As early astronomers studied the stars, using basic instruments they were able to figure out which day of the year was the longest, which day of the year was the shortest ,and which days had equal sunlight.
Welcome to MooMooMath and Science and what happens on the equinox and the solstice
Because the Earth is tilted at a 23.5 degrees angle and also rotates and revolves around the earth the length of the day varies though out the year
During each equinox, both hemispheres receive almost equal amounts of sunlight
12 hours of daylight and 12 hours of nighttime
The actual day in which both hemispheres receive exactly 12 hours sunlight and darkness is called the equilux and usually occurs a couple days before the march equinox and a few days after the September equinox.
The day of the solstice in either hemisphere has either the most sunlight of the year which is the summer solstice or the least sunlight of the year which is the (winter solstice) except at the equator.
Does the sun always rise exactly due east and due west ?
Remember the sun apears to rise and set due to the movement of the Earth
Actually the sun rises due east and sets due west two times a year. in each hemisphere
In the northern hemisphere on March 20 or 21 depending n the year you have the first day of spring and the sun is directly above the equator. This is called the vernal equinox. Vernal means fresh or new like spring. and the sun will rise due east. Moving forward the sun then starts rising a little more northeast each day until June 20th or 21st depending on the year . This is called the summer solstice and it is the longest day of the year. After the summer solstice sun starts rising less to the north until september 22nd or 23rd which is the autumn equinox. The sun will be directly above the equator again. After this the the sun will rise a little more southern until December 21st or 22nd which is the shortest day of the year called the winter solstice. After this day the sun will rise a little more northern until march 20th or 21st which is the vernal equinox. It takes a year to complete this cycle.
In the southern hemisphere the vernal equinox is september 22 or 23 the summer solstice is December 21 or 22, the autumnal equinox is March 20 or 21 and the winter solstice is June 20 or 21st.
Updated Video to fix some issues