[Physics Class Notes] on Equinox Astronomy Pdf for Exam

An equinox meaning is an event in which a planet’s subsolar point passes through its Equator, and the day and night remain of equal length. Equinoxes appear when both the Northern and Southern Hemisphere experience roughly equal amounts of daytime and nighttime. Regarding the equinox solar system, either of the two points presents in the sky where the Sun’s annual pathway- ecliptic and the celestial equator interest. Multiple ancient monuments mark the equinoxes, like the Hindu temple complex Angkor Wat in Cambodia, situated at the spot where the Sun rises directly above its central temple. 

Two equinoxes occur-  Autumnal and the Vernal Equinox. The autumnal equinox falls on September 23, when the Sun crosses past the celestial equator going south. The Vernal equinox occurs on March 21, which marks the beginning of spring in the Northern Hemisphere. This is a typical equinox example. 

Equinox Space Definition

Equinox space definition occurs where the day and night are almost of the same length and occurs twice a year in both the Northern and Southern Hemispheres. This phenomenon is known as Equinox, meaning equal parts, derived from the Latin words’ aequus’, which means equal, and ‘nox’, which means night. Equinoxes are historic insignia of seasonal change.

What Causes an Equinox?

The Earth orbits the Sun at a tilt of about 23.5 degrees, leading to different parts of our planet receiving more or less of the Sun’s radiation at various times of the year, depending on the planet’s position in its orbit. All countries witness the Sunrise in the East and set in the West. However, the Sun also moves to the North for half the year and South the remaining half time of the year. This depends on where the country is located. 

The Northern Hemisphere experiences a more extended period of daylight, while the Southern Hemisphere experiences shorter sunlight periods around July. Around the time of December, the vice-versa occurs. However, twice a year- March and September, the Earth’s tilt aligns with the orbit around the Sun.

At this time of the year, the Sun is directly overhead above the equator, and both the Northern and Southern Hemispheres get the same hours of daylight and night. The line that divides the day and night during an Equinox is known as the ‘grey line’ or ‘twilight zone’, and this line bisects the Earth through the South and North poles. 

During an Equinox in the solar system, the Earth gets a few more minutes of light over darkness. Sunrise occurs when the Sun’s tip edges over the horizon, and sunset is when the Sun’s end disappears over the other edge under the skyline. 

Equilux is also known as ‘equal light’; it’s used when the day and night are exactly equal because of how Sunrise and sunset are defined. The phase of equilux occurs a few days before the spring equinox and a few days after the autumn equinox.

When Do Equinoxes Occur?

Equinoxes do not necessarily occur on the same day each year. Instead, the Equinox occurrences happen during the spring of March 20 and the fall of September 23. These shifting dates are because the Earth’s year is not exactly 365 days as there happens to be an extra quarter of a day with approximately 6 hours that accumulates each year. This disruption causes the date of the Equinox to shift to two different time frames of the year. The Earth’s orientation towards the Sun also constantly moves, tweaking the timing of the Equinox.

The Equinoxes mark the beginning of two seasons- Spring and Autumn, depending on the Hemispheres- Northern or Southern. However, the meteorological start of these two seasons is March 1 and September 1, respectively.

In the Northern hemisphere, the March equinox heralds the beginning of the Spring season, and the phase is known as Vernal or Spring Equinox. The term ‘vernal’ comes from the Latin word ‘ver’, meaning spring. Simultaneously, the Southern hemisphere shifts to experience Autumn. The converse is true in September when the Northern half descends into Autumn’s cold wintertime, the Southern half experiences Spring.

Earth is not the only celestial body that experiences equinoxes. In fact. Every other planet in the solar system holds equinoxes when the planet’s orbit and tilt align with the Sun resulting in both the hemispheres receiving roughly equal amounts of light and darkness.