A hybrid solar eclipse is witnessed when an eclipse shifts between annular and total solar eclipses as the shadow of the Moon moves across the globe.
How often is a solar eclipse seen?
A solar eclipse happens only during a new Moon — when the Moon and the Sun are aligned on the same side of Earth. Although a new Moon occurs in about 29.5 days, a solar eclipse takes place only between two and five times annually. This is because the Moon does not orbit the Earth in the same plane as the Earth orbits the Sun. The Moon’s orbit is tilted by about five degrees with respect to the Earth’s orbit around the Sun. As a result, usually when the Moon is in between the Sun and Earth, its shadow is either too high or too low to fall on the planet.
“If you think of the Earth’s orbit around the Sun as a disk and the Moon’s orbit around the Earth as another disk, there is a 5-degree angle between the two disks. However, any time you have two circles that intersect each other as the two disks do, there will be two points at which the intersection occurs... These two points on the Moon’s orbit (where the Moon lies in the same plane as the Earth’s orbit) are called nodes,” according to a report by Pennsylvania State University. Whenever the new Moon crosses one of these nodes, there is an opportunity for a solar eclipse.
Why is a total solar eclipse so rare?
A total solar eclipse at a given spot on Earth occurs only once in about 400 years. That is because a total solar eclipse is only visible if one is standing in the umbra — the middle and the darkest part of the lunar shadow. The umbral shadow is very small, and covers less than 1% of the globe during a solar eclipse.