The Phenomenon of the Equinox

The equinox is one of the significant astronomical events that occur twice a year, where the length of day and night is approximately equal all over the world. However, the common understanding of this phenomenon might be somewhat simplified, as there are several factors that affect this apparent equality.

Understanding the Equinox

The equinox occurs when the sun crosses the celestial equator, resulting in equal lengths of day and night. This happens around March 20 and September 22 each year. Although the prevailing belief suggests a perfect balance between day and night, atmospheric and astronomical factors play a role in modifying this phenomenon.

One factor affecting the length of the day is atmospheric refraction, which causes the light to bend, making the sun appear above the horizon before its actual rise and after its true set. This refraction increases the length of the day compared to the night.

Challenges in Measuring the Equinox

When determining sunrise and sunset times, the moment the upper edge of the sun’s disk appears above the horizon is used, not the middle of the disk. This means that the day extends longer than the night even on the day of the equinox.

In some locations, such as Atlanta, it can be observed that the day lasts more than 12 hours during the equinox period. This requires scientists and astronomers to provide accurate explanations for this phenomenon.

Astronomical Effects on the Equinox

In the Arctic Circle, the sun can be seen making a complete circle around the horizon without fully setting. On the day of the autumnal equinox, the sun is supposed to disappear below the horizon, but due to refraction, it remains visible for a longer period. This phenomenon continues for up to 52 hours after the equinox.

Strong refraction also causes the sun’s disk to appear oval when it is near the horizon, as the lower edge is lifted more than the upper edge, distorting the shape of the disk.

Misconceptions About the Equinox

A common belief is that polar regions experience complete darkness for six months, which is not entirely accurate. Even in the Arctic, where the sun is absent for a long period, civil twilight persists for weeks before total darkness sets in.

Maritime and astronomical twilight extend for different periods, meaning that complete darkness only prevails in the Arctic for a short time compared to common belief.

Conclusion

It is important to understand the equinox deeply, as atmospheric and astronomical factors play a significant role in modifying natural phenomena. Although the equinox represents an apparent equality between day and night, the reality is more complex. Accurate knowledge of these phenomena helps correct common misconceptions and provides deeper insights into how the cosmic system operates.