Vernal Equinox Essay

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Phenomenon: The vernal equinox Explanation of an equinox The Earth’s rotation axis is tilted at an angle of 23.5 degrees from the perpendicular to the plane of the ecliptic. The ecliptic is the path of Earth’s orbit around the Sun. This gives rise to our four seasons due to the ever-shifting area of ground covered by sunlight. Every year, there are two equinoxes namely the vernal equinox and the autumnal equinox. An equinox is a day where the length of day and night are approximately equal throughout the world. The word equinox means ‘equal night’ in latin. To illustrate this, take for example a torch-light and a globe. Looking at the side view, if the light shines from the left to the right onto the globe, only about half of the globe, the side nearer to the light will be illuminated. There is a distinct line separating the bright side and the dark side, perpendicular to the direction of the light. This line is called the terminator. Other names include twilight zone and grey line. At exactly the time of northern winter solstice, the axial tilt of the Earth, the globe in this case is 23.5° to the terminator with the North Pole in the dark side and the South Pole in the bright side. An illustration of Northern Winter Solstice: Similarly, at the time of northern summer solstice, the tilt of the Earth (the globe) is also 23.5° to the terminator but with the South Pole in the dark side and the North Pole in the bright side. An illustration of Northern Summer Solstice: At the time of an equinox, the axial tilt is directly in the plane of the terminator, which means that the terminator meets both the North and South Poles; the sun is at the celestial equator. An illustration of the vernal equinox: With respect to the Northern Hemisphere, vernal equinox is the equinox in transition from the winter solstice to the summer solstice and happens between 20-22

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