Bangkok: The National Astronomical Research Institute of Thailand (NARIT) has provided insights into the vernal equinox, a significant astronomical event when daytime and nighttime are of equal length. On March 20, 1969, the sun was directly perpendicular to the Earth's equator, causing this balance of day and night worldwide. This event signifies the onset of spring in the Northern Hemisphere and autumn in the Southern Hemisphere.

According to Thai News Agency, the term "vernal equinox" is derived from Sanskrit, meaning "point of equal night and day." On this day, the sun rises precisely on the eastern horizon and sets exactly on the western horizon. In Thailand, the sun rose at approximately 6:22 AM and set at approximately 6:28 PM, marking the seasonal transition.

The explanation for sunrise and sunset times during such phenomena is based on the moment the sun's "upper edge" touches the horizon. This occurrence may make sunrise and sunset times appear to vary, but it does not affect the equal length of day and night. When measured from the midpoint of the sun crossing the horizon, the day consists of exactly 12 hours of daylight and 12 hours of nighttime.

The occurrence of seasons on Earth is attributed to the planet's axial tilt of 23.5 degrees relative to its orbital plane around the sun. This tilt results in variations in sunlight intensity and heat energy distribution, leading to seasonal changes. During summer, days are longer due to early sunrises and late sunsets, while winter experiences longer nights with late sunrises and early sunsets.

The next notable astronomical event related to sunrise and sunset will be the "Summer Solstice" on June 21, 2026. On this day, the sun rises furthest to the northeast and sets furthest to the northwest, resulting in the longest day of the year. This marks the beginning of summer in the Northern Hemisphere and winter in the Southern Hemisphere.