What Is an Equinox

The term, ‘equinox’, refers to the days in the year when the length of the day and the night are equal. There are two days in the year when the phenomenon of equinox occurs. The sun is directly above the equator when equinox occurs and this accounts for the equal length of the day and night. There are two kinds of equinox namely, March equinox (spring equinox) and September equinox (autumn equinox). Though March 20th and September 22nd are considered to be the dates in the year when equinox occurs, there can be slight variation in the exact date when the phenomenon is seen in different parts of the earth depending on the distance of the region from the equator.

The origin of the term, ‘equinox’, is from the words, ‘aequus’, which means equal and ‘nox’, which refers to night. Different cultures associate different meanings to equinox and in some parts of the world, these days when equinox occurs are referred to as points in the year when a new season starts. The perfect explanation to the occurrence of equinox can be given as follows. Equinox occurs when the sun crosses the true celestial equator or the perpendicular that runs south to north into space from the equator.

It is to be noted that the length of the day is longer at the time of equinox at places that are at a greater distance from the equator. The explanation to the longer length of the day can also be attributed to the phenomenon of refraction that ensures that the sun is seen in the sky above the horizon a few minutes before it rises; and for few minutes after it sets. If one refers to the tables shared by authentic sources of space research, he can see that the there is a difference of almost 4 to 5 days between the occurrence of equinox in the 60 degree North and 60 degree South latitudes. Thus, arriving at an exact date with reference to equinox is impractical.

There are some interesting explanations associated with the occurrence of equinox. There are many cultures across the globe, which celebrate these days as special days when the departed souls of their loved ones take birth again. This can be explained as the reason as to why many countries have festivals and celebrations around this period of time. There are certain evidences from history too that early Mesopotamians and people from other civilizations had the knowledge about the occurrence of equinox twice a year. This goes on to showcase the fact that our ancestors too were advanced astronomically and attached great significance to the phenomenon of equinox. 

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