21 June 2026 is the Summer Solstice with the Longest Daylight Duration of the Year

21 June 2026 "Summer Solstice" (Summer Solstice) is the day with the longest daylight duration in the year. Thailand will receive sunlight for the longest time, with the sun visible in the sky for about 12 hours and 56 minutes.

On 17 June 2026, the Facebook pageNARIT, the National Astronomical Research Institute of Thailand,posted that 21 June 2026 is the Summer Solstice, the day when the sun reaches its northernmost point, causing people around the world to see the sun rise at its most northeastern horizon and set at its most northwestern horizon. This results in countries in the Northern Hemisphere, including Thailand, experiencing their longest daylight and shortest nighttime periods, while countries in the Southern Hemisphere have their shortest daylight and longest nighttime periods. Thus, it marks the start of summer in the Northern Hemisphere and winter in the Southern Hemisphere.

For Thailand, on this day, the sun will rise at about 05:51 and set at about 18:47, with the sun visible for approximately 12 hours and 56 minutes (times for Bangkok). However, although this is the longest day of sunlight in the year for Thailand, due to its location near the equator and monsoon climate, seasons are mainly defined by weather patterns, and the Summer Solstice usually falls during the rainy season.

Seasons on Earth result from the Earth's axis tilting approximately 23.5 degrees relative to the perpendicular of its orbital plane around the sun, causing different areas to receive sunlight at varying angles and energy amounts. This affects temperature, lengths of day and night, and seasonal characteristics differently in each region. It also causes the sun's rising and setting positions to change daily, depending on the observer's latitude. Astronomically, four key phenomena relate to the sun's rising and setting positions:

• The Vernal Equinox, when the sun rises exactly in the east and sets exactly in the west, resulting in equal day and night lengths.
• The Summer Solstice, when the sun rises at its most northeastern point and sets at its most northwestern point, resulting in the longest day.
• The Autumnal Equinox, when the sun again rises exactly in the east and sets exactly in the west, resulting in equal day and night lengths.
• The Winter Solstice, when the sun rises at its most southeastern point and sets at its most southwestern point, resulting in the longest night.

These explanations refer to observations in the Northern Hemisphere, including Thailand. In the Southern Hemisphere, day and night lengths occur inversely. However, on the Vernal and Autumnal Equinoxes, most parts of the world experience roughly equal day and night lengths of about 12 hours.

The next related phenomenon concerning the sun's rising and setting is the "Autumnal Equinox," which falls on 23 September 2026. On this day, the sun will rise due east and set due west, resulting in equal lengths of day and night. This marks the start of autumn in the Northern Hemisphere and spring in the Southern Hemisphere. More information can be found on the Facebook page of NARIT, the National Astronomical Research Institute of Thailand.

Information credited to the Facebook page of NARIT, the National Astronomical Research Institute of Thailand.